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After the cancellation of last year's annual meeting due to the Corona pandemic, we are optimistic that we can organize our annual meeting in the usual way. Continuing the well-established tradition, every two years ÖPG and SPS hold their annual meetings together, alternating the conference location between Austria and Switzerland.
This year the conference is planned in the week of 30 August - 3 September on the "Campus Technik" of the University of Innsbruck.
As usual, renowned invited speakers will give plenary talks during each of the morning sessions, topical parallel sessions will allow in depth discussions during the afternoons, and a poster exhibition will complement the scientific program.
The scientific program is further enriched by the direct contributions of the Swiss Institute for Particle Physics (CHIPP) and the SFB BeyondC. Thanks to all these collaborations, the joint annual meeting will offer again an exciting program, covering latest advancements of physics in a wide range of fields at its best.
Updates:
Registration Deadline: 17 August 2021
Note: With submitting an abstract you are NOT automatically registered. Use the registration form to do so.
The arrangement of the top layer of atoms on a solid – and the resulting electronic and chemical properties – affect and sometimes even dominate its functionality. In the talk, I will showcase how we can use basic physical phenomena – tunneling, diffraction, and change in resonance frequencies – to measure surface properties in an atom-by-atom fashion. By investigating well-defined samples in a controlled environment, such experiments can be tightly interlinked with theoretical computations. Examples include assessing the acidity of individual surface atoms; pushing the size of catalytically-active nanoclusters to their physical limit; and extending ultrahigh-vacuum experiments to the liquid phase.
I will discuss how the first image of a black hole was obtained by the Event Horizon Telescope-EHT collaboration. In particular, I will describe the theoretical aspects that have allowed us to model the dynamics of the plasma accreting onto the black hole and how such dynamics was used to generate synthetic black-hole images. I will also illustrate how the comparison between the theoretical images and the observations has allowed us to deduce the presence of a black hole in M87 and to extract information about its properties. Finally, I will outline the lessons we have learned about strong-field gravity and alternatives to black holes.
We investigate a homogeneous system of dipolar bosons in 2D including a short-range repulsion. Varying the strength of this repulsion and the angle of the dipoles with respect to the 2D plane, we find strong evidence for the formation
of a striped and self-bound state in the form of a diverging peak at finite wave vector in the structure factor. We employ the variational
hypernetted-chain Euler-Lagrange method, which we previously applied to self-bound Bose mixtures. It accounts
for correlations nonperturbatively, and is very efficient compared to exact quantum Monte-Carlo simulations.
We accurately calculate properties of the ground-state of the dipoles and validate our results by comparison with diffusion Monte-Carlo calculations.
We present our studies on polarons in a strongly interacting mixture formed by bosonic 41K impurities immersed in a Fermi sea of ultracold 6Li atoms, investigated by means of radio-frequency spectroscopy. The impurities can be either a thermal cloud or a partial Bose-Einstein condensate. The polaron energy for both the thermal cloud and the thermal part of the partial condensate can be described by a single impurity Fermi polaron, while the condensate fraction gives birth to a new branch in the radio-frequency spectrum, which can be explained by a Bose polaron.
We report on the realization of a novel, strongly interacting degenerate Fermi-Fermi mixture, which is a promising system for creating a mass-imbalanced fermionic superfluid. The mixture is brought into the deeply degenerate regime at low magnetic field: A narrow-line laser cooling stage allows for an optimization of the starting conditions for the subsequent evaporative cooling. We found a strong interspecies Feshbach resonance at a magnetic field near 217G. The transfer to high magnetic field requires careful steps, so to minimize losses and heating due to the presence of many narrow Feshbach resonances. On resonance, we reach a temperature of about 50nK: By tuning the population imbalance, superfluidity is in reach.
We report on the observation of confinement-induced resonances (CIRs) for strong zero-dimensional (0D) confinement in a three-dimensional (3D) optical lattice potential. Starting from a Mott-insulator state with mainly single-site occupancy, we detect loss and heating features at specific values for the confinement length scale and the 3D scattering length. Two independent models, describing the coupling between the center-of-mass and the relative motion of the particles as mediated by the lattice, predict the resonance positions to a good approximation, suggesting a universal behavior. Our results show that CIRs exist for any dimensionality and open up a new method for interaction tuning and controlled molecule formation under strong 0D confinement.
In our current experiments we are focusing on the dynamics of an impurity subjected to a uniform velocity in a highly confined and correlated system. If the initial velocity of the impurity is above the super sonic value the final velocity is not constant but rather displays a small oscillation. These unexpected dynamics have been coined quantum flutter in previous publications [2,3]. Here we will discuss the measurements that we have recently obtained in this area.
[2] C. Mathy et. al, Nat. Phys., 8 (2012)
[3] M. Knap et. al, Phys. Rev. Lett., 112, 015302 (2014)
Topological pumps allow robust quantized transport of particles in periodic potentials. Their topological origin is analogous to the quantum Hall effect. In atomic physics, ultracold atoms in optical lattices are versatile systems to observe such effects. Yet, charge pumping has been limited to super-lattices operating with a sliding potential. Here, we experimentally realize a topological pump of ultracold fermions in a simple one dimensional optical lattice. The optical lattice is resonantly shaken to prepare the fermions in a topological Floquet-Bloch band. Pumping is achieved by periodically modulating the shaking waveform slow enough to ensure adiabaticity. Our results pave the way for observing topological pumps in Floquet-Bloch bands in real materials.
The time evolution of a quantum system can be strongly affected by dissipation. In our experiment, we study a Bose-Einstein Condensate coupled to a high finesse resonator. The cavity mode is populated via the atoms, such that the sum of the coupling beam(s) and the intracavity standing wave gives an optical lattice potential. When the dissipative and the coherent timescales are comparable, we find a regime of persistent oscillations where the cavity field does not reach a steady state. Eventually, the dynamical lattice triggers a pumping mechanism. We will show complementary measurements of the light field and of the atomic transport, proving the connection between the non-stationarity and the pump.
We consider a V-shaped three-level system coupled to orthogonal quadratures of a dissipative cavity field, and observe a significant multistability of states with inverted atomic population. The stability of these inverted states are closely related to properties of dark states, and is a combined result of the cavity dissipation and the underlying SU(3) symmetry of the atomic subsystem. The multistability can be probed due to three factors: the stability of the normal state is significantly suppressed; the system trajectories and final states of dynamical evolutions are highly sensitive to ramping scheme; and different inverted states have their own characteristic cavity fluctuations.
We present the concept of the spatial affinity lock-in amplifier to reject environmental noise in label-free biosensing at the example of focal molography. Molography is a sensitive and robust implementation of a diffractometric biosensor and has emerged as a new platform technology to study biomolecular interactions label-free in complex fluids and living cells. Molography is insensitive to environmental noise (temperature gradients and nonspecific binding). It achieves this by modulating the analyte binding at a high spatial frequency and reads it out in Fourier space via diffraction of light at the bound molecules. We will end with an outlook on applications that may be enabled by the spatial lock-in principle.
In-vitro cell cluster models, as cancer spheroids and organoids, have become valuable models in the life sciences. We have developed a sono-optical microfluidic device with 3D acoustic trapping and optical tweezers for non-contact manipulation and imaging of such samples in liquid suspension. With 3D independent control of the transducers we can adjust the relative strength of the acoustic radiation and viscous torques which will determine whether transient reorientation or continuous rotation of a given sample takes place. With acoustics alone or combined with optical tweezers, we can trap samples, change their location and orientation or induce sustained rotation of them which offers access to 3D optical inspection and tomographic information.
The mechanical forces involved during tissue morphogenesis have been the focus of much research in recent years. Absolute values of forces during tissue closure events have not yet been measured. This is also true for a common force producing mechanism involving MyosinII waves resulting in pulsed cell contractions. A magnetic tweezer, combined with confocal microscopy provides a powerful tool to quantitatively measure forces during tissue morphogenesis. Here, we quantify the in vivo force production of MyosinII waves observed at the dorsal surface of the yolk cell in Drosophila embryos. In addition to providing quantitative values on the force, we elucidated the dynamics of the MyosinII waves by measuring their periodicity.
The PETITION (PET for InTensive care units and Innovative protON therapy) collaboration recently started to develop two Positron Emission Tomography (PET) systems to enable novel clinical applications. The first system (ICU-system) will be a mobile brain PET scanner, for the intensive care unit. The second system (PBT-system) will be employed in proton beam therapy featuring an opening for proton irradiation during image acquisition. A series of Monte-Carlo simulations have been done to obtain performance estimates. We measure a peak sensitivity of 2.66% (1.74%) for the ICU-system (PBT-system). For the spatial resolution we obtain values between 2.2mm and 2.7mm for the central region with both systems, matching well with the expectations.
Ion therapy treatment planning requires an accurate estimate of the energy deposition of the ions per path length (stopping power) in the patient. From a conventional planning CT, Hounsfield units are obtained that have to be converted to stopping power values leading to range uncertainties. Ion computed tomography (iCT) allows to directly measure this quantity. In this scope, research activities of our group, with emphasis on GPU-based image reconstruction, the implementation of an ion CT demonstrator at MedAustron as well as upgrade possibilities, will be presented.
Despite theoretical predictions for the Cherenkov radiation of spin waves (magnons) by various propagating magnetic perturbations, it has not been observed so far. Our recent experiments arXiv:2103.10156 evidence the Cherenkov radiation of magnons in a Co-Fe magnonic conduit by fast-moving magnetic flux quanta (Abrikosov vortices) in an adjacent Nb-C superconducting strip. The radiation is evidenced by the microwave detection of spin waves and it is accompanied by a magnon Shapiro step in superconductor's current-voltage curve. The spin-wave excitation is unidirectional and monochromatic, with sub-40 nm wavelengths determined by the period of the vortex lattice. The magnon/fluxon phase-locking limits the vortex velocity and reduces the dissipation in the superconductor.
Magnons, the quanta of spin waves, could be used to encode information in beyond-Moore computing applications. Here, we report a nano-scale magnonic directional coupler based on yttrium iron garnet , which can function as circuit building blocks. The coupler consists of single-mode waveguides with a width of 350 nm. We use the amplitude of a spin wave to encode information and to guide it to one of the two outputs of the coupler depending on the signal magnitude, frequency and the applied magnetic field. Using micromagnetic simulations, we also propose an integrated magnonic half-adder that consists of two directional couplers and we investigate its functionality for information processing.
Spin waves, and their quanta magnons, are of great interest as potential data carriers in future low-energy computing devices. Here, we will present the method of inverse-design magnonics, in which any functionality can be specified first, and a feedback-based computational algorithm is used to obtain the device design. Our proof-of-concept prototype is based on a rectangular ferromagnetic area that can be patterned using square-shaped voids. We explore linear, nonlinear, and nonreciprocal magnonic functionalities and use the same algorithm to create a magnonic (de-)multiplexer, a nonlinear switch, and a circulator. Thus, inverse-design magnonics can be used to develop highly efficient rf applications as well as Boolean and neuromorphic computing building blocks.
Long-lived coherences, emerging under periodic pulse driving in the disordered ensembles of strongly interacting spins, offer immense advantages for future quantum technologies, but the physical origin and the key properties of this phenomenon remain poorly understood. We theoretically investigate this effect in ensembles of different dimensionality, and predict existence of the long-lived coherences in all such systems, from two-dimensional to infinite-dimensional, which are of particular importance for quantum sensing and quantum information processing. We explore the transition from two to infinite dimensions, and show that the long-time coherence dynamics in all dimensionalities is qualitatively similar, although the short-time behavior is drastically different, exhibiting dimensionality-dependent singularity.
In this contribution we present direct imaging of spin-wave dynamics in Ni$_{80}$Fe$_{20}$ rectangular microstrips ($5\times1\times0.03$ µm$^3$) under uniform excitation. Both a single strip and two strips of the same size oriented perpendicular to each other are investigated. For FMR and time-resolved STXM measurements a static magnetic field is applied in plane, aligned parallel or perpendicular to the longer side of the strips. The measurements confirm that quasi-uniform and spin-wave excitations can be observed in these geometries. Increasing the static magnetic field allows to observe the spin-waves at resonance fields and their superposition off resonance. A non-standing character of spin waves under uniform excitation is reported. Financial support by FWF (P.Nr.:I-3050).
We present a microscopic study of a doped quantum spin liquid candidate, the Hyperkagome Na3Ir3O8 compound, by using 23Na NMR (1). We determine the intrinsic behavior of the uniform q = 0 susceptibility via shift measurements and the dynamical response by probing the spin-lattice relaxation rate. Throughout the studied temperature range, the susceptibility is consistent with a semimetal behavior, though with electronic bands substantially modified by correlations. Remarkably, the antiferromagnetic fluctuations present in the insulating parent compound Na4Ir3O8 survive in the studied compound. The spin dynamics are consistent with 120 degrees excitation modes displaying short-range correlations.
Metastable skyrmions with long lifetimes are attractive for various applications. However, the physics behind the non-equilibrium topological phases is far from being fully understood. We report the creation of a new hidden skyrmion phase in a Cu2OSeO3 lamella achieved by femtosecond laser excitation of the material at 5 K and a magnetic field of 15 mT. The formation of the skyrmion lattice was confirmed by Lorentz-TEM. Since this small magnetic field is below the equilibrium skyrmion pocket of our lamella, the generation of skyrmions cannot be explained by transient heating of the sample through the equilibrium skyrmion pocket. Thus, non-thermal mechanisms are involved in the skyrmion photocreation process in Cu2OSeO3.
The insulating multiferroic material Cu2OSeO3 holds the possibility to study and manipulate topological magnetic order and skyrmion dynamics in a current free environment, purely under the influence of magnons or electric field. Here we drive and control ratchet-like skyrmion rotational motion via femtosecond pulses of mid-infrared (1 eV) light, far below the bandgap of the material. We image the skyrmion lattice in real space via Lorentz transmission electron microscopy after each laser pulse. This direct manipulation via a combination of low-energy magnons and electric field (contained within the femtosecond laser pulse) could be used to build spin memory and logical devices with much lower dissipation losses than previously achieved.
In a superconductor with inversion, spin-singlet and spin-triplet order parameters are distinct by symmetry and can be distinguished experimentally through their magnetic response. In non-centrosymmetric systems, however, the two order parameters mix and the magnetic response is inconclusive. In our work, we examine the situation, where inversion is broken locally in a sublattice, but retained globally. In particular, we investigate a system consisting of layers with alternating Rashba spin-orbit coupling in the z direction. In this case, the system shows signs of non-centrosymmetricity even in the three-dimensional limit. This opens a design path to new superconducting order parameters which are robust against magnetism.
With the availability of internet, social media, etc., the interconnectedness of people within most societies has increased tremendously over the past decades. Across the same timespan, an increasing level of fragmentation of society into small groups has been observed. With a simple model of societies, in which the dynamics of opinion formation is integrated with social balance, we show that these two phenomena might be tightly related. We identify a critical level of interconnectedness, above which society fragments into subcommunities that are internally cohesive and hostile towards other groups. This critical density necessarily arises from the underlying mathematical structure of a phase transition known from the theory of spin glasses.
Arthur E. Haas (1884-1941) was an Austrian theoretical physicist, one of the last students of Ludwig Boltzmann, and today mainly known for his early contributions to quantum physics. In the 1920s he was a very successful author of several textbooks and popular science books on topics of modern physics. He gave multiple lectures in Vienna and Berlin, and across the entire United States. He was a "Carl Sagan" of his time. In the early 1930s he shifted his focus from quantum physics to cosmology. Haas emigrated in 1935 from Austria to the United States and assumed, on recommendation of Albert Einstein, a faculty position at the University of Notre Dame.
Optical spectroscopy was an important field of research at the University Vienna around the year 1900. Several devices are still kept in the historical collection of the Faculty of Physics and some are presented in this talk. Franz Serafin Exner (1849-1926) wanted to use optical spectroscopy to find new chemical elements in meteorites, which were available at the Natural History Museum Vienna. However, he did not realize his original idea, as he and his co-worker, Eduard Haschek (1875 – 1947), dedicated a lot of time in creating spectroscopic data for all chemical elements being available at their time. Highlight was the use of an original 15 feet Rowland concave grating.
Boltzmann’s H-theorem has revolutionized the thinking about the evolution of entropy in thermodynamics. It has proved the unidirectional tendency of irreversible processes contradicting the time-reversed laws of physics (Loschmidt’s and Poincaré’s paradox). However, the entropy is quantified as a state variable and defines quasistatic equilibrium in an infinite time limit. The H-theorem flashed over to information theory and was first investigated in a thought experiment by L. Szilard, later culminating in Landauer’s erasure principle. Shannon's measure of information has been allegedly suggested by J. von Neumann as “entropy”, or “negentropy” (E. Schrödinger, L. Brillouin). The (mis)interpretation of disorder and informational entropy and their relationship is outlined by means of examples.
Ideas of Wilhelm Lenz 1921 and Walter Schottky 1922 how Coulomb energy might induce an interaction which orders the elementary magnetons made possible the formulation of a corresponding model by Ernst Ising 1925 but did not lead to a magnetic phase. Only the development of the new quantum mechanics allowed Pauli to formulated 1930 at the Solvay conference the Ising model as we know it nowadays. These parallel developments were made by physicists whose academic career crossed in the 1920's at the University of Hamburg the first democratic foundation of a German university
Supported by the Austrian Agency for International Cooperation in Education and Research Project No. UA 09/2020
Flavour physics studies the different generations of fermions in the Standard Model (SM). The origin of flavour is, as of today, completely unknown. Flavour physics can inform efforts to produce a new theory beyond the SM, explaining phenomena such as dark matter and antimatter disappearance.
Recently, the LHCb experiment uncovered anomalies in lepton flavours. Hints of violation of “lepton flavour universality” (LFU) i.e. the identity of the three lepton families in electroweak interactions were detected in several B meson decays.
This presentation will review these findings in neutral-current B decays, give an outlook for the near future and briefly discuss how these measurements can be used to formulate new theories
The Lepton Flavour Universality (LFU) anomalies are currently one of the hottest topics in the particle physics community. A combination of recent results from LHCb, Belle and BaBar from charged-current decays of B mesons have shown a discrepancy from the Standard Model prediction of ~3 σ. This talk will review the latest lepton universality tests with b → clν decays and present the progresses for an independent LFU test with baryons using baryonic Λb→Λc decays. This test is important both to corroborate the present anomalies and to provide complementary constraints on the possible origins of these anomalies beyond the Standard Model.
While the LHC has not discovered any new particles directly yet, hints for the violation of lepton flavour universality (satisfied within the SM) accumulated in recent years. In particular, deviations from the SM predictions were observed in semi-leptonic B decays (b->sll and b->ctau), in the anomalous magnetic moment of the muon (g-2), in leptonic tau decays and di-electron searches. Furthermore, also the deficit in first row CKM unitarity, known as the Cabibbo Angle Anomaly, can be interpreted as a sign of lepton flavour universality violation. In this talk I review the status of these anomalies and give an overview of the possible interpretations in terms of new physics models.
Ratios of branching fractions such as $R_{K}= \mathcal{B}(B^{+}\rightarrow K^{+}\mu^{+}\mu^{-})/\mathcal{B}(B^{+}\rightarrow K^{+}e^{+}e^{-})$ are clean probes of lepton flavour universality (LFU) violation. LHCb published the most accurate measurement of this observable up to date, yielding a value $3.1\sigma$ away from the Standard Model prediction, providing the first evidence of LFU violation. This is another piece added to the puzzle of flavour anomalies observed in different processes governed by the $b \rightarrow s \ell \ell$ transition. I will give an overview of the measurement of $R_{K}$ and illustrate a method to assess the global significance of the New Physics hypothesis in the $b \rightarrow s \ell \ell$ system taking into account the Look-elsewhere effect.
Recent studies of rare semileptonic decays of beauty mesons reported some intriguing discrepancies with the SM predictions, which seem to form a coherent pattern. Of particular interest are the angular observable P5' of the B→Kμ+μ- decay and the suppression of the muon channel in the ratios of branching fractions of B+→K+μ+μ− to B+→K+e+e− transitions.
The proposed research aims to perform an unbinned likelihood amplitude fit of B→ Kl+l- decays with the full LHCb run-I/II dataset, simultaneously to the muon and electron channel. This approach intends to disentangle the hadronic-dependent part from a q2-independent New Physics(NP) contribution in a theoretically accurate and experimentally sensitive manner, establishing eventually an evidence of NP.
The family of decays mediated by $b \to s \ell^+ \ell^-$ transitions ($\ell = \mu, e$) provides a rich laboratory to search for physics beyond the Standard Model. In recent years, LHCb has found hints of deviations from theoretical predictions notably in lepton flavour universality (LFU) testing branching fraction ratios (\textit{i.e.} $R_{K}$ and $R_{K^{*0}}$), as well as angular distributions of the $B^0 \to K^{*0} \mu^+\mu^-$ decay. The angular analysis of the electron mode allows for the investigation of LFU in angular distributions, especially in the observable $P^{\prime}_{5}$. In this work I will show the current status and prospects for the angular analysis of $B^0 \to K^{*0} e^+e^-$ decays at LHCb.
The recently updated value of the ratio of branching fractions $R_K = \mathcal{B}(B^+ \to K^+\mu^+\mu^-)~/~\mathcal{B}(B^+ \to K^+e^+e^-)$ that has been calculated for a dilepton invariant mass squared range $q\mathrm{^2 \in (1.1~GeV^2,~6.0~GeV^2)}$ is in tension with the Standard Model prediction at the level of 3.1 $\sigma$. I will discuss a complementary study in the high $q\mathrm{^2 > 14~GeV^2}$ region using the same $\mathrm{9~fm^{-1}}$ of proton-proton collision data recorded by the LHCb experiment at CERN's Large Hadron Collider. The result is expected to be statistically and systematically independent of the existing central $q\mathrm{^2}$ measurement and will be a vital measurement in clarifying the presence of new physics in this system.
New exciting results have been published by the LHCb experiment on the Lepton Flavour Universality (LFU), especially in rare loop-mediated processes. To further corroborate or discard New Physics (NP) scenarios, additional testing is needed at fundamental tree-level processes: baryonic semi-leptonic decays provide a unique means to test for LFU at the LHCb, given e.g. their production abundance and favourable BR. In addition, they exhibit enhanced sensitivity to NP in the angular observables of the decay products. I present the angular analysis of the process $\Lambda_b \to \Lambda_c \mu \nu$ as a function of the squared di-lepton invariant mass and lepton helicity angle.
Lepton flavour universality tests, that could reveal hints for new beyond the Standard Model phenomena, can be pursued with data collected by the CMS experiment at a center of mass energy of 13 TeV. During the talk, a specific measurement will be presented, with focus on the approaches and methodology pursued, showing the performances involved towards the finalisation of the measurement.
Non standard model contributions to CP-violation are required to explain the matter-antimatter asymmetry in the universe. To challenge this ATLAS is measuring CP-violation to high precision in decays of the Bs meson. A dominant source of systematics is detector alignment, which has to be under control. Moreover, a test of the universality of tau and muon lepton couplings in W-boson decays from tt-bar events will be presented.
Recently 2D networks of sp2 hybridized B-atoms, called Borophene, have been grown on (111) faces of Cu, Ag and Au and on Ag(110). Borophene, presumably exhibiting highly interesting physical, chemical and electrical properties, does not exist as a bulk layered material, hence it cannot be studied via exfoliation. We investigated the growth of different Borophene phases via bulk segregation of B on Pt(110) by means of scanning tunneling microscopy. Despite the strong anisotropy of the Pt(110) template, different orientations of the triangular Borophene lattice are observed. The vacancy concentration varies, suggesting that it is not only controlled by charge transfer.
The observation of h-BN single-domain growth on Pt(110) calls for an investigation of the mechanism eliminating rotational domains. We investigated the transformation of a chemisorbed layer of Borazine into h-BN islands upon heating via UV photoemission and STM. Evidence is presented for a non-classical, two-step nucleation process with a metastable 1D precursor phase. Non-classical nucleation is mainly observed in crystallization of biomolecules and still under dispute as far as inorganic materials are concerned. The present example is the first one reported for 2D crystallization processes. However, the protocol used here yields various domains indicating a fundamental difference to the growth mode obtained by dosing Borazine at high temperatures.
We present a study of the electronic structure of a hexagonal boron nitride (h-BN) monolayer on Cu(111). Epitaxial growth is confirmed by X-Ray photoelectron spectroscopy (XPS) and diffraction (XPD), and ARPES reproduces the bands aligned to the vacuum level as seen on other metal substrates. A very small upwards shift of the Shockley surface state corroborates the small substrate interaction. The work function is significantly reduced from 4.9 eV to 4.1 eV, but 2PPE measurements show that the Cu(111) image potential state energies are barely changed. However, we expect a significantly longer lifetime due to the reduced work function, as has been observed for other dielectric monolayers on copper.
We have been studying various Dirac materials including topological insulators based on atom-surface scattering: A sensitive method to determine the electron-phonon coupling[1,2], while lineshape broadening upon inelastic scattering allows to follow the nanoscale-nanosecond motion of water at Dirac materials[3,4].
Furthermore, we will discuss the growth of hexagonal boron nitride (hBN)[5] based on real-time investigations of the structures during chemical vapour deposition. We illustrate that a precursor structure precedes the growth at lower temperatures and an additional phase co-exists with h-BN at higher temperatures - thus shining light on a largely unexplored area considering the growth of 2D materials.
Layered silicate minerals, so-called phyllosilicates, were recently proposed as naturally occuring sources of 2D van der Waals (vdW) materials. Iron-rich members of the phyllosilicate family, were previously investigated for their magnetic properties and exhibit long-range magnetic ordering. However, probing the magnetism of 2D vdW magnets, especially in the monolayer limit, is challenging. To determine their magnetic response, we performed Magnetic Force Microscopy on mono- and multilayer flakes of several iron-rich phyllosilicates prepared on SiO2/SiO-substrates. By executing these measurements in external magnetic fields, we were able to semi-quantitatively measure the magnetic response of these materials in dependence of the applied field down to the monolayer limit.
Transition metal dichalcogenides (TMDs) have revolutionised the field of electron layers, their spin orbit coupling (SOC) allowing an efficient control of the response in ,,spintronic'' applications. The band deformation induced by graphene's intrinsic SOC, though comparatively small, significantly influences the excitations. The resulting particle-hole bands cause the rapid Landau damping of plasmons, long-lived outside these regions. For specific SOC tunings achievable via adatoms and electric fields, we predict an additional collective mode above the ,,standard'' (charge-density) intraband plasmon.
We report on a low temperature (T=5K) measurement of striking singlets or multiplets of dissipation peaks above graphene nanodrums surface. The stress present in the structure leads to formation of few nanometre size graphene wrinkles and the observed dissipation peaks are attributed to tip-induced charge states transitions in quantum-dot-like entities. The dissipation peaks strongly depend on the external magnetic field (B=0T-2T). The magnetic field induce Peierls phase that shift the peaks to lower energy. At large magnetic field this shift induces the vanishing of the peaks.
Nonlinear nanoscale optics, a success story driven by ultra-short laser pulses of immense power, commonly invokes surface plasmons, highly sensitive to details of the tightly confined electric field. Intrinsically 2D materials like graphene or so-called TMDs additionally offer gate-tunability of their nonlinear response.
We develop the spectral representation of $n$th order response functions in general, then focus on the cubic longitudinal density response of charge carriers in semiconductor heterostructures. Depending on the perturbing signal, collective and single-particle modes give a rich spectrum displaying multifaceted frequency mixing. We further discuss spin-/valley-polarized systems, relevant in plasmonics, and give preliminary results for graphene.
Graphene nanoribbons (GNRs) synthesized with bottom-up technique allow electronic bandgap tuning, making GNRs an interesting candidate for room temperature switching applications as field-effect transistors (FET). We investigated various densities of aligned GNRs (by scanning tunneling microscopy) followed by transferring them to a target substrate. To investigate GNRs degree of alignment, Raman polarization anisotropy was used, which showed significant change in alignment for low GNR density samples. In this contribution, we will also discuss a modified fitting method for Raman polarization in which additional parameters are introduced to elucidate the effect of GNRs density on the degree of alignment.
Graphene nanoribbons (GNRs) with zigzag edge segments are able to host unpaired spins, which may exhibit topological end states via the interaction with superconductivity. Due to the need for a clean method to introduce superconductivity to GNRs, we propose to grow atomically precise GNRs via Ullmann coupling on the superconducting Ag/Nb(110) substrate. Through the investigation with scanning probe microscope at 4.7K, we show successful synthesis of different carbon-based configurations using only one type of molecule precursor, and confirm the proximity-induced superconductivity on these structures. We believe our results provide a new approach to study the interplay between GNR topology and superconductivity.
Quantum emitters forming nanoscopic polygon shaped arrays posses sub-radiant states with an exciton lifetime growing exponentially with emitter number. Placing an extra resonant dipole as absorber at the ring center creates a highly efficient single photon antenna. Interestingly for exactly nine emitters in a nonagon, as it appears in a biological light harvesting complex LHC2, we find a distinct minimum for its most dark state decay rate and a maximum of the effective absorption cross section, surpassing that for a single absorptive emitter. The dark state has dominant center occupation facilitating efficient energy absorption and fast transport. The ring concentrates incoming radiation a the centerand minimizes transport loss and time.
Semiconductor quantum dots are bright, on-demand single photon sources to realise quantum communication devices. An important requirement to realise such devices is the high-fidelity preparation of the biexciton state since the subsequent radiative decay produces entangled photon pairs. Although resonant excitation to the biexciton state has been successful, its sensitivity to the excitation intensity fluctuations and transition dipole moment calls for a robust preparation scheme. Here we demonstrate adiabatic rapid passage with chirped picosecond laser pulses in GaAs/AlGaAs quantum dots at 4K, and show the high fidelity generation of biexcitons, supported by theoretical simulations. Our results pave the way for utilizing quantum dots as sources of deterministic time-bin entangled photons.
We present resonant tunneling diodes, which feature intersubband transitions that are strongly-coupled to the cavity field. By using double-metal cavities with different resonant frequencies we show the infamous avoided-crossing property of the intersubband polaritons.
Resonant tunneling diodes are ideal systems for investigating resonant electronic transport in systems, which are strongly-coupled to the light field. We find that by applying different current densities, we can modulate the coupling-strength of the hybrid system.
Optical antennas have been widely used for manipulating light-matter interactions at the nanoscale in order control the emission intensity and directivity of single molecules. However, to date, precisely controlling the interaction between molecules and antennas at the single level is still challenging. In this contribution, we exploit the DNA origami technique to self-assemble ultra-compact antennas based on two gold nanorods using a T-shaped host structure. These antennas are capable of directing the emission of single fluorophores placed in vicinity of the tip of one nanorod with nm precision.
Nonlinear optical processes are widely used in quantum communication and computation, as well as laser engineering. In particular, difference frequency generation can be utilized to erase spectral distinguishability between single photons or generate laser light in otherwise hard to reach wavelength regimes. In this work, we present an AlGaAs Bragg-reflection waveguide with an embedded AlInGaAs quantum dot laser. By setting the temperature of this microscopic device, we allow for phase-matching between the internal laser emission and the interacting light in the telecom wavelength range. With an external, tunable telecom laser we investigate the generated photons from 1540$\,$nm to 1630$\,$nm and determine a nonlinear conversion efficiency of 0.64(21)$\,$%/W/cm$^2$.
We explore the evolution of the electronic spectrum of potassium compounds isolated in helium droplets from single atoms and molecules up to nanosized clusters, using a novel combination of experimental methods. The employment of a time of flight mass spectrometer enables the spectroscopy of atomically precise potassium clusters up to K110. Spectra for larger clusters within a selected size range are also recorded, revealing insight into the properties and growth of potassium nanoparticles in helium droplets. While small molecules exhibit multiple distinct spectral features, a collective resonance emerges at about 640 nm in the spectra of larger clusters. With increasing cluster size, the resonance continuously shifts towards the blue.
Semiconductor lasers with ultra-low thresholds and minimal footprints are of great interest. For high-reflectivity-coated ridge-lasers, a low threshold can only be achieved by suppressing the diffraction losses arising at laser facets. We show that, counter-intuitively, opening a carefully designed aperture in a metallic facet coating can simultaneously enhance both its transmission and modal reflectivity by phase-front correction at subwavelength scale. Simulations and experimental results demonstrate a reduction of optical mirror loss by 40% while the transmission is increased by four orders of magnitude. Applying this approach to both facets of a short-cavity quantum cascade laser, we achieve laser operation at room temperature with an electrical dissipation of only 143 mW.
High harmonic generation in a noble gas target is the most common method for table top generation of coherent XUV light. We discuss the recent progress and perspectives of high harmonic generation driven directly inside the cavity of an ultrafast thin-disk laser oscillator. Our laser system operates at a record high intracavity performance of any laser oscillator with > 1 GW of peak power, > 1 kW of average power and < 100 fs pulse duration at 17 MHz repetition rate. The XUV yield amounts to ~10 µW of average XUV power in a single harmonic order at 25 eV.
In my talk I will present recent advances in designing tailor-made states of light with optimal properties in scattering across highly disordered media. First, I will discuss how the concept of Fisher information allows us to distill from the measurable scattering matrix of a system the unique state of light, which delivers the maximum amount of information about a desired system parameter of interest to an external observer [1]. In a second part, I will discuss so-called "scattering-invariant modes”; these light fields have the unique property that they are transmitted across a disordered medium with the same output profile as when travelling through free space [2]. Both of these concepts were recently implemented together with the group of Allard Mosk in Utrecht using optical wave-front shaping tools.
Coherent backscattering (CB) of waves by a random medium provides convincing evidence of interference effects despite disorder and multiple scattering. The CB is manifested as an enhancement in the angular distribution of the backscattered intensity. In this presentation, I will present results on the effects of a vorticity filament on the CBC. Using ultrasonic waves in a reverberating cavity, we experimentally show that the discrete number of loops of acoustic paths around a pointlike vortex located in the cavity drives the cancellation and the rebirth of the CB. The vorticity filament behaves, then, as a topological anomaly for wave propagation that provides new insight between reciprocity and weak localization.
Honeybees use alarm pheromone to recruit bees into mass stinging of large predators. This pheromone is carried on the stinger, hence its concentration builds up during the attack. We investigate how bees react to different pheromone concentrations, and how this evolved response-pattern leads to better coordination at the group level. We present an experimental dose-response curve to the alarm pheromone and apply Projective Simulation to model bees as artificial learning agents that rely on the pheromone concentration to decide whether to sting. Individuals are rewarded based on the collective performance, emulating natural selection in these complex societies. We are able to identify the selection pressures that shaped the observed response-pattern.
Based on measurements from the Meteosat geostationary satellites we model the surface UV radiation in the Alps. Clear sky UV radiation depends on the solar elevation, ozone and aerosols, and, specifically relevant for the alpine regions, altitude and surface albedo. Using a radiative transfer model, measurements of visible to infrared wavelengths are used to gauge the change in surface UV radiation due to clouds. With this algorithm, we produce a near-real time surface UV and albedo map for the Alps at a 0.05° resolution. We compare our results with measurements from the Austrian UV network and partner institutions (19 stations), with a specific focus on the challenging influence of albedo.
Optical frequency combs refer to the emission of perfectly periodic waveforms of light. These waveforms can be formed due to optical nonlinearities that provide the coherent coupling of the amplitude and phase of the light. We show that Bloch gain serves as the physical origin of the linewidth enhancement factor and that it plays an essential role in the formation of quantum cascade laser combs. We develop a laser master equation to self-consistently include the Bloch gain. Our results explain the generation of self-starting combs in Fabry-Perot QCLs, and the emission of localized structures in ring resonators, akin to dissipative Kerr solitons.
Mid-infrared dual-comb spectroscopy is emerging as powerful tool for broadband and high-speed molecular spectroscopy. Chip-scale frequency combs based on quantum cascade lasers (QCLs) have become an invaluable technology, because they are electrically pumped, have a small footprint and offer an unrivalled power per mode. However, the mutual drift of both combs over time limits the averaging time and thus the sensitivity. Here, we show that two QCL frequency combs can be fully synchronized by optical injection locking. A passive optical filter enables an optical link between the combs, which locks their offset frequencies and establishes phase-coherence. Hence, the achieved signal-to-noise ratio is enhanced by more than an order of magnitude.
Dual comb spectroscopy using Quantum Cascade Laser (QCL) frequency combs, is a widely applied technique for identification of optical absorption features in the radio-frequency (RF) domain. Temperature fluctuations and electronic noise lead to often highly unstable heterodyne beating signals, hindering reproducible evaluation and analysis. We present a simple, yet reliable phase locking technique based on a dual feedback Optical Phase Locked Loop (OPLL), enabling locking bandwidths above 600 kHz for a heterodyne QCL frequency comb setup. A simplified theoretical model is applied to estimate the required parameters for the loop filters relying on a single measurement of the frequency modulation sensitivity of one frequency comb.
The linewidth enhancement factor (LEF) is known as an important property of semiconductor lasers. Recently, it is gaining more interest due to its key role in frequency comb operation. However, as of yet existing techniques to measure the LEF are limited to sub-threshold bias or single-mode operation. Here, we introduce a novel and universally applicable method to directly obtain the spectrally resolved LEF of a running laser frequency comb. The technique utilizes a phase-sensitive single shot measurement scheme. We derive a theoretical model, which is investigated by extensive Maxwell-Bloch simulations and demonstrated in an experiment on a quantum cascade laser.
We present our recent results on the impact of intersubband absorption in the valence band on the performance of interband cascade lasers (ICLs). We observe a clear performance dependence on the thickness and composition of the Ga$_{1-x}$In$_x$Sb hole-quantum well (QW), reflecting in the characteristic temperature $T_\mathrm{0}$ as well as the threshold current density $J_\mathrm{th}$. By careful design of the active W-QW the intersubband absorption in the valence band can be tailored and even completely avoided, allowing us to enhance ICL performance outside of the sweet spot 3-4 μm region, paving the way towards higher cw operating temperatures and output powers.
We present a planarized Y-coupled double metal waveguide THz quantum cascade laser. The low-area waveguide geometry is obtained via inverse design, and the device features broadband emission over 1 THz, a low threshold current, and frequency comb operation. Far-field measurements reveal characteristic interference patterns, a signature of equal power splitting and broadband phase locking of the two Y-coupled waveguide arms.
The large ZnO LO-phonon energy reduces the thermally activated LO-phonon scattering, showing great potential for improving the temperature performance of THz quantum cascade lasers. Here, we report the observation of THz intersubband electroluminescence from ZnO/MgxZn1–xO quantum cascade structures grown on a nonpolar m-plane ZnO substrate up to room temperature. The electroluminescence spectrum shows a line width of ∼20 meV at a center frequency of ∼8.5 THz at 110 K, which is not accessible for GaAs-based quantum cascade structures because of the reststrahlen band absorption. This result demonstrates an important step toward the realization of ZnO-based THz quantum cascade lasers.
By engineering the dispersion of the cavity, we observe the formation of bright dissipative Kerr solitons in the mid-infrared range. The soliton formation appears after an abrupt symmetry breaking between the two lasing directions of the ring cavity. The pump field of the soliton is generated by direct electrical driving and closely resembles the soliton Cherenkov radiation observed in passive microcombs. Two independent techniques shed light on the temporal waveform of the solitons and confirm a pulse width of approximately 3 ps. Our results extend the spectral range of soliton microcombs to mid-infrared wavelengths and will lead to integrated, battery driven and turnkey spectrometers in the molecular fingerprint region.
Quantum Cascade Detectors (QCDs) utilize the conduction band offset (CBO) of materials to create quantum confined electron states in the well material. The lattice-matched InAs/AlAs0.16Sb0.84 material system shows a large CBO of 2.1 eV at the Γ-point. This material system is therefore a candidate for the design and growth of short-wavelength mid-infrared QCDs. However, InAs has a narrow bandgap of 0.35 eV, which corresponds to an absorption in the InAs substrate for all wavelengths below 3.5 µm.
In the present study we present a lattice-matched InAs/AlAs0.16Sb0.84 QCD grown by molecular beam epitaxy lattice-matched to an n-type InAs substrate. It features an above-bandgap absorption wavelength of 2.7 µm.
Replacing 193 nm UV-radiation, extreme ultraviolet (EUV) radiation of 13.5 nm wavelength has entered commercial microelectronics production. Further progress and novel applications like microscopy of biological specimens require a further reduction of the wavelength to the sub-10-nm range (“Beyond EUV” - BEUV), e.g. the water window (2.33 nm to 4.4 nm). In this wavelength range multilayer mirrors are used instead of refractive optical components, e.g. alternating Cr/Sc structures at 3.12 nm. Their reflectivity spectra are far narrower than emission spectra of BEUV sources. In a numerical study we use grading of the layer thicknesses to widen the reflectivity spectra to collect more of the radiation and increase the optical throughput.
We present a combined analysis of low energy precision constraints and LHC searches for leptoquarks which couple to first generation fermions. Considering all ten leptoquark representations, we study at the precision frontier the constraints from $K\to\pi\nu\nu$, $K\to\pi e^+e^-$, $K^0-\bar K^0$ and $D^0-\bar D^0$ mixing, as well as from experiments searching for parity violation (APV and QWEAK). We include LHC searches for $s$-channel single resonant production, pair production and Drell-Yan-like signatures of leptoquarks. Particular emphasis is placed on the recent CMS analysis of lepton flavor universality violation in non-resonant di-lepton pairs. The excess in electron events could be explained by $t$-channel leptoquark contributions without violating other bounds.
One of the most minimal and most studied extensions of the Standard Model of particle physics is the $Z'$ boson. The LHC bounds on $Z'$ bosons that couple to quarks are very strong, models involving leptophilic $Z'$ bosons are, however, much less constrained.
We perform global fits to leptophilic $Z'$ models, putting bounds on the $Z'$ couplings to leptons, and show correlations between flavour observables in simplified scenarios. In the case where $Z'$ bosons only couple flavour off-diagonally to muons and taus, we can explain the $(g-2)_\mu$ anomaly, as well as the hints for lepton flavour universality violation in $\tau \to \mu \nu \nu$.
The new results by the Fermilab g-2 Collaboration have consolidated the long-standing discrepancy between the Standard Model (SM) prediction and the experimental measurement of the muon anomalous magnetic moment, which is traditionally considered a harbinger for New Physics. I will discuss one specific part of the SM evaluation, namely the hadronic light-by-light contribution (HLbL), which is responsible for a sizeable part of the theory uncertainty. I will present a model-independent method which incorporates all available constraints at low and high energies to obtain a more precise estimate. Our numerical analysis allows us to identify what additional information is needed to further improve the SM prediction of the HLbL.
The estimated error of the standard model prediction for the anomalous magnetic moment of the muon comes almost exclusively from hadronic vacuum polarization and hadronic light-by-light scattering, where the latter is dominated by exchanges of neutral pseudoscalars and axial vector mesons. Using holographic QCD we are able to calculate these contributions and to solve the problem of most phenomenological models to satisfy the known short-distance constraints of the hadronic light-by-light tensor, in particular the one implied by the axial anomaly pointed out by Melnikov and Vainshtein.
Particles decays with muons coming from a virtual photon in the final state are theoretically promising. In particular the discarding of helicity suppression for such channel is an advantage for leptonic flavour universality (LFU) testing in very rare $b$ hadron decay modes. The abundant channel $B^+\rightarrow K^+J/\psi\gamma^*(\rightarrow\mu^+\mu^-)$ can be studied with the available dataset at the LHCb experiment. The search is done with a centralized selection made on $J/\psi\rightarrow \mu^+\mu^-$ to explore offline reconstruction capabilities for a soft muon pair. Emphasis is brought on the study of the associated fully and partially reconstructed misidentified background. The knowledge on handling these soft muons is crucial for future exploration at LHCb.
A long standing tension between measurements of the CKM matrix element $V_{\rm ub}$ in inclusive and exclusive semileptonic decays could be due to new physics.
By using data from the LHCb experiment, we are performing a measurement of $V_{\rm ub}$ from the decay $B^{+}\rightarrow\rho^{0} \mu^{+} \nu_{\mu}$. This talk will focus on the steps toward extracting the signal yield from data. This involves the development of a multivariate algorithm used to separate signal and background, identifying and modelling important background processes and developing a stable fit of the signal and background components. Finally the future steps and challenges of the analysis will be discussed.
The photon polarisation in $b \rightarrow s \gamma$ transitions is predicted to be predominantly left handed in the Standard Model. Contributions from New Physics processes could significantly enhance the right-handed component. The $B \rightarrow K \pi \pi \gamma$ decay is a $b \rightarrow s \gamma$ transition and is sensitive to the polarisation of the photon through interference between the amplitudes describing the resonances of the $K \pi \pi$ system. We present the status of an amplitude analysis to measure the photon polarisation in $B \rightarrow K \pi \pi \gamma$ decays for the first time using data collected by the LHCb experiment between 2011 and 2018.
Recent measurements of $B$-meson decays show a consistent pattern of tensions between measured observables and Standard Model (SM) predictions. These tensions are referred to as the flavour anomalies. To understand the source of these anomalies, measurements of $b\to$$s\tau^{+}\tau^{-}$ processes are paramount, as many New Physics explanations favour enhancements in this mode. Of particular interest is the decay $B^0$$\to$$K^{*0}\tau^+\tau^-$. Reconstructing tau final states is however challenging and no measurement of $\mathcal{B}(B^0\to$$K^{*0}\tau^+\tau^-$) has been made to date. This talk/poster outlines a novel approach to measuring $\mathcal{B}(B^0\to K^{*0}\tau^+\tau^-)$ via the non-local double-loop process $B^0$$\to$$K^{*0}\tau^+\tau^-(\to$$\mu^+\mu^-)$. The analysis strategy is outlined, including the expected sensitivities to $\mathcal{B}(B^0$$\to$$K^{*0}\tau^+\tau^-)$ using this approach.
The discrepancy between the FOPT and CIPT approaches for the hadronic tau decay rate is a debated subject and constitutes the major theoretical uncertainty for strong coupling determinations. We show that the discrepancy can be analytically understood since the Borel representations for FOPT and CIPT do not agree. This implies that the OPE corrections are different for both approaches and that the discrepancy may be reconciled. Spectral function moments where the discrepancy does not arise can be constructed. We show why the FOPT and CIPT Borel representations differ and demonstrate that that differing asymptotic behavior of the FOPT and CIPT perturbation series can now be described (and controlled) analytically.
The coherence properties of an atom or superconducting qubit strongly depend on the electromagnetic environment. In waveguide QED the qubit is strongly coupled to a continuous mode spectrum, thus it decays rapidly. Collective effects between multiple qubits can be utilized to generate subradiant states that decouple from the dissipative waveguide environment.
In our experiment we strongly couple two pairs of transmon qubits to the fundamental mode of a rectangular waveguide. We show that the decay of the dark state is strongly suppressed, exceeding the waveguide-limited lifetimes of individual qubits by two orders of magnitude. Our experiment presents a step towards implementations of quantum many-body simulations in open quantum systems.
We introduce a previously unidentified paradigm for the direct experimental realization of excitation dynamics of three-dimensional networks by exploiting the hybrid action of spatial and polarization degrees of freedom of photon pairs propagating in coupled waveguide circuits with tailored birefringence. The photons exhibit Hong-Ou-Mandel-like interference simultaneously in both degrees of freedom. In a cubic graph, their interference pattern follows a recently predicted suppression law, imposed by the graph’s underlying symmetry. Moreover, the presented platform can serve as a testbed for the experimental exploration of multiparticle quantum walks on complex, highly connected graphs, suggesting a route towards exploring the dynamics of fermions in integrated quantum photonics.
In the near future, molecular simulations will be aided by quantum computer-assisted calculations which have the potential to target systems intractable for classical computers. However, since the resources offered by near term quantum computers are still limited, it is necessary to investigate hybrid quantum-classical computational schemes. In our recent work (J. Chem. Phys. 154, 114105, 2021), we rapidly scaled up such quantum-assisted simulations by means of embedding the quantum electronic structure calculation into a classically computed environment at the DFT level of theory. In this talk, I will present an extension of our work, interfacing the open source framework for quantum computing, Qiskit, with the highly parallelized classical code CP2K.
Experimental investigation of quantum mechanics with heavy objects (>m_planck~20µg) has not been achieved. It requires the combination of decoupling the quantum object from environmental influences, while remaining high control of it, a challenge increasing with the mass of the object.
To achieve these, we implement the approach of superconducting microspheres in a magnetic field trap, allowing for a mass independent levitation. To reach sufficiently high coupling rates we inductively couple the mechanical motion to superconducting circuits to enable quantum states of motion in a completely new regime of masses.
In my talk I will discuss prospects and challenges of the envisioned approach along with the current status of our experiment.
Advances in quantum information processing and technologies lead to promising developments towards a quantum network. The latter would feature local quantum processors exchanging information and entanglement via quantum links, enabling, for instance, long-distance quantum communication. The focus of this contribution is to investigate quantum correlations in networks from the point of view of entanglement. We will discuss the possibilities and limitations for entanglement generation, given the constraints of the network topology. We discuss networks featuring independent or classically correlated sources, and derive conditions for a quantum state to be preparable in the network. This shows that network structures impose strong and nontrivial constraints on the set of preparable quantum states.
We present progress on an experimental setup in which we aim to implement two-dimensional ion-crystals in a Paul trap. We will use novel optical microtraps to manipulate the phonon spectrum of the crystal. This in turn allows us to engineer the spin-spin interactions. In particular, the pinning of a single ion can be used to create short-range spin-spin interactions. In 2D crystals, this can be used to quantum simulate spin Hamiltonians on a kagome lattice, which, at low energies, are described by emergent gauge fields. Combining addressed ion operations with phonon-mode engineering, it should be feasible to equip the quantum simulator with a complete set of operations.
This talk will discuss the stability of symmetry protected topological (SPT) order under noisy channels. It has been shown that SPT order is destabilized by simple models of noise, collapsing the classification of SPT phases into a single trivial phase, even if the noise is symmetric in the usual sense. We introduce a stronger symmetry condition on channels that ensures that they preserve SPT order.
We investigate scalable surface ion traps for quantum simulation and quantum computing.
We developed a micro-fabricated surface trap consisting of two parallel linear-trap arrays with 11
trapping sites each.
We demonstrate trapping and shuttling of multiple ions, and form square and triangular ion-lattice configurations with up to six ions.
We characterize stray electric fields and measure ion heating rates between 131(13) and 470(50) phonons/s in several trapping sites[1].
Furthermore, the design of the trap array allows for tuning of the inter-ion
distance across the lattice, which we will use to demonstrate motional
coupling of ions in neighboring sites.
[1]Philip C. Holz et al., Adv. Quantum Technol. 3.11 (2020)
Quantum information experiments are advancing rapidly with realisations of real-time quantum error correction [1], demonstrations of variational quantum computing, for example, in metrology [2], and explorations of novel topological phases [3]. Underpinning these advancements is the requirement for high fidelity gates with low and uncorrelated errors between gates and qubits [4]. However, as machines are scaled up in both the number of qubits and algorithm length, it becomes increasingly challenging to keep error rates low in hardware alone.
Quantum control enables the suppression of errors to a level that exceeds limitations set by physical hardware when using primitive gate implementations. I will demonstrate the identification, reduction and homogenisation of errors across a qubit register, reducing overhead and pre-conditioning the system for quantum error correction. In addition, I will identify potential applications of these techniques in current quantum information experiments.
Cu2O, a natural p-type semiconductor with a direct bandgap of 2.17 eV, has a conventional conduction band position slightly above the water reduction potential and offers a low-cost photocathode for unassisted water splitting devices . Overlayers of n-type Ga2O3 can be employed to reduce the interfacial recombination effects due to the adequate conduction band alignment with Cu2O, leading to an increase in photovoltage. In this work we investigate the electronic properties and the morphology of surfaces and interfaces of UHV-grown Ga2O3 on Cu2O(111) with surface science methodology. In particular, we study the effect of post-annealing treatments and the influence of a reconstruction of the Cu2O(111) substrate prior to Ga2O3 deposition.
Polarons strongly influence the catalytic activity of transition metal oxides. The study of polaron formation and dynamics is fundamental to understanding the actual mechanisms and yields of catalytic reactions in these materials. A new method for the investigation of electron and hole polarons is demonstrated. Charge carriers are injected with the AFM tip into natural and Ti-doped $α-Fe_2O_3(1\overline{1}02)$. These carriers form a cloud of trapped charges, which expands due to electrostatically and thermally activated polaron hopping. Annealing of the sample and characterization by KPFM provides information on polaron dynamics; these results are compared to KMC simulations and the dependence of the hopping activation energy on the Ti doping is shown.
Pt-based catalysts are among the most efficient catalysts for the hydrogen evolution, photocatalytic and CO-oxidation reactions. However, the high cost of Pt and its susceptibility to CO poisoning are major drawbacks. Downsizing catalyst to single atoms is an effective way to reach maximum efficiency. Nevertheless, stabilization of single atoms without compromising catalytic activity is a key challenge.
Here, we present a study of the thermal stability and CO-induced mobility of single Pt atoms at the α-Fe2O3(11 ̅02) surface. Thermally induced and CO-induced sintering of the Pt single atoms are traced using STM and XPS. Also, mobility and rearrangement of adatoms have been determined with varying CO pressure in the background.
Despite its high cost, rhodium is a widely applied catalyst. So-called single-atom catalysis offers an opportunity to reduce the amount of Rh required for traditional heterogeneous catalysis, and a path to heterogenize homogeneous reactions.
Using STM, nc-AFM and XPS we compare the stability of Rh adatoms on two different model supports: $\alpha$-Fe$_{2}$O$_{3}(1\overline{1}02)$ and TiO$_{2}$(110), both after metal deposition in UHV and in a $2*10^{-8}$ mbar water background. We show that the Rh adatoms on $\alpha$-Fe$_{2}$O$_{3}(1\overline{1}02)$ sinter in UHV, but are stabilized by water up to 150 °C through coordination to 2$-$3 OH ligands. In contrast, Rh adatoms on TiO$_{2}$(110) could not be stabilized above room temperature.
Identification of the local environment of a single-atom catalyst on metal oxide surfaces is crucial for understanding the reactivity and the catalytic properties. On TiO$_{2}$(110), the stability and reactivity of adsorbed adatoms is further complicated by the presence of oxygen vacancies and associated polaron charge, as both can affect the electronic structure and local geometry. In this work the adsorption of atoms are studied by density functional theory (DFT+U) and compared with our experimental results (Rh$_{1}$) and with available literatures (Au$_{1}$ and Pt$_{1}$). By investigating the most stable adsorption site, oxidation state, O vacancies and polarons our data shows that Pt and Au fill oxygen vacancies, contrary to Rh.
Indium oxide is widely used in semiconductor industry but it also displays promising performance in electro- and photo catalytic reactions. In all applications, surrounding water molecules may influence chemical processes at the atomic scale, and understanding the interaction of water with In$_2$O$_3$ is important. We focus on In$_2$O$_3$(111), which has an intrinsically large unit cell composed of a hydrophilic and a hydrophobic area. We test the reactivity of these areas by unraveling the interfacial water structures for the whole range of water coverages in UHV, from single dissociated molecules to multilayers. Even at high coverages we clearly see hydrophilicity and hydrophobicity within the unit cell, both in experiments and calculations.
Polar surfaces offer intriguing physical and chemical properties applicable in electronics or catalysis. Cleaving the KTaO$_3$ perovskite along its polar (001) plane provides a well-defined, bulk-terminated surface with KO and TaO$_2$ terminations. As-cleaved surfaces exhibit a high concentration of in-gap states; these electrons predominantly reside at the TaO$_2$-terminated parts of the surface. These electrons can affect surface chemistry, as is demonstrated for CO molecules. CO has two adsorption configurations on the TaO$_2$ termination, and the CO differs in how it couples to the excess electrons. DFT calculations indicate that CO preferentially couples to electron bipolarons.
The work was supported by FWF project P32148-N36, by GACR 20-21727X and GAUK Primus/20/SCI/009.
SrTiO3(001), a prototypical perovskite oxide surface, is a promising candidate for all-oxide electronics. Atomic configuration of a bare surface is commonly assumed to be bulk-terminated (1×1), which is far from warranted – noncontact atomic force microscopy (nc-AFM) reveals that only through ferroelectricity-assisted cleaving in ultrahigh vacuum [1], a (1×1) SrTiO3(001) closest to the pristine can be obtained [2]. Both surface terminations appear as two domains of opposite polarization. This provides dichotomous selectivity for applications, as these domains behave differently under UV illumination: while metallic TiO2 surface is unaffected, SrO termination traps excess positive charge.
[1] I. Sokolović et al. PRM 3,034407(2019)
[2] I. Sokolović et al. PRB,in print(2021)
We study the effect of antiferromagnetic buffer layers (insulating LaMnO$_3$ and metallic La$_{0.45}$Sr$_{0.55}$MnO$_3$) on the magnetism of epitaxial ultrathin La$_{0.8}$Sr$_{0.2}$MnO$_3$ (LSMO) films, grown by molecular beam epitaxy and studied by x-ray magnetic circular dichroism as a function of temperature and thickness. We find a non-monotonic variation of the moment in the LSMO films grown on LaMnO$_3$ (which display a magnetic moment) and a bulk-like moment at 5 unit cells thickness; films grown on La$_{0.45}$Sr$_{0.55}$MnO$_3$ seem to adopt the properties of the buffer layer (reduced moments). The results highlight the role of the buffer layer properties in understanding the effects of charge/spin exchange for controlling the magnetic properties of ultrathin LSMO.
The Poster Session is held on Tue and Thu. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Tue.
The predissociation spectra of the $^{35}$Cl$^-$(H$_2$) and $^{35}$Cl$^-$(D$_2$) complexes are measured at low frequencies between 400 and 800 cm$^{-1}$ in an ion trap at different temperatures. Above a certain temperature, the ligand switching between the two isotopologues $ortho$ and $para$ leads to a strong suppression of the excited hyperfine configuration. Performing the experiment below 30 K and 22 K for Cl$^-$(H$_2$) and Cl$^-$(D$_2$), respectively, we can detect the more weakly bound complexes.
Due to accurate quantum calculations, the bands in the Cl$^-$(H$_2$) complex have been assigned to the intermonomer vibrational stretching mode.
The plasma sheath mechanisms are well-known in non-magnetised plasmas, but a model for a sheath in a tilted magnetic field does not exist. In this work, we present the development of a facility to study the sheath of RF plasmas in a tilted magnetic field. We aim at characterising the sheath by determining the potential, the electron and the ion temperatures and densities. To measure these parameters, a movable planar electrostatic probe will be combined with optical emission spectroscopy. In this contribution, first probe measurements in Ar discharges under 0.5T are discussed.
Drift wave turbulence occurs ubiquitously in inhomogeneous magnetised plasmas, and determines transport in magnetic fusion experiments. The quasi two-dimensional turbulence implies an inverse energy cascade that condensates in persistent zonal flows, which correspond to a global sheared rotation in a torus. We study bifurcation from turbulence to flow regimes by simulations with a gyrofluid Hasegawa-Wakatani model when dissipative coupling as control parameter is increased. In addition to previous fluid models, our gyrofluid simulations include finite Larmor radius (FLR) effects for a temperature ratio tau = Ti / Te > 0. We discuss changes in transition characteristics related to FLR effects, and conditions for hysteresis in the back transition.
Gyrokinetic and gyrofluid models for magnetised plasmas evolve gyrocenter densities ne and ni of electrons and ions, that are coupled via a polarisation equation which determines the consistent electric potential phi fulfilling quasi-neutrality. Full-f models, based on the full distribution functions f without smallness assumptions of a Bousinesq approximation, use polarisation equations in the form "div [ ni grad phi ] = Q" of generalised Poisson equations. For efficient computation of phi(x) from spatial functions ni and Q(ne,ni), many numerical models impose approximations. We study effects of different common linearisation approximations to the polarisation equation by simulations of fusion plasma edge turbulence with a thermal full-f gyrofluid model and code.
Localised pressure perturbation "blobs" of plasma in a magnetic field with a field gradient grad B perpendicular to the field direction experience an interchange instability. The resulting propagation of a blob down the field gradient is similar to the Rayleigh-Taylor instability in neutral fluids, and contributes to intermittent losses in the outer scrape-off layer of fusion plasmas. We study blob acceleration, propagation and nonlinear break-up by simulations with a thermal full-f gyrofluid model for various experimentally relevant initial conditions of the blob pressure, with different combinations of positive or negative density and temperature perturbations, such as hot density blobs with increased temperature, or cold density blobs with locally decreased temperature.
The ASACUSA collaboration at CERN aims to perform a ppm measurement of the ground-state hyperfine structure of antihydrogen. Due to the Long Shutdown 2 no antiprotons are provided by CERN. For this reason, a proton source was developed to produce hydrogen by mixing electrons and protons in the same apparatus and with the same techniques which will be used for the antimatter experiment.
The poster will cover the design, the method of operation, as well as results of the proton production.
The combination of crossed beams with kinematically complete velocity map imaging is a powerful tool to obtain experimental insight into reaction dynamics. The obtained differential cross sections can be linked to atomistic reaction mechanisms. We are investigating reactive scattering of CH$_3$I with atomic oxygen anions. Energy dependent experiments ranging from 0.4 eV to 2 eV relative collision energy revealed four reaction pathways with different atomistic mechanisms. Here we report recent results on the reaction of a radical anion reaction: O- reacting with CH$_3$I. We discuss energy-dependent differential cross sections and branching ratios for four observed, competing reaction pathways.
The iron hydride cation (FeH+) is believed to be an abundant transition metal compound in the interstellar medium (ISM). Due to the lack of laboratory data, it has not been identified in spectral observations. We performed infrared multiple photon dissociation (IRMPD) spectroscopy of FeH+ tagged with two argon atoms. The Fe-H stretch in Ar2FeH+ is observed at 1854 cm-1, and two weaker combination bands appear around 2000 cm-1 and 2080 cm-1, respectively, in agreement with quantum chemical calculations. The Ar-Fe-Ar bending mode is populated at the temperature of the experiment, most likely causing the observed broadening of the Fe-H stretch.
Proton transfer reactions (PTR) are a useful means to detect volatile organic compounds in the atmosphere. By replacing the commonly used H$_3$O$^+$ with N$_2$H$^+$ or ArH$^+$ as the primary ion, an additional range of molecules becomes accessible for protonation, making PTR suitable for ultra-high purity (UHP) gas analysis.
Utilizing Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry, reaction kinetics of N$_2$H$^+$ and ArH$^+$ with O$_2$, H$_2$O, CH$_4$, NO$_2$, CH$_3$OH, and C$_3$H$_6$O are recorded and reaction rate constants derived, revealing efficient proton transfer to the probed substances. This is in agreement with the proton affinities from quantum chemical calculations.
In force spectroscopy of chemical bonds, single molecule chains are being stretched using an atomic force microscope (AFM). Strong surface anchors are required to address covalent bonds. Here acid chloride anchors are tested, featuring a very reactive functional group. Rupture force and rupture length of stretched polyethylene glycol was measured. The slope of the force curves is used to derive the elasticity of the molecule, which in turn yields the length and thus the molecular weight distribution for the stretched molecules. A comparison with the molecular weight distribution provided by the manufacturer shows that indeed polyethylene glycol molecules are stretched.
Plasma Fireballs are luminous, sharply defined, quasi-spherical plasma objects, which ap-pear in the vicinity of a positively biased electrode placed in background plasma, existing in both stable and dynamic states where a periodic expulsion and backflow of ions near the sheath edge is observed generating oscillations in the range of 20 kHz. In this work we present results on the study of the interactions between three independently biased fireballs. The distance between the electrodes, along with the background pressure, af-fects the recorded current oscillations. Comprehensive investigations of the frequency behaviour were carried out for different electrode voltages, at several background pres-sures and variable electrode distances.
The gas-phase photophysics of complex biomolecules enable us to understand the intrinsic structural and functional properties without solvent influence. The photodetachment and photodissociation of deprotonated 2’-deoxyadenosine-5’-monophosphate anion (dAMP–), a monomer of DNA, contribute to its intrinsic photoresponse, fragmentation channels, and the associated lifetimes. We report on the status of photodetachment and photodissociation measurements of dAMP– with UV laser light as a function of wavelength from 210 - 280 nm. The study is carried out by confining the anions generated from electrospray ionization, in a cryogenic 16-pole wire trap maintained at 2.9 K by buffer-gas collision.
The Poster Session is held on Tue and Thu. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Tue.
Dihydrogen halide clusters are the subject of various theoretical and experimental studies. In their anionic state they are weakly bound complexes and can provide insight into dynamical processes in chemical reactions. Here we report the three-body reaction rate of Cl$^-$ with H$_2$ forming the Cl$^-$(H$_2$) complex, as well as the temperature dependence of this reaction in the range of 10 – 30 K. Furthermore, we observe the back-reaction with an unexpected density dependence to the third power. Comparisons of the experiment in a 22-pole rod and 16-pole wire radiofrequency ion trap are presented and show that the ions reach lower temperature in the 16-pole trap.
Experimental observation of state-to-state interactions, here specifically reactive encounters of ions and molecules, requires both precise control of the initial conditions and sufficient resolution of the product states. We have designed and simulated a new crossed beam velocity map imaging spectrometer, which exploits coincidence detection of products to push the experimental possibilities towards this goal. A high power and high repetition rate Lyman-alpha source in combination with a UV ionization laser will be used to detect neutral hydrogen atoms, which are often produced as the neutral co-product in important interstellar reactions such as H$_2^+$ + H$_2$ forming H$_3^+$ + H.
Different neutral and charged interstellar molecules constitute the building blocks for a rich reaction network in the interstellar medium (ISM). The abundance of negative ions in the ISM and their role in the chemistry of these environments has been subject to long-standing discussions in astrochemistry. Photodetachment cross-section studies are crucial for predicting the abundance of anions in the ISM. In our experiments we aim to study the threshold photodetachment spectroscopy of C2- and C2H- which are speculated to exist in the ISM, in a 16-pole radiofrequency ion trap, which can be cooled down to 6 K to mimic conditions in the ISM. The status of the experiment will be presented.
A single ring of sub-wavelength spaced dipole-coupled quantum emitters possesses only few radiant but many extraordinarily subradiant collective modes. These exhibit a 3D-confined spatial radiation field pattern forming a nano-scale high-Q optical resonator. Proven to show promising results in the single-ring case, a spin-wave Ansatz was chosen to investigate the radiation properties of double-ring structures. It has been found that the wave function is composed of two spin-waves with equal or opposite phase, allowing us to study the rich behaviour of the super- and subradiant properties of these eigenmodes and proceeding to analyse the collective eigenmodes of light-harvesting complexes in purple photosynthetic bacteria analytically.
In this work, we studied dissipative phase transitions (DPT) in optomechanical systems. We applied the stability analysis at a well-defined thermodynamic limit to arrive at the corresponding phase diagram, which exhibits two types of instability lines: soft and hard mode instabilities—directly related to DPTs. The optomechanical phase diagram shows a rich structure composed of first and second-order DPT (with and without symmetry breaking). The analysis is supplemented with the computation of critical exponents and corresponding universality class. Finally, we studied the quantum properties of the steady-state quantified via squeezing and entanglement. We demonstrate that one can boost these quantities by applying auxiliary passive linear optic operations to the steady-state.
Simulating quantum magnetism is one of the major high goals pursued currently in the field of ultracold atoms and molecules. Recently a new approach was suggested for the production of a dipolar quantum gas utilizing both electric and magnetic dipole moments. The scheme relies on exciting dysprosium atoms into a superposition of long-lived opposite-parity states near degeneracy. We have set up a compact apparatus incorporating a quantum gas microscope. The apparatus allows the use of UV optical lattices, therefore boosting the dipolar interaction and further enables the detection of spin order atom by atom. The last is crucial for establishing the complex phase diagrams of models for quantum magnetism.
The combination of quantum gas microscopy and ultracold polar molecules promises experimental access to rich new many-body physics. Our experiment focuses on achieving this using the KCs molecule. We present recent work on optical transport of ultracold atoms using a focus tuneable Moiré lens. The use of this lens makes the setup more robust, compact and stable compared to conventional methods. We will also present our exploratory work on different strategies of mixing and condensing Cs and K before association into molecules. Finally, we will give an overview of the ongoing construction and design of a new quantum gas microscope chamber.
Trapped atoms and atomic ions are among the best-controlled quantum systems which find widespread applications in quantum science. However, a similar exquisite control over molecules has remained elusive so far due to their complex energy-level structure with additional rotational and vibrational degrees of freedom. We employ a quantum-logic protocol which uses a single co-trapped atomic ion as a probe for the molecular state. Specifically, we demonstrate a quantum non-demolition state detection on N2+ with fidelities exceeding 99% without destroying the state itself. The present method paves a way for the implementation of molecular qubits, establishing new frequency standards in the mid-IR regime, and for investigating state-to-state dynamics of chemical reactions.
Molecular quantum optics deals with phenomena related to the wave nature of molecules, in particular the interaction of molecules with light. Modern molecule interferometry observes quantum effects in massive particles and more recently also biologically relevant molecules. The high sensitivity to beam shifts and wave dephasing can be used to extract a variety of molecular electronic properties. Molecular matter-wave experiments hence open a wide field of research at the interface between quantum optics and chemical physics. Complex many-body systems further offer a variety of properties that render quantum decoherence interesting and may be technologically useful for future applications.
Accurately controlling the dynamics of physical systems by measurement and feedback is a pillar of modern engineering; Achieving this in an optimal way is a challenging task that relies on both quantum-limited measurements and specifically tailored algorithms for state estimation and feedback. We demonstrate real-time optimal control of the quantum trajectory of an optically trapped nanoparticle. We combine confocal position sensing close to the Heisenberg limit with optimal state estimation via Kalman filtering to track the particle motion in phase space. Optimal feedback allows us to stabilize the quantum harmonic oscillator to a mean occupation of n = 0.56 ± 0.02 quanta, realizing quantum ground state cooling from room temperature.
We provide an argument to infer stationary entanglement
between light and mechanical oscillator based on measurement of light only. We propose an experimentally realizable scheme involving an
optomechanical cavity driven by a resonant, continuous-wave field operating in the non-sideband-resolved regime. This corresponds to the conventional configuration of an optomechanical position- or force-sensor. We show
analytically that entanglement between mechanics and
output-field of the cavity can be inferred from the measurement of squeezing in Einstein-Podolski-Rosen
quadratures of suitable temporal modes of the stationary light-field.
Squeezing can reach levels of up to 50% of noise reduction below shot-noise in the limit of large cooperativity. Entanglement persists even in the limit of small cooperativity.
We have studied how a coherent phenomenon can control the polarization rotation in the Rb vapour. Experimentally we have observed a sharp rotation spectrum in the vicinity of electromagnetically induced transparency in a V-type system. The dependencies of various system parameters have been investigated. Theoretical models have been developed to explain the observed phenomena. The observed signal can be used for optical locking purposes, in the detection of slow light, to detect the unknown polarization state of a beam, etc. Our study has importance in the various fields of application of the polarization rotation like magnetometry, birefringence lens etc.
The ASACUSA CUSP collaboration at the Antiproton Decelerator (AD) of CERN aims at a precise measurement of the ground-state hyperfine splitting of antihydrogen, which promises to be one of the most sensitive tests of CPT symmetry. A dedicated mixing trap serves as a source for in-flight spectroscopy. While antiprotons are supplied from the AD, positrons from a $^{22}$Na source are slowed down by a neon rare-gas solid moderator and accumulated in a Surko-type buffer gas trap.
We will discuss methods for producing, trapping, accumulating, and conditioning positrons. New developments in positron temperature measurement and cooling will be shown, which are important for improving the mixing efficiency for ground-state antihydrogen.
We have built an enhancement cavity able to sustain 20 watts of intracavity power in the deep-UV range (244 nanometer) on several hour time scales, in a vacuum chamber designed for muonium 1S-2S precision spectroscopy. These performance are reached when fluoride coated mirrors are in a low oxygen pressure environment ($10^{-3}$ millibar), meanwhile in higher vacuum ($10^{-8}$ millibar) up to 10 watts can stably be observed on one hour timescale. We demonstrate the superior performance of fluoride versus oxide coated mirrors on long term operation, with degradation being partially recoverable through the use of oxygen. Fluoride coatings display enhanced performance after initial conditioning with UV in an oxygen rich environment.
In commercial telecommunication and high-precision spectroscopy, single-sideband modulators are widely used for optical frequency shifting. Drifts of the bias voltages, which control the phases between the arms of the dual-parallel Mach-Zehnder modulator, require stabilization to enhance suppression of the carrier and the second sideband. Modern methods rely on the modulation of these bias voltages, resulting in residual amplitude modulation of the single-sideband. Here, we present a novel stabilization scheme that is based on dual-frequency modulation. An additional low-frequency modulation enables the generation of the sideband and carrier discriminant without affecting the amplitude of the desired sideband.
Traditional laser locking methods rely on reference sideband generation from the main carrier. A modulation-free alternative is the use of spatial modes in an optical cavity. In this poster, we present an all-passive modulation-free method of locking a laser to an optical resonator. We engineer the input beam to contain 2nd order spatial modes of a non-confocal 3-mirror cavity. This method is immune to alignment drifts compared to earlier schemes relying on small beam tilts to induce 1st order modes. We obtain an unprecedented and highly-competitive locking stability of $5 \times 10^{-7}$ fraction of the linewidth of the cavity at 10 s averaging time.
The terahertz (THz) region lies in between of the RF and optical spectral regions and is expected to become a part of novel wireless links due to its high bandwidth and safety. Therefore, a refined control over THz radiation is required.
We investigate the influence of spatially controlled, near-infrared induced charge carriers in high-resistivity silicon on a collimated THz beam. Our results indicate that the refractive index is significantly modulated. This spatially controlled modulation is especially interesting regarding phase-modulation, which may pave the way for beam-steered wireless THz links.
Bringing milligram-scale mechanical oscillators to the quantum regime for enhanced sensing is currently a very sought after goal. Prospects range from investigation of macroscopic quantum mechanics and exploration of quantum aspects of the gravitational interaction to searches of unknown (fifth) forces. Sufficient isolation and achieving quantum control have remained challenging in this mass regime. We built a 1 mg torsion pendulum and set it in a UHV chamber together with an optoelectronic feedback mechanism allowing control and characterization of the mechanical properties of the pendulum. We measured competitive quality factors for the pendulum and torsion modes, 900000 and 64000, respectively.
The competition between short-range and cavity-mediated infinite-range interactions in a cavity-boson system leads to the existence of a superfluid and a Mott-insulator phase within the self-organized regime. We quantitatively compare the steady-state phase boundaries of this transition measured in experiments and simulated using the Multiconfigurational Time-Dependent Hartree Method for Indistinguishable Particles. We reduce the computational cost by reducing the full system to a 2D four-well potential. We argue that the validity of this representation comes from the nature of both the cavity-atomic system and the Bose-Hubbard physics. The experimentally measured and theoretically predicted phase boundaries agree reasonably. We propose a new approach for the quantitative determination of the superfluid--Mott-insulator boundary.
We study fundamental effects of spontaneous emission with a mirror, which is used to couple a Ba$^+$ ion with its retroreflected fluorescence light. This back-reflected fluorescence induces a mechanical effect on the ion's motion, varying sinusoidal with the ion-mirror distance resulting in a force.
We present a method to control this force to study the effect of back-reflected light on the ion's dynamics. For control of the force an electro-optical modulator is introduced between ion and mirror to adjust the optical length and, effectively, the ion-mirror distance allowing to control the force felt by the ion. We will use the force to drive the ion motion at the trapping frequency.
We propose a new platform to investigate the interaction of antiprotons with ordinary matter at the kinetic energy of a few K or lower. We will confine antiprotons and negative ions in a Penning trap to prepare both species at low temperature within the same trapping volume. After co-trapping, the anions will be photodetached with a laser pulse to form cold neutral atoms, which will interact with the nearby antiprotons. This setup will allow us to measure the interaction of matter and antimatter as a function of time by correlating the detection events with the laser pulse and opens the door to precision spectroscopy of the antiprotonic Rydberg atoms.
Applications of lasers in quantum metrology require precise control of the laser frequency. This is usually achieved by locking the frequency of a slave laser at a tunable offset from a master laser. Here we present a new scheme for a robust and high precision laser offset frequency locking. A hybrid frequency discriminator generates an error signal that has a wide capture range of more than 150 MHz while preserving sharp resonance needed for a tight lock. The Allan deviation was measured to be less than 55 Hz at 30 seconds and remained below 1 kHz for more than 1000 seconds.
Preparing a massive oscillator near the quantum limit has become a central goal in fundamental sciences.Optomechanics, where a mechanical mode is coupled to a light field, allows to operate a mechanical object near its quantum ground state. Our setup consists out of a microwave SQUID based cavity inductively coupled to a mechanical cantilever.Despite being deeply in the unresolved sideband regime, we can use the intrinsic nonlinearity of our cavity originating from the SQUID for enhanced cooling. We demonstrate that our system outperforms an identical linear system by more than one order of magnitude.Currently we reduce the thermal population of the cantilever by a factor of 350, to around 11 phonons.
We reported depletion spectra of Rb2+ complexed with up to ten Helium atoms. The ions were formed by doping helium nanodroplets in a pickup cell filled with low-density Rb vapor and subsequent electron ionization. Two absorption bands were observed between 920 and 250 nm, due to transitions into the 12Σu+ and 12Πu states. The transitions are blue- and redshifted, respectively, when the number of He atoms is increased. Spectroscopic constants and the spin–orbit (SO) splitting are deduced for the bound 12Πu state. All experimental findings are supported by ab initio calculations, using CCSD method for modeling ground electronic state, and EOMCCSD and MRCI for electronically excited states.
The Poster Session is held on Tue and Thu. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Tue.
Nanomedicine is quickly emerging field at the interface between nanotechnology and pharmacy with even some of the COVID-19 vaccines being prime examples. However, the microscopic imaging of these new technologies is lacking behind, causing a gap between practical application and theoretical understanding. In this poster, we present the results of characterizing protamine-microRNA nanoparticles (proticles) using Atomic Force Microscopy.
Optical tweezers are a powerful tool for measuring tiny forces on the microscale. However, when multiple traps are used, it is challenging to simultaneously measure the individual forces and torques.
We present a generally applicable holographic force measurement method to recover the individual forces based on a single farfield image. As this method does not require information about size, shape, or optical properties of the particle it is well suited to study biological specimen. We demonstrate measurements for up to ten traps, and disentangle the individual forces on a red blood cell stretched by four optical traps.
In this contribution, a new experimental setup will be discussed which enables mass spectrometry and laser spectroscopy of (bio)molecular ions in a well-defined and ultracold environment. The setup consists of a helium nanodroplet (HND) source and an electrospray ionization (ESI) source in combination with a time-of-flight mass spectrometer. The ESI enables the transfer of fragile molecules from the solution into the gas phase. These molecules are then picked-up by traversing HNDs, which are transparent from the deep UV to the far IR and serve as gentle matrices to provide a cryogenic environment, reducing the number of populated quantum states and freezing out structural fluctuations of the embedded (bio)molecules.
Liquid crystal based spatial light modulators (LCoS SLMs) are widely used due to their ability to continuously modulate the phase of a light field. A common problem in these devices is the pixel crosstalk, which causes the response of the SLM to deviate from the ideal behaviour. We use detailed numerical simulations of the SLM to reproduce the measured response and model the crosstalk effect. From this rigorous simulations we develop and validate a simplified model which enables a much faster evaluation of the SLM response. We then utilize this simplified model together with numerical optimization algorithms for crosstalk compensation.
In general, 4D printing is a programmable deformation of the manufactured object over time, triggered by an external stimulus. For the sample production, a specially developed wood filament with a high sensitivity to moisture was used. Two different sample types having various print directions were designed and produced using an FDM 3D printer. As soon as the specimens came into contact with moisture, for the first type the print directions applied led to an outward curvature, while for the second type the print directions chosen resulted in an inward curvature. Once the moisture disappeared, the samples returned to their original FDM 3D printed geometry
Disulfide bonds play an important role in biology, as they can influence the conformation of proteins through the covalent connection of adjacent strands. Reversible cleavage of the bond occurs both through physiological agents and forces. It is therefore interesting to study the effects of forces on the disulfide bond in the single molecule. For this purpose, we used an atomic force microscope (AFM) to investigate specifically designed molecules, which contain safety lines with two different lengths bridging the disulfide bond. Thus, rupture of the disulfide bond can be confirmed and the necessary force measured directly at the single molecule level.
This work illustrates recent advances based on MicroScint, a technology aimed to realize a beam transverse profiler with high spatial resolution based on a microfluidic device. The active area consists in a silicon microfabricated structure filled with an organic liquid scintillator, with spatial resolution down to 30um. We also developed scintillating resin-based devices, obtained through PDMS moulds, which allows 2D tracking of particles, with spatial resolution of ~15um. The developed detectors are designed to suit all types of proton or heavy ion accelerators. The detectors can also be used for dosimetry, X-ray imaging or for fundamental physics experiments for providing a novel tool for wave function manipulation and control.
The Poster Session is held on Tue and Thu. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Tue.
A nuclear excitation following the capture of an electron in an empty orbital has been recently observed for the first time. The experiment remains particularly fascinating and unexplainable by state-of-the-art theory. So far, the evaluation of the cross section of the process has been carried out widely using the assumption that the ion is in its electronic ground state prior to the capture. We show that by lifting this restriction new capture channels emerge resulting in a boost of various orders of magnitude to the electron capture resonance strength.
The n2EDM experiment will search for the neutron electric dipole moment, to elucidate the Baryon Asymmetry of the universe.
The precession frequency of spin-polarised neutrons will be measured in a magnetic field and an electric field, in a Ramsey-type experiment.
The magnetic field will be continuously probed by a laser via the spin precession of Hg atoms in the precession chamber to account for fluctuations.
The radio frequency pulses required to flip the neutron spins relative to the magnetic field axis can affect the Hg spins, and vice versa. The application of window functions to these pulses was investigated to minimize these effects and the corresponding systematic uncertainties.
A powerful and adaptable tool for performing experiments with positrons and positronium, is a positron trap. Positrons can be confined by using magnetic and electric fields combined with Nitrogen and CH$_4$ buffer-gas. Such a device can produce ~10$^5$ e$^+$/s in bunches with a diameter of 1-2 mm and an energy spread of approximately 50 meV.
Such a trap is under construction at SMI and will be used in order to perform the first precise measurement of the binding energy of molecules containing positronium, such as PsH and PsO.
This poster will describe the progress on the development and construction of the positron trap at SMI.
How can I improve the learning success in my physics exercise class? Can I prepare an engaging lesson efficiently? Our Engaging Physics Tutoring (EPT) project addresses these questions by providing a hands-on didactical tool-box for physics teaching assistants. 13 fully worked out lessons for introductory physics as well as nuclear and particle physics lectures are available online as eBooks. They serve as an example of a widely applicable teaching concept based on advance organizer slides, multiple choice questions and an interactive “hit of the lesson”. A short pre- and a post-test monitors the learning success over each lesson. The project was supported by the ETH Zürich Rector’s Impulse Fund.
A Wien (velocity) filter for the Ion Laser InterAction Mass Spectrometry (ILIAMS) facility at the Vienna Environmental Research Accelerator (VERA) was characterized and commissioned.
First, simulations via the ion beam simulation program SIMION were done to find the best position in terms of mass separation for a Wien filter within the facility.
After installation of the Wien filter, commissioning measurements were taken with uranium fluoride and chlorine ion beams. A separation between $^{35}$Cl and $^{37}$Cl of 2.5 could be observed. First results with the much heavier uranium fluorides revealed a delicate dependence of the separation on the tuning of the ion optical elements.
We present results from a pilot study at high spectral resolution (R=100,000) of diffuse interstellar bands (DIBs) in the near-infrared J-band with VLT/CRIRES. Several so far unknown near-IR DIBs are detected. The membership to DIB families is investigated, as indication of the origin from common carriers. The DIB sightlines are characterized to unprecedented accuracy and precision due to the availability of quantitative analyses of the illuminating background stars. Peculiarities of the interstellar extinction law along these sightlines are studied.
Excellent particle detection momentum threshold, together with cost-effective scale-up prospects, make the proposed TPC, a strong candidate for reducing the systematic errors in future neutrino oscillation experiments. Thousands of photons per primary electrons are produced through a gas electron multiplier. These photons, normally in the UV range, are shifted to visible using a PEN wavelength shifter. Using a simulation that describes all the critical physical phenomena in photon transport, it is shown that hundreds of photons can be collected by a multi-photon pixel counter. Minimising optical aberrations, the number of photons per channel was demonstrated to be larger than the dark-count background, and therefore tracks can be reconstructed.
This contribution describes how the so-called Barbero–Immirzi parameter, which is akin to the theta parameter in QCD, deforms the SL(2,R) symmetries of the gravitational boundary data on a null surface. Our starting point is the definition of the gravitational action and its boundary terms. We introduce the covariant phase space and explain how the Holst term alters the symmetries on a null surface. We show that this alteration only affects the algebra of the edge modes, whereas the algebra of the radiative modes is unchanged. Finally, we compute the Dirac bracket between physical observables on an auxiliary phase space, where the SL(2,R) symmetries of the boundary fields is manifest.
The Poster Session is held on Tue and Thu. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Tue.
Magic-angle twisted bilayer graphene has received a lot of attention due to its flat bands that lead to intricate correlated phases. However, control over the system parameters of such devices is limited. We propose a single graphene sheet with adatoms periodically placed on top as an alternative system that realizes flat bands. Performing first principle calculations, we obtain realistic spectra for feasible transition-metal adatoms. Further group-theoretical analysis reveals the fragile nature of topology of flat bands. We study the bulk-boundary correspondence associated with the fragile topology of the flat bands and numerically examine the corner-localized in-gap states, which are a consequence of the filling anomaly resulting from the nontrivial topology.
2D-materials represent some of the simplest systems for the study of a variety of different phenomena, including superconductivity magnetism and other phase transitions. A prototypical 2D-system can be constructed depositing a noble gas over a substrate with a weak interaction between the two, such as graphite, to create a tunable layered crystalline structure. In this work we demonstrate how the growth process of Argon layers on graphite can be imaged and controlled using electron diffraction. The phase diagram at low-P low-T is still unknown and making possible its exploration allows us to understand which structures and phases are involved and what mechanism drives the melting process.
We analyse the dynamics and universality of Dirac and nodal loop gap closures under a continuous quench by employing the Landau-Zener formalism. We reveal that the scaling behaviour of the topological defect density can deviate from the prediction of the Kibble-Zurek mechanism when the gap closure is extended. This is also observed in the presence of multicriticality, where we recover different power laws depending on the path taken in parameter space. We further characterise this difference from topological defect generation in the form of dynamical vortex-antivortex pairs in momentum space. Our study offers new insights into the classification and detection of universality classes of topological phase transitions.
Superconductor-semiconductor hybrids are platforms for realizing effective p-wave superconductivity. Spin-orbit coupling, combined with the proximity effect, causes the two-dimensional semiconductor to inherit p ± i p intraband pairing. An external magnetic field can then result in transitions to the normal state, partial Bogoliubov Fermi surfaces, or topological phases with Majorana modes. Experimentally probing the hybrid superconductor-semiconductor interface is challenging due to the shunting effect of the conventional superconductor. Consequently, the nature of induced pairing remains an open question. Here, we use the cQED architecture to probe induced superconductivity in a 2-D Al-InAs hybrid system. We observe a strong suppression of superfluid density and enhanced dissipation driven by magnetic field, which cannot be accounted for by the de-pairing theory of an s-wave superconductor. These observations are explained by a picture of independent intraband p ± i p superconductors giving way to partial Bogoliubov Fermi surfaces, and allow for the first characterization of key properties of the hybrid superconducting system.
Poly(furfuryl alcohol) (PFA), produced through polymerization of furfuryl alcohol, is a thermosetting polymer and basis of thermoset resin systems, and it has been investigated in several studies (IR, 13C-NMR, Raman, DSC), new aspects being considered each time. The target of the present study, performed within the Interreg Italy Austria project ITAT1023 InCIMa and ITAT1059 InCIMa4, is the investigation of the presence and the grade of cross-linking and of conjugation in thermosetted PFA in comparison to the pristine, viscous PFA by using multi-wavelength Raman spectroscopy in the visible and in the ultraviolet spectral range, and additionally by Raman spectra simulations via first-principles and semi-empiric methods.
Magnetite (Fe3O4) is the first magnetic material ever discovered. At 125K, the system undergoes a metal-insulator transition (MIT) accompanied by a structural transition as well as a magnetic rearrangement, the so-called Verwey transition.
Light offers the appealing possibility of manipulating the electronic and structural properties of matter. Here, using two different photon-energies, we directly visualize the photo-induced structural dynamics of Magnetite using the ultrafast electron diffraction (UED) technique providing sub pm/ps spatio-temporal resolution. We found two distinct behaviors that could be explained by different interactions between the electronic/magnetic degrees of freedom and the crystal structure.
Dielectric-Loaded Surface-Plasmon-Polariton waveguides (DLSPPWs) offer suitable solutions to guide mid-IR light along the surface of semiconductor-based optoelectronic devices. Since the main portion of the mode in typical semiconductor-Au-Ge plasmonic layer structures is propagating outside in the surrounding medium, this geometry allows to efficiently address chemical sensing of liquids including protein solutions or solvents like isopropyl alcohol. To increase the resilience of the plasmonic-waveguides towards more aggressive analyte liquids, we investigate the impact of additional nanometer-thick high-quality protective surface films on parameters like the propagation-losses of the plasmonic mode or its confinement. We analyze low-loss long-wave mid-IR materials including Al2O3 and CaF2, typically deposited by sophisticated techniques like ALD or MBE.
Terahertz quantum cascade patch antenna lasers are a promising technology to realize surface emission in the terahertz range. The laser emission frequency can be tuned by changing the patch size and array geometry. Biasing these sub-wavelength structures requires metallic connection lines with limited effect on the patch mode.
We present epilayer-down mounted patch arrays on a substrate with low optical losses in the terahertz range. Our biasing lines run only along the substrate surface. Electromagnetic simulations show that substrate mounting of patch antennas broadens the absorption and leads to multimode operation.
In this work we present the realization of low-density polyethylene (LDPE) ridge-waveguides using spinning-deposition, standard-lithography and oxygen-plasma-etching for patterning. Parameters such as toluene-solvent concentration, spinning-speed and bake-out-process temperature in a vacuum-oven are optimized in order to obtain the required film-thickness. Ellipsometry data shows a LDPE-thickness of ~ 400-500 nm, corresponding to refractive index of 1.51 (at 630 nm). The results indicate that spin-coating with bake-out at 100oC yields the best-quality LDPE-films. Additional COMSOL-simulations display low optical losses of LDPE for the whole mid-IR spectral range. As proof-of-concept we will also present the results of optical characterization performed in the log-wave infrared to confirm the suitability of LDPE for mid-IR plasmonic-applications.
Infrared spectroscopy is a reliable tool for chemical sensing in various fields from industry over environmental monitoring to medicine. Interband cascade lasers (ICLs) have proven to be important light sources for such applications. Utilization of ring-shaped laser geometries provides a collimated beam profile as well as vertical light emission. We combine the ring geometry with the ICL technology and present the first continuous-wave ring ICL. The laser provides single-mode emission at 4.4µm, which makes it an ideal candidate for various spectroscopic applications. In addition, the relatively low power consumption of ICLs facilitates lightweight sensors for hand-held devices.
Quantum cascade lasers facilitate compact optical frequency comb sources that operate in the mid-infrared. Enhancing the optical bandwidth of these chip-sized lasers is important to address their application in broadband high-precision spectroscopy. We provide an investigation of the comb spectral width and show how it can be optimized to obtain its maximum value. The interplay of nonoptimal values of the resonant Kerr nonlinearity and the cavity dispersion can lead to significant narrowing of the comb spectrum. The implementation of highlosses is shown to be favourable and finally injection locking of QCLs around the roundtrip frequency provides a stable knob to control the FM state and recover the maximum width.
The quantum cascade laser has evolved to be a compact, powerful source of coherent mid-infrared light. However, its fast gain dynamics strongly restricts the formation of ultrashort pulses. As such, the shortest pulses reported so far were limited to a few picoseconds with some hundreds of milliwatts of peak power, strongly narrowing their applicability for time-resolved and nonlinear experiments. Here, we demonstrate an approach capable of producing near-transform-limited sub-picosecond pulses with several watts of peak power. Starting from a frequency modulated phase-locked state, ultrashort pulses are generated via external pulse compression. We assess their temporal nature by means of a novel optical sampling method, coherent beatnote interferometry and interferometric autocorrelation.
A convenient light source together with a suitable detector comprise the basic setup for sensing and imaging applications.
We present a flexible terahertz (THz) frequency comb source operating at room temperature that provides great freedom in the spectral content design. A robust setup merges two mature technologies, namely optical fibre communications and opto-electronic frequency conversion (photomixing). The quality of the generated THz comb is proven by the observation of the pressure-dependent collisional broadening of an ammonia molecular absorption line. Our presented THz source is expected to enhance the sensitivity and accuracy of sensing applications in general.
The photon-driven nature of the transport in terahertz quantum cascade laser can be exploited to detect light. Responsivities higher than 16 V/W are demonstrated on a patch-array antenna coupled device. The ~ps lifetimes also allows ultrafast operation. Preliminary studies suggest bandwidth higher than 5 GHz.
We present ring-shaped THz Quantum Cascade lasers operating in four different emission regimes, including single-mode, harmonic state, dense comb, and chaotic multimode emission. The dense comb regime exhibits over 30 equidistant modes covering a bandwidth of 622 GHz. A single and narrow beat note at the roundtrip frequency is indicating comb formation. Our experimental results are explained accurately by a numerical model based on the Maxwell-Bloch formalism including the concept of the so-called linewidth enhancement factor, which describes the change of the refractive index induced by the modulations of the optical gain.
The recent discovery of AV$_3$Sb$_5$ (A=K,Rb,Cs) has uncovered an intriguing arena for exotic Fermi surface instabilities in a kagome metal, displaying charge ordered and superconducting phases with unconventional properties. In this presentation I will discuss the understanding of these instabilities that emerges from a range of – partially complementary and partially controversial – experiments and our recent theoretical studies. As a first step, we develop a theory of electronically mediated charge density wave formation. Additionally, we show that the sublattice interference mechanism is central to understand the formation of superconductivity in kagome metals. Altogether, the existing body of work establishes AV$_3$Sb$_5$ as platform for correlated quantum phases of great promise.
The Kitaev model on the honeycomb lattice is a paradigmatic system known to host a wealth of nontrivial topological phases and Majorana edge modes. In the static case, the Majorana edge modes are nondispersive. When the system is periodically driven in time, such edge modes can disperse and become chiral. We obtain the full phase diagram of the driven model as a function of the coupling and the driving period. We characterize the quantum criticality of the different topological phase transitions in both the static and driven model via the notions of Majorana-Wannier state correlation functions and momentum-dependent fidelity susceptibilities.
The relation between the pseudogap phase and the superconducting dome in high Tc superconductors is still not well understood despite intense research. To develop better insight into this relation and understand the electronic properties of these materials, we study the Fermi surface via time- and angle-resolved photoemission spectroscopy (tr-ARPES). We measure the size and topology of the Fermi surface, allowing us to quantify the carrier density and the charge interactions. For Bi2212 at 22% doping, the Fermi surface shows a pump induced Lifshitz transition, accompanied by the lack of a pseudogap. For optimally doped Bi2212, we observe a Lifshitz transition (from hole-like to e- like) at high fluences of light.
Electron transfer is a crucial part of chemical reactions which drive everyday processes. With the help of an electro-chemical radiofrequency scanning tunneling microscopy setup, we are observing single electron mediated oxidation-reduction processes in transition metal corroles. We are specifically distinguishing different valence states of a transition metal ion and controllably switch from one state to another. A systematic study of such phenomena would be critical to understanding the nano-scale behavior of catalysts, molecular sensors, and batteries relevant to the development of novel material and energy applications.
The maximal vortex velocities $v^*$ are limited by the flux-flow instability (FFI) and contain information on the scattering mechanisms of charge carriers in the samples. However, the nucleation of FFI does not necessarily occur in the entire sample but can have a local character. Here, we demonstrate that the $v^*$ in superconducting MoSi films with smooth edges can exceed $v^*$ in films with rough edges by an order of magnitude. Our findings indicate that the energy relaxation times deduced from $v^*$ values should be treated with consideration of the microscopic properties and fabrication-induced features of the samples.
Extension of nanostructures into the third dimension is now a major approach in magnetism, superconductivity, and spintronics due to recent advancements in synthesis techniques and discovery of rich novel phenomenology induced by geometry, curvature, and topology effects. Herein, certain shape and curvature induced effects in ferromagnetic 3D nanostructures are presented, with focus on Co-Fe nanovolcanos and magnonic conduits fabricated by focused electron beam-induced deposition and characterised by microwave spectroscopy in conjunction with micromagnetic simulations. The broad tunability of magnon frequency spectra in direct-write Co-Fe nanostructures makes them good candidates as prospective platforms for 3D nanomagnonics and inverse-design magnonic devices.
High-performance and sustainable technologies call for novel light-weight high-temperature structural materials as gamma-TiAl-based alloys, which – in terms of weight – clearly outperform classical Ni based alloys. The typical research focus lies on their mechanical properties. However, in order to correctly interpret electrical materials testing techniques also their electrical behavior is important. Here, local-probe techniques, like conductive atomic force microscopy (CAFM) and micro four-point probe (µ4PP) measurements, were used to determine the specific resistivity of the constituent phases of a technical Ti-43.5Al-4Nb-1Mo-0.1B (at%) gamma-TiAl based alloy. The different phases exhibit noticeably different resistivity values varying over two orders of magnitude.
Changes in the ordering and electric metastable effects make the precise power rating of photovoltaic copper-zinc-tin-sulphide (CZTS) devices difficult. Reliable measurement routines are crucial for total yield prediction and investment return calculations. The aim was to find faster methods to stabilize CZTS solar devices using illumination and thermal treatment. The method used here on CZTS solar devices was by making four different routes combining thermal treatment in 85°C and 100°C with illumination in 25°C and 50°C. As a result, the route with two consecutive annealings at 100°C and 85°C followed by illumination at 25°C provides the best power stabilization.
The goal of our work is generating an automated workflow for calculating quasi-particle band gaps within the so-called GW method. The resulting protocol is applied to a large materials dataset of about 100 materials, from binary to quaternary compounds. Conventional approaches of performing these calculations require significant amounts of computational resources and user interaction, inhibiting efficient investigation of large datasets or high-throughput procedures. To avoid this, we employ a basis set extrapolation method for correcting errors arising due to finite energy cut-offs and show that it is possible to design practical workflows, which can be implemented in existing workflow managers easily and produce high-accuracy data while requiring minimal user interaction.
The Poster Session is held on Tue and Thu. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Tue.
Quantum-key distribution (QKD) is one of the most promising strategies for perfectly secure communication.Protocols based on entangled photon pairs are particularly attractive because of enhanced tolerance to losses and simplified generation of perfectly random secure keys. We use semiconductor-based sources of entangled photon pairs to implement QKD. Different from sources explored so far, quantum dots offer the triggered generation of near-unity entangled photon pairs and have the potential of generating photon pairs at GHz rates. We demonstrate continuous key generation for 13 hours between two buildings, connected via a 350 m single mode fiber with a resulting average error rate of 1.91% and a key rate of 135 bits/s
Quantum systems based on cold atoms trapped in tweezer arrays are powerful analog simulators of the Hamiltonians they implement. Their experimental control has advanced to a point where they can be programmed to simulate a wide variety of physical systems. We report on a circuit- and gate-based description of cold atomic quantum simulators and how they integrate into a modern quantum computing software stack such as Qiskit. This paves the way to using non-standard quantum hardware beyond qubits for quantum information processing. As an example, we investigate variational algorithms for cold-atom-based simulators.
We develop a framework (based on a recently studied framework of tensor decompositions) to decompose multivariate polynomials into univariate polynomials in a general way, explicitly expressing the polynomial's invariance. If the polynomial is contained in some positivity cone (for example sum of squares polynomials), we introduce and characterise corresponding inherently positive decompositions. We show under which assumptions an invariant decomposition exists and provide explicit constructions for all cases. We prove that inherently positive decompositions can be arbitrarily more costly than unconstrained ones. Subsequently, we show that unconstrained decompositions cannot contain any computable local certificate of positivity for globally nonnegative polynomials by formulating an undecidable problem in this context.
While a lot of effort has been made to understand the physical cause and effect relations, a general characterization of the ones that are, at least in principle, admissible by a logically consistent theory is still missing. With this poster I present the main ideas and formalisms that are used in this research direction, focusing both on the quantum and the classical case. The presentation is especially focusing on the cyclic causal structures, which are of the most interest due to the corresponding interpretation as "time traveling" scenarios and the possible physical understanding through the theory of general relativity.
Transmon qubits require a large shunt capacitance to decrease the sensitivity to charge fluctuations. It is usually realized by very large capacitor plates, which increase the coherence due to decreased coupling to parasitic losses localized in material interfaces but it lowers the achievable integration density and increases parasitic cross coupling. We achieve the large capacitance by narrow (≥100nm) vacuum gaps micro-machined on suspended silicon membranes. The finger capacitor has 99.6% of the electric field energy stored in vacuum and effective permittivity close to unity. The result is a compact on-chip transmon qubit with state of the art coherence per footprint area and losses limited by metal surface impurities.
Multipartite entanglement can be quantified by considering Local Operations assisted by Classical Communication (LOCC). However, for systems with fixed local dimensions, the partial order induced by LOCC is generically trivial. Consequently, we study a physically motivated extension of LOCC: multi-state LOCC. Here, one considers simultaneous LOCC transformations of finitely many pure states. In the multipartite case, we show one can change the stochastic LOCC (SLOCC) class of the individual states; that one can perform transformations not possible in the single-copy case, transferring entanglement from one state to the other; provide examples of multipartite entanglement catalysis; and find improved probabilistic protocols. In the bipartite case, we find numerous non-trivial LU transformations.
Despite their involved structure transformations via local operations assisted by classical communication (LOCC) are an active field of research due to their relevance to entanglement theory and their natural occurrence in communication scenarios.
However, generically no LOCC transformations are possible among multipartite pure states. Therefore, we focus in this work on entanglement classes containing permutation symmetric states, which are promising candidates for a richer LOCC structure and study their entanglement properties. We characterize the local symmetries of important classes and identify possible LOCC transformations, as well as states which can neither be reached via finite-round LOCC protocols nor converted to some other pure state within a single round of LOCC.
Permutation-symmetric states are both mathematically interesting and physically relevant. To understand these states better, it is important to study their entanglement properties and the allowed transformations via local operations assisted by classical communication (LOCC) which are the free operators in the resource theory of entanglement. We characterize the stabilizers of a large class of pure multipartite permutation-symmetric states and study state transformations restricted to finite-round LOCC within stochastic LOCC (SLOCC) classes that contain these states. In this poster, we focus only on 3- and 4-qutrit permutation-symmetric pure states and present their local symmetries and interesting LOCC transformations in details.
We consider graph states under party-local Clifford transformations (PLC). Such transformations arise e.g. in quantum networks where shared entanglement between spatially close nodes complements local operations. Bravyi et al solved PLC equivalence of graph states for 3 parties via the introduction of an entanglement generating set (EGS), a finite set of states into a collection of which every graph state decomposes uniquely under PLC. We show that EGS is infinite for $\ge 3$ parties and that finding states in the EGS is equivalent to the classification of tuples of alternating matrices. Moreover, we generalize the notion of local complementation, which describes the action of local Clifford transformations on graph states.
In quantum computation, indefinite causal structures allow to perform certain tasks more efficiently than any conventional (causal) quantum algorithm. For example, the quantum switch can decide whether two unitary gates commute or anticommute with a single call to each gate, while in any causal quantum algorithm at least one gate has to be called twice. A generalization of this task to $n$ unitary gates, can be solved with the quantum-$n$-switch and a single call to each gate, while it was expected that the best causal algorithm calls $O(n^2)$ gates. We present more efficient causal algorithms for this task and conclude that this advantage is smaller than expected so far.
Characterizing and controlling the coupling between qubits and environmental degrees of freedom is one of the central problems in quantum systems engineering. The coupling of one quantum system to multiple environmental degrees of freedom attracted significant attention during the last years both on theoretical and experimental sides, especially in the field of superconducting quantum circuits. In this work we investigate the problem in the context of 3D waveguide Quantum Electrodynamics (wQED), and demonstrate that in a typical experimental situation the environment can be considered as consisting of a global and a local bath. We realize an experimental protocol to extract the respective temperatures of the two baths.
We develop an optical technique to perform the quantum state tomography of a dipolar scatterer’s state of motion. We approach this problem by experimenting with trapped ions and trapped silica nanoparticle as levitated dipolar scatterers. By manipulating the light emitted by the scatterers, we aim to measure the position and the variance operators of the scatterer’s state of motion. This will allow us to identify quantum states of motion such as superposition of Fock states, squeezed states or cat states, in a full-optical manner.
Trapped ions are a well-established platform for analog or variational quantum simulation of quantum magnetism. Up to now, ions in linear Paul traps allow for simulations of the 1D Ising model with up to 50 spins. In our project, we aim for extending this approach to the second dimension which will enable studies of 2D non-equilibrium physics with a larger particle number (> 50). Here we present the first results from our new ion trap apparatus whose centerpiece is a novel monolithic micro-fabricated linear Paul trap, enabling us to create the anisotropic potentials required for trapping 2D ion crystals with simultaneous optical access for imaging and single-ion addressing.
The Poster Session is held on Tue and Thu. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Tue.
Es werden die ersten Highlights des FFG Projekts der FTI-Initiative “Produktion der Zukunft” präsentiert. Das Ziel ist, eine konventionelle, erdölbasierte Wickelfolie für Supermarkt-Palettenverpackungen durch eine biobasierte, recycelbare Stretchfolie zu ersetzen. Da biobasierte Kunststoffe meist teurer, steifer und weniger dehnbar sind, sollen funktionale Perforationsmuster entwickelt werden, welche dabei helfen, Material einzusparen. Mit dem biomimetischen Lösungsansatz werden Bienenwaben-, Falt- und auxetische Strukturen als Vorlage für Perforationsmuster herangezogen. Um Materialverschwendung bei mechanischen Zugversuchen zu minimieren, werden FE Simulationen durchgeführt und ein iterativer SKO Algorithmus soll erstellt werden, welcher optimale Perforationsmuster berechnet. Das Ergebnis soll eine biobasierte, recycelbare Stretchfolie mit einem funktionalen und materialsparenden Perforationsmuster sein, welche ihre weniger nachhaltigen, erdölbasierten Vorgänger ersetzen kann.
The need for 3D integration in semiconductor industry has driven the key technology of wafer bonding to a new level. Low temperature plasma activated wafer bonding (LT-PAWB) requires high adhesive forces between two polished surfaces at reduced annealing temperatures. In this process silicon wafers with a deposited dielectric layer (SiO2, SiCxNy) are activated, contacted and annealed. The plasma condition as well as the dielectric’s composition have a significant impact on the final bonding properties. TEM-EDX, AR-XPS, AES and SE are applied on single activated surfaces and bonded samples in order to derive a model of the physical mechanisms occurring during the bonding process.
The controlled motion of single molecules gives deeper understanding of the relation between molecular motion and the chemical and geometrical properties of molecules on the surface. However, the thermal motion of molecules is a stochastic process, which is difficult to control. Here, we have used scanning tunneling microscopy, kept at temperatures of about 7 K and ultrahigh vacuum conditions, to move individual molecules controllably across a flat Ag(111) surface. Lateral manipulation is used to gain insight into the dependence of molecular dynamics on the precise chemical structure of the molecules. Moreover, vertical manipulation provides information about the dependence of molecular motion on conformational changes.
Hybrid material systems combining semiconductors and magnetic nanostructures are prospective building-blocks for the next generation of high-density recording media. In phase-separated (Ga$\delta$FeN) layers grown epitaxially on Al$_{x}$Ga$_{1-x}$N buffers, the specific concentration of Al determines the density of strain-related dislocations, which allow controlling the preferential formation of either $\varepsilon$-Fe$_{3}$N or $\gamma$’-Ga$_{y}$Fe$_{4-y}$N nanocrystals.
In this work, the influence of an AlN stopping barrier on the structural properties of Ga$\delta$FeN / Al$_{0.1}$Ga$_{0.9}$N heterostructures is systematically studied via transmission electron microscopy. Through the addition of the AlN stopping barrier, the strain-related dislocations in the buffer layer can be adjusted to stabilise the specific nanocrystal phases that determine the magnetic properties of the system.
The desire to combine properties such as ready availability, low price and biodegradability makes cellulose and its derivatives an ideal prerequisite for different applications. We demonstrate a new approach of patterning thin films based on Trimethylsilyl-cellulose (TMSC) via proximity X-ray lithography, creating positive and negative tone structures in one single exposure at the same energy dose. Of particular interest is the use of Isopropyl alcohol or water as solvent to create positive tone structures. In contrast, the negative tone was prepared with toluene. The findings suggest TMSC as a potential dual-tone photoresist applied in microelectronics or surface chemistry, used as a dielectric layer, in microfluidics or functionalized for bioassays.
Solid-oxide fuel cell (SOFC) cathode materials like lanthanum–strontium manganite (La$_{0.8}$Sr$_{0.2}$MnO$_{3}$, LSMO) are an active field of study for efficient chemical energy conversion into clean electricity. Since the surfaces play a crucial role in the relevant reactions, closer investigation is needed for establishing a model. We use our setup for pulsed laser deposition (PLD) and surface science techniques to grow and analyze single-crystalline LSMO(110) and LSMO(001) films on suitable substrates. The material analysis is facilitated by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED) and x-ray photoelectron spectroscopy (XPS) as well as density-functional theory (DFT).
Little is known about the surface tension of pure liquids in contact with their pure gaseous phases, i.e. without the presence of other gases or contaminants. This is surprising given that contaminants are known to greatly affect surface tensions values.
Recently we have developed a method to dose liquid water with UHV purity using a small cryostat[1]. We combine this approach with the pendant drop method to measure the surface tension of ultra-clean liquids. A pendant drop of the liquid is formed in UHV and carefully photographed allowing the surface tension of the ultra-pure liquid to be directly determined.
[1] Jan Balajka, et. al., Review of Scientific Instruments 89, (2018)
Collecting quantitative low-energy electron diffraction [LEED I(V)] data normally requires expensive acquisition systems that complement LEED control electronics. We design a fully functional setup, based on an Arduino controller, combining easily and cheaply available parts as part of the “Vienna Package for TensErLEED” (ViPErLEED). In addition to standard LEED I(V) signals, the design is expandable to suit the user needs. We add to the hardware design a customizable, open-source control software, which requires minimal user input. Using our own system, we collect data on well-studied, single-crystalline metal and oxide surfaces to verify the functionality and test the accuracy of the setup.
Redox chemistry on perovskite surfaces attracts attention due to these materials’ promising catalytic properties and the presence of ferroelectricity in many perovskites. In this study, STM and XPS have been used for investigating the interaction of cobalt with the $KTaO_3(001)$ surface. In UHV conditions, the freshly cleaved $KTaO_3$ surface was exposed to water vapor prior to cobalt deposition for intrinsic surface polarity compensation and to create a uniform (2x1) reconstruction. Interaction of cobalt with such surfaces was studied under oxidizing and reducing conditions and as a function of the temperature. The stability of the cobalt in its metallic, oxide, and hydroxide phases was studied and the cluster size was evaluated.
A new In Situ Spectroscopy beamline (X07DB) has been recently established at the Swiss Light Source (SLS). The beamline is now open to the user community via proposal access, offering studies of solid-gas and solid-liquid interfaces using ambient-pressure X-ray photoelectron spectroscopy. Two experimental endstations are available, capable of studying "real" catalysts such as polycrystalline/powder samples under catalytically relevant conditions, as well as model systems represented by well-defined single crystals prepared under UHV conditions. The unique capability of the beamline is the ability to perform electrochemical studies. Besides our current experimental capabilities, I will present the ongoing in-house research, instrumental development, and plans towards the scheduled upgrade of the SLS 2.0.
Perovskite surfaces are often probed by diffraction techniques, and a commonly measured (1x1) pattern is interpreted as a (1x1) atomic arrangement. We use the KTaO3(001) to demonstrate the pitfalls of this assumption. Cleaving KTaO3(001) in vacuum and a subsequent exposure to water vapour results in the formation of a (2x1) reconstruction. The (2x1) pattern is only observed in LEED at very low beam energies and low currents, then it turns into (1x1). We investigate the beam damage caused to the surface in dependence on the incident beam energy and current. The defects are identified by combined STM and nc-AFM.
We demonstrate an approach to manufacture 2D materials into nanoribbon networks. Small organic molecules deposited on 2D materials can form nanoneedles aligning predominantly in either zig-zag or armchair orientation. This study shows their usage as masks. These hybrid heterostructures are plasma etched resulting in single-crystal nanoribbon networks. Raman spectroscopy, atomic force microscopy and electrical measurements are employed to verify the ribbons’ network and transport properties. Ribbon based devices were found to exhibit pronounced gate dependent polarity switching, mimicking behaviour of ferroelectric based devices. Our method opens a new avenue for straightforward production of 2D material nanoribbon network devices with variable polarity on a scale relevant to optoelectronic applications and sensors.
The accelerator science has long sought to increase the quality factor of SRF cavities. The approach is to use Nb$_3$Sn in a thin film form grown on Cu. One main advantage of Nb$_3$Sn is its high critical temperature- twice the currently used Nb. The challenge of growing Nb$_3$Sn directly on Cu is multiple and requires the use of a barrier layer in between Nb$_3$Sn and Cu. This work hence propose Ta as the barrier layer, which was fully investigated prior to the Nb$_3$Sn sputter deposition. The results will show that Ta is indeed preventing for any Cu inter diffusion, hence allowing a optimal growth of the Nb$_3$Sn on top.
Epitaxial Ge0.9Sn0.1 layers are well-suited for Si-integrated optoelectronics. However, their thermal stability at the nanoscale is far from a complete understanding. For detailed insights into the decomposition process induced by the components' negligible miscibility and the low Sn melting temperature, in situ TEM experiments have been performed. To trace the sample evolution upon annealing, cross-sectional and plan view lamellas were cut from mechanically wedge-polished specimens and installed on MEMS-based heating chips with an in-house FIB-assisted approach. Heating experiments were carried out from 300 K to above the Sn melting point. Combining complementary TEM techniques and spectroscopy has provided valuable information for efficient synthesis and application of desired materials.
I will give an overview of the state of the art of quantum random number generation (QRNG) and quantum key distribution (QKD) and I will present recent developments to improve the performance of these technologies. So-called self-testing QRNGs allow to certify the generated entropy in real time, which is a real benefit, knowing that a statistical analysis of the random bit string is unsatisfactory. On the QKD side, efforts are made to improve the reach and key rates on the one hand, and to reduce the cost and size with photonic integrates circuits. Another challenge is the integration of the QKD systems in a telecom environment and to share optical fibres for classical and quantum communication.
As agreed at the COP 21 2015 in Paris the countries of the world promised to take immediate measures to keep the worldwide temperature rise below 2°C and therefore prevent further climate change consequences. The transformation of the energy system and utilities as its main actor are critical in this endeavor. Utilities not only drive the change to a renewable energy generation but also enable people to actively participate in this process by offering climate friendly customer solutions. Thus, turning ‘preventing climate change’ into a society-wide undertaking.
Symmetry and symmetry breaking play essential roles in a wide range of physical phenomena and have numerous applications, ranging from labelling energy eigenstates of atoms and molecules to effectively describing quantum phase transitions and topological classification of quantum matter. An intriguing example is the discovery of materials with crystallographically forbidden rotational symmetries known as "quasicrystals" which has changed the notion of the ordering in materials. Here in this talk, first I will show how a discrete quasicrystalline symmetry can emerge in an ultracold-atom-cavity quantum electrodynamics (QED) setup. Then I will discuss general conditions which guarantee the existence of continuous Lie symmetries in generic quantum-gas-cavity-QED systems, thus rendering a symmetry classification scheme for matter-field interaction Hamiltonians.
Free electron lasers (FEL) are tuneable powerful lasers ranging from the infrared to the X-ray, serving for the exploration of matter. They use a simple and elegant gain medium, where coherent radiation is generated using free electrons in a periodic permanent magnetic field generated by a so-called undulator. The light–electron interaction in the undulator leads to a bunching process, setting in phase the electron emitters. Starting from the FEL origins, first FEL oscillators results and user applications to the advent of unique intense tuneable X-ray linear accelerator FEL, the progress of the field will be reported. New directions open by the laser plasma acceleration will be discussed.
We developed a spectroscopy method for quantum sensing based on sequential weak measurements to detect the free-induction decay (FID) signal of a single carbon-13 nuclear spin. We showed that such measurements mitigate the unwanted quantum back-action, and provide a number of further advantages, including a large frequency bandwidth and possibility of efficient Fourier Nuclear Magnetic Resonance (NMR) methods. We further extended our strategy to image large nuclear spin clusters with three-dimensional atomic resolution. We demonstrated the detection of up to 29 carbon-13 nuclear spins in diamond, and showed how, by applying information-criteria principles to the detected signals, the three-dimensional atomic positions of nuclei in a diamond lattice can be recovered.
The Coupled Dark State Magnetometer is a scalar magnetometer based on coherent population trapping within the 87Rb D1 line, which is especially designed for scientific space missions. It is developed in a cooperation between the Institute of Experimental Physics of Graz University of Technology and the Space Research Institute of the Austrian Academy of Sciences.
The magnetometer is on board ESA’s upcoming JUICE mission and is going to investigate the magnetosphere of Jupiter and its icy moons.
The presentation explains the magnetometer’s working principle, its performance and the residual deviation of the magnetic field strength reading (the heading characteristics) induced by the light shift (AC Stark) effect.
We discuss quantum variational optimization of Ramsey interferometry with ensembles of N-entangled atoms, and its application to atomic clocks based on a Bayesian approach to phase estimation. We identify best input states and generalized measurements within in form of entangling and decoding quantum circuits. These circuits are built from basic quantum operations available for the particular platform. Optimization is defined relative to the Bayesian mean square error, ie we optimize for a finite dynamic range of the interferometer or the long-term instability of a clock. Remarkably, even low-depth quantum circuits yield excellent results that closely approach the fundamental quantum limits for optimal Ramsey interferometry and atomic clocks.
Frequency dissemination in phase-stabilized optical fiber networks for metrological frequency comparisons and precision measurements are promising candidates to overcome the limitations imposed by satellite techniques. However, network constraints restrict the availability of dedicated channels in the commonly-used C-band. Here, we demonstrate the dissemination of an SI-traceable ultrastable optical frequency in the L-band over a 456 km fiber network. We characterize the optical phase noise and evaluate a link instability of $4.7\cdot 10^{-16}$ at 1 s and $3.8\cdot 10^{-19}$ at 2000 s integration time, and a link accuracy of $2\cdot 10^{-18}$. We demonstrate the application of the disseminated frequency by establishing the SI-traceability of a laser in a remote laboratory.
We present a study of the Rydberg spectrum in $^{166}$Er for series connected to the $4f^{12}(^3H_6)6s$, $J_c=13/2$ and $J_c=11/2$ ionic core states using an all-optical detection based on electromagnetically induced transparency in an atomic beam. Identifing approximately 550 states, we find good agreement with a multi-channel quantum defect theory (MQDT) which allows assignment of most states to ns or nd Rydberg series. We provide an improved accuracy for the lowest two ionization thresholds to $E_{IP,Jc=13/2}=49260.750(1) cm^{−1}$ and $E_{IP,Jc=11/2}=49701.184(1) cm^{−1}$ and the corresponding quantum defects for all observed series. Our results open the way for future applications of Rydberg states for quantum simulation using erbium and exploiting its special open-shell structure.
Ultra-narrow atomic transitions have been extensively used for high-precision measurements and for the manipulation of quantum systems.
Here, we report on the observation of a narrow inner-shell orbital transition of erbium at 1299.21nm, and, for the first time, on coherent control of the atomic state with this optical transition. High-resolution spectroscopy is performed on five erbium isotopes and we determine the natural linewidth of the transition, which reaches a sub-Hertz level of 0.9(1)Hz, by coherently populating the atoms on the excited state and monitoring the decay rate. The atomic polarizability of the excited state relative to the ground state is measured and a near magic wavelength condition is realized.
Positronium is an excellent system to test bound state QED theory to very high precision, since it is almost exlusively governed by the electro-magnetic force and does not exhibit finite size effects. Numerous precise experiments have therefore been conducted in the past to measure the fine and hyperfine splitting. However, some experiments show disagreements of up to 4.5σ with most recent calculations. Furthermore, a new precision measurement of the 1S-2S transition would allow for a stringent test of QED theory in the ppb range. This talk will report on the current status of efforts at ETH Zurich to measure the 1S-2S and excited state fine and hyperfine splitting in Positronium.
We are building a cryogenic hydrogen (H) beam and pulsed ultraviolet laser detection system for the first demonstration of Quantum Gravitational States (QGS) of atoms. The enhanced statistics available through use of hydrogen atoms versus ultracold neutrons will increase sensitivity to short-range forces predicted in extensions of the Standard Model that would alter these states. Additionally, measuring hydrogen QGS will serve as a benchmark demonstration for measuring gravitational properties of anti-H, and trapping of H or anti-H using QGS methods. This talk will detail progress on building and characterizing the velocity distribution of our cryogenic hydrogen beam.
We report on measurements of the anisotropic dynamical polarizability of Dy on both sides of the 626-nm intercombination line, employing modulation spectroscopy in a one-dimensional optical lattice. To eliminate large systematic uncertainties, we use K as a reference species with accurately known polarizability. Our derived natural linewidth is in excellent agreement with literature values, which shows the accuracy of our method. In addition we demonstrate optical dipole trapping on the intercombination line, confirming the expected long lifetimes and low heating rates. This provides an additional tool to tailor optical potentials for Dy atoms and for the species-specific manipulation of atoms in the Dy-K mixture.
Charge order (CO) is established in most known hole underdoped cuprates and considered as universal property on equal footing with the pseudogap phase and superconductivity. In La-based cuprates, several studies on the charge and spin order have recently lead to controversial results in the overdoped regime. To address open questions on the origin of CO, its connection to the tentative pseudogap critical point and the spin order, we performed a thorough resonant inelastic x-ray scattering study in La2-xSrxCuO4 and La1.8-xEu0.2SrxCuO4 with dopings up to x=0.25. The results provide a comprehensive overview of the CO in La-based cuprates and elucidate the doping evolution of the incommensurability, correlation length and temperature dependence.
Multilayered cuprates possess not only the highest superconducting temperature transition but also offer a unique platform to study the interplay between competing and intertwined orders with superconductivity. Here, we study the underdoped trilayer cuprate HgBa2Ca2Cu3O8 and we report the first quantum oscillation measurements in magnetic field up to 88 T. A careful analysis of the spectra of QOs is interpreted in term of coexistence of antiferromagnetic order in the inner plane, leading to small hole pockets and charge order in the outer planes, leading to small electron pocket. The additional frequency corresponding to magnetic breakdown tunneling between the inner and outer planes is also observed.
A major difficulty in understanding cuprate superconductors is the presence of strong correlations which give rise to the rich phase diagrams of these systems. I will discuss the charge density wave (CDW) order, which was demonstrated to be intrinsic to cuprates. This modulation is observed in the intermediate carrier concentration range, below the optimal doping. While resonant X-ray scattering allowed us to establish the doping-temperature range of the static CDW order in HgBa$_2$CuO$_{4+\delta}$, resonant inelastic X-ray scattering enabled the discovery of the short-range CDW fluctuations at temperatures exceeding the onset of the static correlations. Such coexistence of static and dynamic CDW correlations is consistent with theoretical predictions
Cuprates superconductors undergo various charge states as electron or hole carries doping into the parent charge-transfer insulators. The characters of charge dynamics are thus of great importance to understand the underlying physics behind the complex phase diagram. Using O K-edge resonate inelastic X-ray scattering, we studied the low-energy charge excitations in hole-doped superconducting Bi2Sr2CaCu2O8+x and their evolution with doping in three representative doping levels. A steep dispersive excitation is unveiled, which much resembles the acoustic plasmon observed in electron-doped cuprates. While the dispersion gets only slightly steeper as doping increases, its intensity increases considerably. Our results confirm the presence of the acoustic plasmon excitation in the double-layered Bi2Sr2CaCu2O8+x.
Exploring strongly interacting engineered vortex patterns in copper-oxide superconductors requires vortex distances smaller than the London penetration depth. With the focused beam of a helium ion microscope, we fabricate pinning sites with spacings down to 40 nm in YBa2Cu3O7−𝛿 thin films and investigate vortex commensurability effects at unprecedented high magnetic fields at the order of 1 T. In quasi-kagomé tilings, magnetic caging of vortices is observed and confirmed by molecular dynamic simulations of vortex motion. These findings open the path for the realization of even more complex structures and intriguing possibilities for the manipulation of vortices in high-temperature superconductors.
Understanding of the ordering tendencies exhibited by the cuprates can give valuable insight into the origin of superconductivity in these complex oxides. Thus, I will present the study of the charge density wave (CDW) order and discuss its connection with the electron-phonon coupling in Nd$_{2-x}$Ce$_x$CuO$_4$. Recent studies suggested that the CDW order can cause an anomalous softening of the longitudinal Cu-O bond-stretching phonon mode around the order’s wave vector, $q_{CDW}$. Motivated by these results, we performed temperature and doping-dependent inelastic X-ray scattering studies combined with the DFT calculations for the parent compound.
The normal state of cuprate high-temperature superconductors exhibits a plethora of unusual behaviors that hinder the understanding of the superconducting phenomenon. Despite this complexity, the behavior of the scattering rate was demonstrated to be surprisingly simple. It is doping and compound independent and exhibits a quadratic temperature dependence, like a Fermi liquid. A distinct property of Fermi-liquids is that they obey Kohler’s rule, $\delta\rho/\rho_0=F\left(H\tau\right)$, which is a scaling relation between the magnetoresistance $\delta\rho/\rho_0$, magnetic field $H$, and lifetime $\tau$. We will demonstrate that this scaling is obeyed throughout the phase diagram of cuprates and further illustrate the universality of the scattering rate, and verify the Fermi-liquid nature of itinerant carriers.
Cuprates are prototypical for high-temperature superconductivity and host a vast family of com-
pounds. Recently, the new Ba$_2$CuO$_{3+y}$ cuprate superconductor has been discovered, which challenges the previous physics picture in other cuprate superconductors by (1) exhibiting superconducting only in a narrow ’highly overdoped’ doping region ($y$=0.2) (2) hosting a different Fermi-surface; To shed light onto this most unusual cuprate we use density-functional-theory (DFT) combined with dynamical-mean-field-theory (DMFT) and reveal that correlation effects drive a charge-transfer between CuO$_{1.5}$ and CuO planes in Ba$_2$CuO$_{3.2}$, which leads to a quasi 1D $d_{y^2-z^2}$ band, instead of the common 2D $d_{x^2-y^2}$. This discovery offers a new theoretical explanation to understand the recently discovered superconductor Ba$_2$CuO$_{3.2}$.
The idea that unconventional superconductivity (SC) in Sr2RuO4 is a solid-state analogue to superfluid 3He-A has been recently overturned. Here we use 17O NMR spectroscopy to probe the SC state in Sr2RuO4 in the limit T→0 down to B/Bc2< 0.2. While the NMR Knight shift K includes contributions of both field-induced quasiparticles (QP) and a possible spin polarization of the condensate, the specific heat C/T includes only the QP term. By comparing the field dependences of K and C/T, we establish an upper bound for the condensate response of < 10% of the normal-state susceptibility, which is sufficient to exclude odd-parity candidates [1].
[1] Proc. Natl. Acad. Sci. (2021); arXiv:2007.13730
Exploration of novel materials in search for unconventional superconductivity can lead not only to the synthesis of compounds with important technological applications but also contributes to understanding the mechanism of this phenomenon. One such compound is murunskite (K2FeCu3S4), a material isostructural to iron-based superconductors. I will discuss our synthesis efforts and characterization of this material through measurements of the structural, electronic and magnetic properties. Our study indicates that murunskite is a Mott insulator with sulfur orbitals partially open and electronically active, similar to oxygen orbitals in cuprates. Furthermore, the conduction band is cuprate-like while the valence band is pnictide-like, positioning murunskite as an interpolation compound.
In quantum field theory, states with large quantum numbers under the conserved charges of the theory are generically amenable to a semiclassical description. This observation underlies some recent progress in the study of the spectrum of operators with large internal charge in strongly coupled conformal field theories. I will review these results and show how similar ideas can be used to overcome the breakdown of perturbation theory for multi-legged amplitudes in the epsilon expansion.
Glueballs, bound states of gluons, can be studied by mapping certain limits of strongly coupled gauge theories to higher-dimensional theories of weakly coupled gravity. This approach has the advantage of permitting computations of glueball decay rates for processes involving mesons as final states. I will give an overview of the calculation of glueball decay patterns in the Witten-Sakai-Sugimoto model, which describes a gauge theory similar to QCD, and a brief comparison of results with experimental data.
The process of hadron formation via the strong force is not yet fully understood. Quarkonia, bound states of a heavy quark and its anti-quark are ideal probes to study this process. Theoretically the production of quarkonia can be described by the Non-Relativistic Quantum Chromodynamics (NRQCD) framework. The factorization approach that is employed by the framework relies on experimental inputs like quarkonium production cross sections and polarization measurements. The LHC experiments have published a multitude of quarkonium cross section and polarization measurements. However, these measurements mainly cover the S-wave states and measurements for the P-wave states remain scarce. We present the first measurement of P-wave state polarization, namely the polarization of the prompt χ_c1 and χ_c2 mesons, using data that has been collected in 2012 by the CMS experiment at the LHC in proton-proton collisions at √s = 8 TeV. We find that the two states have significantly different polarizations, in agreement with NRQCD predictions. We also briefly discuss global fit efforts that make use of these new measurements.
The goal of this analysis is to make a precise measurement of the magnitude of the element |$V_{cb}$| of the Cabibbo–Kobayashi–Maskawa matrix based on B-decays to the exclusive final state $D^{*-} l^+ \nu_l$. We will explain how this new measurement addresses several limitations of previous determinations and will help to clarify the experimental status of |$V_{cb}$|. The first steps are to measure the branching fraction and kinematic variables of the decay -- preliminary results will be presented. This analysis is based on the data recorded by the Belle II experiment at the SuperKEKB collider.
A long-standing discrepancy in flavour physics is observed in the determination of the CKM elements |Vcb| and |Vub|. For |Vcb|, a combined tension of about 3σ is seen between different methods of determination. We revisit the decay B- -> D0 l- nu_l using data of the Belle II experiment to clarify the experimental status of this parameter. In addition to a measurement of the decay branching fraction and a test of lepton universality between electron and muon channels, the rate as a function of the 4-momentum squared of the lepton-neutrino q^2 is determined to fit for the CKM element |Vcb|. The preliminary results will be presented.
A new theoretical framework based on the Operator Product Expansion allows to extract the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element Vcb with O(1/mb^4) precision. This approach requires also the measurement of the moments of the q^2 distribution, the sum of the charged lepton and neutrino 4-momenta squared, which are unmeasured up to now. The |Vcb| parameter will be determined from the branching fraction of the reconstructed B-meson decay into a hadronic system with charm, a light lepton and the associated neutrino, combined with measurements of q^2 moments of the lepton-neutrino system. In this talk preliminary results, based on the data sample collected by the Belle II experiment, will be presented.
We present the measurement of Higgs boson production in association with a W/Z boson considering only events where the Higgs boson decays into a bottom quark-antiquark pair. The talk focuses on the analysis of 41.5/fb collision data taken by the CMS experiment in 2017 at a center of mass energy of 13 TeV. The talk aims at summarizing the analysis methods as well as presenting potential areas of improvement with regard to the full Run II result. Additionally, analysis results are put into context of the discovery of the Higgs boson decay into a bottom-antibottom pair.
We have developed two quantum classifier models for the $t\bar{t}H(b\bar{b})$ classification problem, both of which fall into the category of hybrid quantum-classical algorithms for Noisy Intermediate Scale Quantum devices. Our results serve as a proof of concept that Quantum Machine Learning (QML) methods can have similar or better performance, in cases of low number of training samples, with respect to conventional methods. To utilise algorithms with a low number of qubits we investigated different feature reduction methods. We addressed different configurations of two models, representative of the two main approaches to supervised QML today: a Quantum Support Vector Machine, a kernel-based method, and a Variational Quantum Circuit, a variational approach.
Goto Room B for the CHIPP and V.-F- Hess award talks
Two open questions in physics are the nature of dark matter and the fundamental nature of neutrinos. DARWIN is a next-generation experiment aiming to reach a dark matter sensitivity limited by the cosmic neutrino background. The core of the detector will be a TPC with 40 t of liquid xenon as dark matter target. The large xenon mass, the ultra-low radioactive background and the low energy threshold will allow for a diversification of the physics programme beyond the search for dark matter particles: DARWIN will be a true low-background, low-threshold astroparticle physics observatory. I will present the status of the project, its science reach, and discuss the main R&D topics.
The Astroparticle Physics Group at the University of Zurich operates a high-purity germanium (HPGe) spectrometer (Gator) in a low-background environment underground at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy. The 2.2 kg $\gamma$-ray spectrometer is one of the world’s most sensitive HPGe detectors with an integrated count rate of (86.2 $\pm$ 0.7) events/(day kg) in the energy region 100-2700 keV. It is used to screen and select materials for rare-event search experiments such as XENON, DARWIN, GERDA and LEGEND. We describe the general facility, the recent upgrades and their impact on the background level. We also demonstrate its sensitivity by presenting the results for several material samples.
Gamma-ray bursts have been studied for over 50 years; primarily through their spectral and temporal profiles. However, their physics is sometimes impossible to answer without the addition of polarization information. From recent instrument observations, it was understood that in combination with a long mission, detailed temporal and energy resolved analyses are necessary to further constrain theoretical models.
POLAR-2, manifested for launch in 2024, includes a polarimeter and spectrometer and aims to address these bottlenecks such that 50 GRBs are measured with equal or better quality compared to the best seen by its predecessor; POLAR. Its respective design, anticipated scientific performance and first results of a polarimeter module will be discussed.
In the Standard Model (SM) of particle physics the conservation of baryon number (B) is an empirically observed symmetry. However, B could be an approximate symmetry of Nature, and violated by small amounts as predicted by many SM extensions. Using XENON1T/nT data we can search for inclusive radiogenic nucleon decays: model-independent $N\rightarrow X + \textit{anything}$ channels, also called \textit{invisible decays}, that are feebly dependent on the details of final state. Preliminary results of \textit{p}, \textit{nn}, and \textit{pp} decays of $^{129}$Xe from XENON1T data will be presented and compared with current limits.
Der Brundtland -Report „Unsere gemeinsame Zukunft“ (1987) legt nahe, dass Bildung bei der Realisierung einer gerechten, friedlichen und nachhaltigen Gesellschaft eine Schlüsselrolle zukommt. In der aktuellen Weiterentwicklung – den Sustainable Development Goals (SDG) – hat sich die Weltgemeinschaft dafür ein eigenes Ziel gesetzt, nämlich die Gewährleistung einer „inklusiven, gleichberechtigten und hochwertigen Bildung“ für alle (SDG4). Von der Bildungspolitik werden aktuell zahlreiche Initiativen zur Förderung des Unterrichts in den MINT-Fächern (Mathematik, Informatik, Naturwissenschaft & Technik) propagiert. Im Vortrag wird der Frage nachgegangen, in welchem Verhältnis diese MINT-Initiativen zu einem bildenden naturwissenschaftlichen Unterricht stehen und welchen Beitrag der Physikunterricht und die fachdidaktische Forschung zur Realisierung des SDG 4 leisten kann.
Although learning Quantum Computing traditionally requires solid basics of quantum physics and mathematical tools, several national and international initiatives are trying to find innovative ways to introduce the main concepts already at high school level.
Combining visualization, engaging interface and a fundamental creative component, we believe that using games is one of the most effective ways to teach and inspire young minds.
We investigate two approaches: creating games for explaining fundamental concepts such as entanglement, measurements and gates; and creating tools to let people make their own games by using python and Qiskit, the free software development tool used to program Quantum Computers.
The International Particle Physics Outreach Group (IPPOG) has been making concerted and systematic efforts to present and popularize particle physics across all audiences and age groups since almost 25 years. One of the main tools IPPOG, the Resource Database (RDB), is an online platform containing the collection of high-quality engaging education and outreach materials in particle physics and related sciences. After 10 years, new RDB is being developed aiming to become the world primary source of particle physics outreach and education material for teachers, educators and scientific community, and thus help to bring particle physics closer to the society and to bridge the gap between school curricula and modern physics.
Digital media can enrich physics teaching in many facets. To be able to use digital media in the classroom, physics teachers need corresponding competencies. The foundations for these competencies should be laid during studies. But which digital competencies should prospective teachers already acquire during their studies? And which of the various actors in teacher education should ideally promote which competencies? Based on the orientation framework DiKoLAN (Digital Competencies for Teaching in Science Education), a concept tailored to the PH Thurgau was developed. In this talk, the procedure for determining the necessary competences and first results from a pilot run of the associated survey instrument will be presented.
This talk presents recent experimental demonstrations that use integrated nanophotonic processors for various quantum computations such as quantum machine learning and in particular reinforcement learning, where agents interact with environments by exchanging signals via a communication channel. We show that this exchange allows boosting the learning of the agent. Another experiment underlines the feasibility of photonic quantum system for so-called probabilistic one-time programs that allow for secure classical computation tasks. As outlook I will discuss technological challenges for the scale up of photonic quantum computers, and our group’s current work for addressing some of those.
In this talk, I will discuss applications of quantum networks going beyond quantum key distribution. I will show that quantum networks can be used to perform distributed computing, both classical and quantum. Furthermore, I will present a recent experiment that shows quantum communication in a multipartite network and allows – besides security in the communication – keeping the identities of the participating parties secure. I will conclude with a discussion of experimental challenges in realizing advanced networked quantum protocols.
Optically active spins in solids are often considered prime candidates for scalable and feasible quantum-optical devices. Numerous material platforms including diamond, semiconductors, and atomically thin 2d materials are investigated, where each platform brings their own advantages along with their challenges. Semiconductor quantum dots are the current state-of-the-art for optical properties such as tuneability, brightness and indistinguishability. Their nickname "artificial atom" was coined historically to highlight how similar they can be to isolated single atoms, but in fact they are far from the realisation of a simple two-level system. The inherently mesoscopic nature of a quantum dot leads to a multitude of dynamics between spins, charges, vibrations, and light. In particular, it offers a unique realisation of a tripartite interface between light, a single proxy qubit (electron spin) and an isolated spin ensemble (nuclei). Ability to control these constituents and their mutual interactions creates opportunities to realise an optically controllable ensemble of ~50,000 spins. In this talk, I will present the two-decade journey from treating the quantum dot nuclei as noise to the observation of their collective magnon modes and eventually to their tuneable quantum correlations, all witnessed via a single electron spin driven by light.
Algorithms that run on near term quantum devices will be a decisive step towards applications of quantum computers. In this talk I will focus on optimization problems and how to encode and solve them on quantum devices. I will present the parity mapping and algorithms that make use of it. In particular, the talk will focus on encoding of optimization problems with higher-order terms and side conditions in the form of hard constraints.
In this work, we report the extension of our setup by combining a sinusoidal modulation of the magnetic field with the synchronous detection of the reflectance difference spectroscopic MOKE (RD-MOKE) signal which allows recording hysteresis loops continuously as a function of coverage, time or temperature. We illustrate the capabilities of our setup for Ni thin films grown on a Cu(110)-(2x1)O surface and the subsequent deposition of cobalt tetramethoxyphenylporphyrin (CoTMPP) thin layers. The adsorption of the molecules induces characteristic changes in the magnetic properties that are monitored as a function of the coverage and temperature, revealing the decrease of the Curie temperature upon CoTMPP deposition on Ni films with different thicknesses.
Low-Energy Electron Diffraction (LEED) is a structure-sensitive technique commonly used to determine periodicity and order of a surface phase. Quantitative analysis of the modulation of beam intensities as a function of voltage (LEED $I(V)$) also gives access to the surface atom positions. This requires complex calculations and optimization of structural parameters. The Erlangen program package TensErLEED readily performs this task, but its required user input is prohibitively complex.
We introduce the new "Vienna Package for TensErLEED" (ViPErLEED), which greatly simplifies the use of TensErLEED, only requiring a standard structure file and a handful of user parameters. The package also includes a utility for extracting experimental $I(V)$ spectra from LEED videos.
Paper is increasingly used as a packaging material in particular also in food packaging. In the latter case it is necessary to get more insight into the adsorption and desorption behavior of aroma molecules on and in the paper network. Food packaging should keep the aroma molecules inside the food and protect the food from the environment. Paper is a porous material and this can be used as an advantage. The CD-Laboratory for mass transport through paper is conducting research along this line. It will be shown that temperature programmed desorption can be used to study the interaction of organic molecules with cellulose based surfaces.
In this work we present a new method of acquiring force volume data in a single scan using mixing products of different drive tones. The acquisition of such data is generally limited by the stand-by time of the system since it can easily take more than 10 hours. We address this limitation by combining our low temperature (LT) tuning fork atomic force microscopy (AFM) with two more advanced measurement methods using multiple drive frequencies and detection of up to 32 mixing products.
From the measured 32 lock-in channels we reconstruct the interaction force between the sample and the tip, resulting in a force volume measurement acquired in a single scan.
Photoemission Tomography has been widely used to study organic molecules adsorbed on metal substrates. Traditionally, the final state was taken as a plane wave in numerical simulations. This formalism has been very successful but discrepancies are also clearly observable, e.g. in the circular dichroism and the photon-energy dependence of the photocurrent.
In this work the Lippmann-Schwinger equation is used for a more accurate description of the final state.
After presenting the theoretical formalism and technical details about its implementation into an ab-initio framework, results are presented for some prototypical small molecule systems including CO and benzene which highlight important differences compared to a plane wave final state description.
Angular-Resolved Photoelectron Spectroscopy (ARPES) can benefit greatly from theoretical simulations as the observed momentum-space signature of the electronic structure is often quite involved. With the recent developments in ultra-fast laser physics, ARPES is now being used to also investigate time-resolved phenomena, e.g. for excited-states (pump-probe experiments).
In this talk we show how real-time Time-Dependent Density Functional Theory can be used to simulate time-resolved ARPES. Accounting for dynamical processes directly is an advance over established methods and reproduces experimental findings such as circular dichroism in molecular monolayers or 2D systems. Furthermore, we present how this method can be used to directly observe excitations in the electronic structure in time.
In metals that form a bulk hydride upon hydrogen exposure, the surface properties depend on the state of the bulk. This impedes the use of surface science methods in general to post mortem analysis. We have developed a method to reversibly hydrogenate thin metal films in-situ under conditions suitable for electron spectroscopy measurements. As a proof of concept, we measure the temperature dependent pressure-composition isotherms and the electronic structure of the titanium- and vanadium hydrogen systems. The results are discussed in conjunction with recent discoveries that substoichiometric hydrides of vanadium and titanium show catalytic activity towards ammonia synthesis.
Carbon contamination is a notorious issue in surface science, especially in near-atmospheric conditions. Using APXPS we analysed the build-up of carbon on a rutile $TiO_2(110)$ single crystal when exposed to vapour and liquid water. Factors such as beam illumination, gas composition, and interaction with liquid water are shown to affect surface contamination. X-ray irradiation locally increases the amount of carbon, while environmental conditions determine the initial overall contamination level. Introducing molecular oxygen can induce surface cleaning under irradiation. Our results support the hypothesis of progressive removal of carbon from chamber walls by competitive adsorption of water molecules following repeated exposure of the vacuum chamber to water vapour.
The IRAS system GRISU ( GRazing incident Infrared absorption Spectroscopy Unit) was developed for investigations in the research field of single atom catalysis. It combines the commercially available FTIR spectrometer Bruker Vertex 80v with an UHV chamber. The optics placed in HV and UHV was optimised for high throughput. In comparison to a system using two parabolic mirrors (f=250 mm) simulations show an about 20 times higher throughput of GRISU when probing the molecular beam spot on the sample. The optical components are mounted precisely in respect to each other to ensure the high performance requirement also after long term use.
We investigate the optical dynamics of PbS nanocrystal layers on a gold thin film by microscopy-based ultrafast pump-probe spectroscopy. We probe with femtosecond resolution the transient absorption of nanocrystal films with specific thicknesses ranging from a few to 100 nm, as independently verified by atomic force microscopy. In stark contrast to individual nanocrystal and gold films, the combined system shows sub-picosecond dynamics depending on film thickness and probe wavelength. On basis of the observed parameter dependencies we discuss the models for the underlying charge dynamics in our semiconductor/metal system. While of interest for fundamental reasons, the thorough understanding of such effects is of importance for nanocrystal-based electrical and optoelectrical devices.
We present the first experimental realization of Bragg diffraction for polar and non-polar molecules [1]. Using a thick laser grating at 532 nm, we diffract a molecular beam and observe Bragg diffraction in the far-field. We study this effect for the dye molecule phthalocyanine and the antibiotic ciprofloxacin and observe a pronounced angular dependence and asymmetry in the pattern, characteristic for Bragg diffraction. We can thus realize an effective mirror and a large-momentum molecular beamsplitter with a momentum transfer of up to 18 grating photon momenta. This is an important step towards gaining control over the manipulation of functional, complex molecules.
[1] Brand et al. Phys. Rev. Lett. 125, 033604
Vienna’s Long-Baseline Universal Matter-wave Interferometer (LUMI) has successfully demonstrated interference of massive molecules consisting of up to 2000 atoms and with masses up to 28.000 amu. LUMI’s high force sensitivity of $10^{-26}$ N has also been used to sense electronic, optical, magnetic and structural properties of a very diverse class of particles. For example, measuring the diamagnetic susceptibility of barium and strontium or the polarizability of fullerenes with improved accuracy to previous measurements. Most recently we have used a magnetic gradient field to measure interferometrically the phase shifts of cesium and rubidium atoms according to their hyperfine structure.
The phenomenon of the Quantum Cheshire Cat is a paradoxical effect in which different properties of a particle seem to be spatially separated. To observe the effect, weak disturbances are applied in between the pre and postselection procedure in an interferometer setup. One may perform weak measurements and use weak values to quantify the perceived path occupations of the properties. Some light is shed on the first order behaviour of weak values. While the effect’s first demonstration was in neutron interferometry where particle and spin properties were split, in the presented experiment the energy degree of freedom is additionally separated into a third partial neutron beam.
Many of the breakthroughs in quantum science and technology rely on engineering strong Hamiltonian interactions between quantum systems. Typically, strong coupling relies on short-range forces or on placing the systems in high-quality electromagnetic resonators, which restricts the range of the coupling to short distances. We show how a loop of laser light can generate Hamiltonian coupling over a distance and report experiments using this approach to strongly couple a nanomechanical membrane oscillator and an atomic spin ensemble across one meter in a room-temperature environment. We observe spin-membrane normal mode splitting, coherent energy exchange oscillations, two-mode thermal noise squeezing, dissipative coupling with exceptional points, and sympathetic cooling of the membrane. Our experiments demonstrate the versatility and flexibility of light-mediated interactions, a powerful tool for quantum science that offers many further possiblities and is readily applicable to a variety of different systems.
Owing to its excellent isolation from thermal environment, an optically levitated silica nanoparticle in ultra-high vacuum is a strong candidate to observe quantum behavior of massive objects at room temperature, with applications ranging from sensing to testing fundamental physics. With the help of a new, non-standard cavity interaction – cavity cooling by coherent scattering – we have achieved a first step toward full quantum control of the nanoparticle motion: quantum ground state cooling. I will present our recent results on cavity interaction and discuss prospects of creating macroscopic quantum states with levitated nanoparticles.
Gravity continues to pose some of the most outstanding open problems to modern physics: it remains resistant to unification within the standard model and its underlying concepts appear to be fundamentally disconnected from quantum theory.
Thus far, testing gravity involves mainly macroscopic masses on the kg-scale and beyond. Here we show gravitational coupling between two gold spheres of 1 mm radius, entering the regime of sub-100mg sources of gravity. Our results extend the parameter space of gravity measurements to small single source masses and small gravitational field strengths. Further improvements will enable the isolation of gravity as a coupling force for objects below the Planck mass.
It is unclear how our classical world emerges from the quantum world. It is also unclear how to incorporate effects of gravity into quantum mechanics. To get experimental insights into these problems, we need to prepare larger masses in quantum states.
Magnetically-levitated superconducting microparticles make promising systems for doing this. We work with a lead microsphere of ~10^18 amu (~1ug) which we isolate from its surroundings using magnetic levitation. We read out the sphere’s COM motion using a SQUID and cool the motion by applying additional magnetic fields. We will extend our control by coupling the sphere’s motion to superconducting resonators and qubits.
This talk will be about the rich set of possibilities provided by graphene-based moiré superlattices to create and study interesting many-body physics at the intersection of strong correlations and topology. Initially driven by experimental findings in twisted bilayer graphene, related systems have been realized experimentally more recently and found to exhibit similar properties; examples are twisted double-bilayer or twisted trilayer graphene. In this presentation, I will discuss some of our recent efforts, involving a combination of analytics, numerics, and experiment, to elucidate the origin and form of correlated insulating and semi-metallic phases, flavor polarization, and superconductivity in graphene moiré systems.
Understanding nanoscale energy dissipation is nowadays among few priorities in solid state systems. Pendulum geometry Atomic Force Microscope (pAFM), oscillating like a tiny pendulum over the surface, is perfectly suited to measure minute energy loss.
Here we report on low temperature energy dissipation measurements on twisted bilayer graphene (TBG) at magic angle twist - a system with flat electronic bands and highly correlated insulating phases. pAFM showed giant dissipation peaks attributed to different electron/hole filling of the flat band. The pAFM imaging allows to map the twist angle distribution of TBG. Application of magnetic fields provoked strong quantum oscillations of the dissipation signal which is enhanced for fractional band filling.
An imminent doubt has always been around whether angle-resolved photoelectron spectroscopy (ARPES) of high-Tc superconductors, visualizing the superconducting gap in k-space, can truly represent the intrinsic bulk spectral function whose response is distorted by energy- and k-dependent matrix elements and small photoelectron escape depth. We address this fundamental question with soft-X-ray ARPES of the paradigm high-Tc cuprate Bi2Sr2CaCu2O8. The matrix elements are varied by spanning a dense k-space grid formed by the lattice superstructure, and probing depth by changing the emission angle. Invariant magnitude of the measured superconducting gap proves the relevance of ARPES for the bulk superconductivity in Bi2Sr2CaCu2O8 and calls for similar verification experiments on other high-Tc compounds.
When colloidal nanocrystals self assemble into ordered superstructures they form functional solids that inherit the electronical properties of the single nanocrystals (NCs). To what extent these properties are enhanced depends on the specific ordering of the NCs within the superstructure.
Here, the formation of supercrystals using faceted nanocrystals as building blocks was investigated by in-situ small angle x-ray scattering (SAXS) at lab and synchrotron (ELETTRA) sources. As building blocks we used magnetic FeO-nanocubes and -nanostares as well as facted semiconducting PbTe/PbS nanocrystals. Additionally, we determined the atomic crystal structure (with XRD/WAXS) of the NCs within the supercrystals and demonstrated the connection between crystal structure and superstructure via the NCs' shape.
With recent advances in quantum cascade (QC) lasers and detectors the mid-IR spectral region - often called fingerprint region, due to the characteristic fundamental absorption features of molecules in this range – becomes more and more accessible for various spectroscopic applications. Here, we present a compact liquid sensor featuring QC lasers and detectors coupled by plasmonic waveguides on a single semiconductor chip for absorption spectroscopy in the range of 1550$\,$-$\,$1650$\,$cm$^{-1}$. In a proof-of-concept experiment we show its capability of measuring the thermally induced denaturation process, i.e. the change in secondary structure, of the protein bovine serum albumin (BSA) dissolved in D$_2$O in real-time.
Recently, it has been shown that disordered dielectrics can show a photonic band gap in the presence of structural correlations, but 30 years after John's seminal proposal on the interplay between the photonic pseudo band gap in disordered photonic crystals and Anderson localization, a controlled experimental study of the transport properties in between ordered and disordered states is still lacking. In this talk, I present wave transport experiments in hyperuniform disordered arrays of cylinders with high dielectric permittivity. Using microwaves, we show that the same material can display transparency, photon diffusion, Anderson localization, or a full band gap, depending on the frequency of the electromagnetic wave.
PRL 125, 127402 (2020)
We study coupling of electromagnetic waves to magnetization dynamics. Magnon-polaritons are intensively explored in ferromagnetic materials at gigahertz frequencies. Antiferromagnets have resonance frequencies at in the terahertz band, thus, there are only a few reports of light-matter coupling in that case. We report strong magnon-photon coupling in hematite alpha-Fe2O3. A cube of hematite was placed inside a cavity that has a resonance at 0.24 THz. Our transmission data as function of temperature show very clear avoided crossing of the first cavity mode and the antiferromagnetic resonance of a cooperativity factor of 40.
M. Bialek et al, Phys. Rev. Applied 15, 044018 (2021)
Heterostructures based on AlxGa1-xN are the building blocks of state-of the-art high-power and optoelectronic devices working in the visible and ultra-violet range. It was recently found, that the self-assembly of Mn-Mgk complexes in epitaxial GaN:(Mn,Mg) and AlxGa1-xN:(Mn,Mg) allows extending the emission spectra of these In-free compounds to the (near) infrared (IR). Here, through a combination of photoluminescence excitation spectroscopy and theoretical computational analysis based on density functional theory, the most efficient emission channels are identified. Furthermore, by embedding a GaN:(Mn,Mg) active layer between AlxGa1-xN:Mn/GaN distributed Bragg reflectors or layers of porous GaN, the efficiency of the IR emission is significantly enhanced.
The MagDev project in the CHART framework develops magnet technology in support of the European Strategy for Particle Physics, in particular the international High-Field Magnet (HFM) program. The research spans fast-turnaround technology development, the research of numerical tools, innovative magnet design, manufacturing-process development, and the construction and testing of technology demonstrators for both, low-temperature and high-temperature superconducting accelerator magnets. The program shall bring innovative solutions to long-standing problems in HFMs for accelerators. In this presentation we discuss the main technological challenges, how they relate to different design approaches, our progress in experimental vwork, and the feedback that it has on the magnet design and overall R&D roadmap of CHART MagDev.
Short period undulators are the key components of future compact accelerator-based sources of X-rays. The in-vacuum and cryogenic permanent magnet technology and electromagnetic low-temperature superconducting undulators are state of the art. In this talk, we present an alternative approach based on bulk high-temperature superconductors, which combines the advantages of an electromagnetic undulator with the absence of complex winding. The design details and the first experimental results are presented. The project status is reported together with preliminary concepts for the prototype on the tomography microscopy beamline, I-TOMCAT, for the SLS 2.0 project. Finally, we discuss possible applications of this technology in FELs and undulator driven polarized positron sources for linear colliders.
The FCC-ee is one of the main candidates to succeed the High Luminosity LHC at the forefront of particle colliders. The unprecedented energy and luminosity goals in the FCC-ee require extensive simulation campaigns to validate the design. While many different codes exist that address key aspects of the FCC-ee project, it is often complicated if not impossible to combine these and merge functionalities to perform some of the simulations required for the FCC-ee.
A new collaborative project between EPFL and CERN aims to develop a modern and maintainable software simulation framework to address the key challenges of the FCC-ee. This talk presents an overview of the scope of the project as well as the first developments and results. Furthermore, future functionalities that may be addressed within this framework are presented.
The goal of the study is to reach 1% uncertainty - the most precise luminosity measurement for high pile-up pp machine. The accumulated experience and detector upgrades give a unique opportunity to improve the measurement during Run 3 and prepare for demanding HL-LHC conditions. Better luminosity precision is required to minimize its impact on numerous particle physics measurements.
The focus is put to study the beam-beam effects during the VdM and operational scans, as these effects are the main limiting factor for high luminosity. COMBI code is used for understanding them and evaluating corrections. The new optimized luminometer is assembled to provide linear measurement and stability over the operating period.
Accelerator Mass Spectrometry (AMS) is the technique of choice for the detection of environmental levels of long-lived radionuclides with typical relative abundances of 10$^{−12}$ to 10$^{−16}$. Interferences from stable isobars however used to restrict the applicability of this method to selected nuclides. The novel Ion Laser InterAction Mass Spectrometry (ILIAMS) technique at the Vienna Environmental Research Accelerator VERA overcomes this limitation by selective laser photodetachment of isobars in the ion beam. This opens up exciting possibilities in nuclear physics research ($^{90}$Sr, $^{99}$Tc, $^{135}$Cs), astrophysics ($^{182}$Hf), and geology ($^{26}$Al, $^{36}$Cl). This presentation will give an overview of the technique and its applications.
The relative formation probabilities for a range of (oxy-)fluoride molecular anions containing uranium, neptunium, plutonium, and americium during the sputtering process in a Middleton type AMS ion source from an iron oxide matrix mixed with PbF$_{2}$ have been investigated at VERA. Identifying this distribution is important for the separation of U and Np isobars via element selective photodetachment and reactive gases in the ILIAMS ion-cooler. A suitable choice of extracted molecules can suppress U in the beam by an order of magnitude compared to Np. Finally, the distribution can help identify isobaric contaminations in irradiated material produced during the development of an isotopic spike for $^{237}$Np.
The detection efficiency of Accelerator Mass Spectrometry for long lived uranium isotopes ($^{236}$U or $^{233}$U) is mainly limited by the rather low yield of the corresponding negative ions extracted from a caesium sputter ion source (≈ 10$^{–4}$). With our new sample preparation method environmental U is embedded in only 200 µg Fe$_2$O$_3$ matrix which is then mixed with PbF$_2$. Extracting U as UF$_5^–$ instead of UO$^-$ yields an improvement in detection efficiency by more than a factor 10. UF$_5^–$ extraction seems advantageous for the suppression of molecular isobaric background ($^{232}$ThH$^{3+}$, $^{235}$UH$^{3+}$) and allows operation at lower He stripper gas pressure.
The radionuclides 135Cs and 137Cs are present in the environment with an isotopic ratio 135,137Cs/Cs ranging below 10-10. The isotopic ratio 135Cs/137Cs can be used for source assessment of anthropogenic cesium input into the environment and finds applications in geology, nuclear forensics and oceanography. The combination of low concentration, low beta-decay energy and long half-life prevents the determination of 135Cs via radiometric methods with the demanded sensitivity. Therefore, we established a measurement procedure for cesium by Accelerator Mass Spectrometry at VERA. First results on isobar suppression, abundance sensitivity and 135Cs/137Cs ratios of environmental samples will be presented.
$^{90}$Sr is among the most hazardous fission products with a high production yield in the nuclear fuel cycle and is of great environmental interest due to its radiotoxicity as well as its potential as a tracer. Accelerator Mass Spectrometry (AMS) is the technique of choice for the detection of minute environmental levels of long-lived radionuclides, but the background from the abundant stable atomic isobar $^{90}$Zr has so far prevented its use for $^{90}$Sr. The novel Ion Laser InterAction Mass Spectrometry (ILIAMS) setup at the Vienna Environmental Research Accelerator (VERA) overcomes this problem by neutralizing the isobar via non-resonant laser photodetachment.
LEGEND is the successor of the GERDA and MAJORANA DEMONSTRATOR experiments searching for neutrinoless double beta decay. An observation would imply both the Majorana nature of neutrinos and the violation of lepton number conservation, with important consequences for the understanding of the neutrino mass scale, and the matter-antimatter asymmetry in the Universe. The first experimental phase, currently under construction at LNGS, will increase the discovery sensitivity to half-lifes of more than 10e27 yr by employing 200 kg of high-purity Ge detectors enriched in the isotope Ge-76. In a second stage with around 1000 kg of enriched detectors, the ultimate goal of a discovery sensitivity exceeding 10e28 yr will be reachable.
The Alpha Magnetic Spectrometer is operating on the International Space Station since May 2011. So far, it has collected more than 170 billion cosmic-ray events and measured the fluxes of cosmic-ray nuclei up to Silicon (Z=14) and lately of Iron (Z=26) with unprecedented precision providing new and crucial information for cosmic-ray models . In this contribution, I will present the ongoing analysis on the sub-iron elements (from Z=21 to Z=25) and on nickel nuclei (Z=28).
The XENONnT detector recently started its commissioning phase at Laboratori Nazionali del Gran Sasso. Utilizing 5.9 tonnes of liquid xenon (LXe) as active target and designed for a high level of background reduction, it will greatly improve the results of its predecessor, XENON1T. Although primarily a dark matter detector for direct detection of Weakly Interacting Massive Particles, other channels such as the neutrinoless double beta decay and the standing excess of electronic recoil events observed in XENON1T data will play an important role in XENONnT future analysis.
In this talk, I will present an overview of the XENONnT detector, its subsystems, and its main physics goals.
Numerical simulations for cosmic-ray propagation through the Galaxy are important e.g. for understanding the diffuse $\gamma$-ray emission seen by different experiments. Up to now, the source distributions used as input for such simulations are often relying on analytical functionals rather than individual, observation-based sources.
Here, we investigate the impact of cosmic-ray source distributions produced by combining sources observed with the H.E.S.S. experiment and simulated random sources, which follow the matter density in the Galaxy. We show the impact of different realisations of source distributions on the local $\gamma$-ray emission, simulated using the PICARD code.
IceCube, a large telescope of high-energy astrophysical neutrinos, has significantly contributed to our understanding of the Universe. After the discovery of a diffuse flux in 2013 and the detection of a high-energy event coincident with a flaring blazar in 2017, hints of potential sources are now being unveiled by recent analyses. Here we focus on the results of a time-integrated and a time-dependent analysis of 10 years of IceCube data. These analyses are used to test a catalog of gamma-ray emitters, that provides the evidence for a cumulative excess of neutrinos, and to perform an unbiased search of the entire sky.
Fanaroff Riley (FR) 0 radio galaxies form a low luminosity extension of the well-established ultrahigh energy cosmic ray (UHECR) accelerators FR-1 and FR-2 galaxies. Their higher number density makes them interesting candidate sources for an isotropic contribution to the observed UHECR flux. Here, acceleration and survival of UHECR in prevailing conditions of the FR-0 environment are discussed.
The photon target fields are composed of a jet and a host galaxy component, based on multi-wavelength data from the FR0CAT. This allows to simulate all relevant UHECRs loss processes.
We show that FR-0 galaxies can contribute to the UHECR flux in a hybrid scenario based on Fermi-I order and gradual shear acceleration.
In this contribution, we describe the multi-wavelength behavior of Mrk501 from 2017 to 2020, when a very low VHE flux was observed. Alongside the monitoring campaign, three NuSTAR observations were conducted displaying three different low-activity flux levels. This dataset enables us to study multi-wavelength variability and correlations in detail, and allows to identify a historically low X-ray and VHE gamma-ray emission period lasting two years, which could be regarded as the baseline emission for Mrk501. We use the low-activity broadband spectral energy distribution and published IceCube data to investigate the potential hadronic nature of the baseline component, and compare different theoretical scenarios for the evolution of the broadband SED data
We investigate the relationship between quantum correlations and the communication of quantum bits of information. We go beyond standard qubits and instead consider a more general notion of informational restriction which makes no reference to the dimension of Hilbert space. We show how to characterise such informationally restricted quantum correlations and how they qualitatively go beyond standard qubits. Finally, we discuss how this concept both accommodates and provides an alternative perspective on well-known concepts such as Bell nonlocality, quantum contextuality and quantum dense-coding.
Developing novel quantum technology exhibits the challenge of their efficient characterisation. We introduce and experimentally demonstrate a methodology to automatically formulate and select Hamiltonian models, learning the most appropriate in reproducing the observed system’s dynamics. Here, we propose and experimentally demonstrate the quantum model learning agent (QMLA), a Bayesian approach based upon the generation and exploration of alternative, parametrised models; and additional a frequentist approach. To test our methodology, we use the Hamiltonian describing a nitrogen-vacancy-centre electron spin interacting with a spin bath.
In this talk I will describe a quantum-classical variational protocol for learning the structure of the Entanglement Hamiltonian (EH) in Quantum Simulation experiments. In this approach, spatial deformations of the many-body Hamiltonian, physically realized on the quantum device, serve as an efficient variational ansatz for a local EH. On-device spectroscopy of the learned Hamiltonian provides a tool to characterize complex quantum phases. I will discuss advantages over classical learning protocols and will provide prospects that Hamiltonian learning can serve as a tool for verifying quantum simulators in a regime inaccessible to classical simulations.
Ensembles of cold atoms and ions excell in metrology and quantum information processing. This opens the opportunity to utilize tailored, programmable entanglement generation to approach the 'optimal quantum sensor'. Here we report first quantum enhancement in metrology beyond squeezing through low-depth, variational quantum circuits searching for optimal input states and measurement operators. We perform entanglement-enhanced Ramsey interferometry using a Bayesian approach to stochastic phase estimation tailored to the sensor platform. We verify the performance by both directly using theory predictions of optimal parameters, and performing online feedback optimization to 'self-calibrate' the variational parameters. We find that variational circuits outperform classical, and direct spin squeezing strategies under realistic noise and imperfections.
Variational quantum algorithms (VQAs) have become an indispensable tool for noisy near-term quantum computation, enabling small-scale simulations on present-day hardware. So far, however, their success was mainly limited to optimization problems. The go-to method for dynamics remains Trotter-evolution, relying on deep circuits and thus hampered by the substantial limitations of available quantum technology. Despite the development of VQAs for dynamics, their capabilities and feasibility are yet to be assessed. In this study, we investigate the potential of this technique by simulating a spin-boson model in different physical regimes and under varying levels of hardware noise. Furthermore, we compare to Trotter-evolution and make scaling predictions for both algorithms.
I will introduce a "coherence equality" that, in the spirit of Bell's inequalities, can be used to discriminate between classical and quantum resources. This equality is satisfied by any classical communication (localized carrier), but is violated when the carrier is in a quantum superposition of communication directions. This implies that the classical success probability of a certain communication task is always equal to 1/2. Yet, we develop two simple quantum schemes that systematically deviate violate the coherence equality. Such a violation can also be exploited as an operational way to witness spatial quantum superpositions without requiring the use of an interferometer, but only by means of spatially separated local measurements.
It is usually believed that coarse-graining of quantum correlations leads to classical correlations in the macroscopic limit. Such a principle, known as macroscopic locality, has been proved for correlations arising from independent and identically distributed (IID) entangled pairs. In this work we consider the generic (non-IID) scenario. We find that the Hilbert space structure of quantum theory can be preserved in the macroscopic limit. This leads directly to a Bell violation for coarse-grained collective measurements, thus breaking the principle of macroscopic locality.
Actinide-based metal-organic complexes and coordination architectures encompass intriguing properties and functionalities, but are still largely unexplored on surfaces. We report the first in situ synthesis of actinide tetrapyrrole complexes under ultra-high vacuum conditions, both on Ag(111) and h-BN/Cu(111) supports. Exposing a tetraphenylporphyrin (TPP) multilayer to an elemental beam of thorium followed by a temperature-programmed reaction and desorption of surplus molecules yields bis(porphyrinato)thorium (ThTPP$_2$) assemblies. The resulting complexes were characterized by x-ray photoelectron spectroscopy, scanning tunneling microscopy and spectroscopy, temperature-programmed desorption, and complementary density functional theory modeling. Our results give insight into the supramolecular assemblies of ThTPP$_2$ and highlight the conformational and electronic properties of these double-decker compounds with submolecular precision.
The structure and orientation of 5,14-dihydro-5,7,12,14-tetraazapentacene (DHTAP) layers deposited on Cu(110) was studied using reflectance difference spectroscopy (RDS), Scanning Tunneling Microscopy (STM) and Low Energy Electron Diffraction (LEED). The evolution of the RDS signal allows to identify the sequential formation of up to three monolayers as well as a phase transition upon completion of the first one. DHTAP molecules in the first monolayer are always lying flat with their long molecular axis aligned parallel to the [-110]-direction of the Cu(110) surface. However, for subsequent layers the orientation critically depends on the deposition temperature.
Molecular motors that convert external energy into controlled motion have seen great developments in the last decades. While many studies exist in solution, little is known how these functional molecules behave on surfaces. However, such solid support is advantageous as it offers a fixed point of reference and confinement in two dimensions, making the study of the directionality of their motions easier.
We have studied single so-called Feringa motors on Cu(111) by low-temperature scanning tunnelling microscopy (STM). Rotations of individual molecules can be induced over long distances by voltage pulses with the STM tip. Importantly, these rotations show high directionality, which are discussed regarding their specific chemical structure and adsorption.
In this study the growth and energy level alignment of the rod-like, long chain acene heptacene on a Cu(110) surface is evaluated. Our results show that the orientation of the 7A molecules can be controlled by the preparation conditions. Our combined experimental and computational results show that for heptacene oriented along the Cu rows, the lowest unoccupied molecular orbital (LUMO) and the LUMO+1 are occupied. The LUMO+1 receives no charge for molecules aligned perpendicular to the Cu rows. The possibility to tune the energy level alignment and charge transfer at organic-metal interfaces by means of adjustable molecular alignment is fully corroborated by our experiments and density functional calculations.
Self-metalation of 2H-tetraphenyl porphyrins (2H-TPP) on MgO thin films only occurs following charge transfer from the underlying surface. However, it is not clear whether the charging of the molecules is directly responsible for the metalation, or rather the charge-induced repositioning of the macrocycles.
Comparing the behavior of 2H-TPP with that of porphyne (2H-P) by angular resolved photoemission spectroscopy and scanning tunneling microscopy, we have investigated the role of the macrocycles on the metalation.
We observed that 2H-P molecules self-metalated regardless of their charge state, demonstrating that the key factor in enabling the self-metalation of porphyrines on MgO is the proximity of the nitrogen atoms to the underlying surface.
2D metal-organic networks show great promise for applications in catalysis, gas sensing or electronics. Ascertaining fundamental intrinsic properties of such systems requires their synthesis on weakly-interacting substrates. Here, we show Fe-TCNQ networks self-assembled on graphene/Ir(111), studied experimentally by Low Energy Electron Microscopy (LEEM), Scanning Tunneling Microscopy (STM) and X-Ray Photoemission Spectroscopy (XPS). A single Fe-TCNQ structure is present in three non-equivalent orientations on the graphene substrate; symmetry operations lead to observation of fifteen rotational domains. The network is thermally stable up to ca. 550 °C, making this an ideal model system for fundamental studies of single-atom reactivity or charge transfer induced phenomena.
Indium oxide (In$_2$O$_3$) is a ubiquitous anode material in OLEDs and photovoltaics due to its transmissivity to visible light and metal-like conductivity (when doped with Sn). When In$_2$O$_3$ is paired with organic materials, a thin organic buffer layer is often introduced to improve the charge injection from In$_2$O$_3$ to the organic active layers. We probe the adsorption behaviour and density of states (DOS) of the prototypical copper phthalocyanine (CuPc) - In$_2$O$_3$ interface combining scanning tunnelling microscopy, non-contact atomic force microscopy and local tunnelling spectroscopy. Starting from the clean In$_2$O$_3$(111) surface we identify morphological details of the molecular structures and their electronic properties and compare the results to DFT calculations.
With the increasing average global temperature more and more households need a way to cool down. This study explores biomimetic passive cooling utilizing structured surfaces. The focus is put on structures that lower a body's average temperature without using electricity or replenishable resources. Biomimetics helps to find non-polluting ways to achieve such cooling structures.
At first, the physical principles will be explained, accompanied with current studies about their implementation. Biomimetics and its importance for this thesis will be discussed. Some examples found in nature will be explained. Possible attempts to use those will be expatiated. Finally, a summary will be given with an outlook about the future of passive cooling.
The public lecture will also be streamed under the following link:
https://lms.uibk.ac.at/url/RepositoryEntry/5058101302?guest=true&lang=de
The detection of exoplanets orbiting other stars has revolutionized our view of the cosmos. First results suggest that it is teeming with a fascinating diversity of rocky planets, including those in the habitable zone. Even our closest star, Proxima Centauri, harbors a small planet in its habitable zone, Proxima b. With upcoming telescopes, we will be able to peer into the atmospheres of rocky planets and get a glimpse into other worlds. Using our own planet and its wide range of biota as a Rosetta stone, I will discuss the possibilities and challenges to explore how we could detect habitability and signs of life on exoplanets over interstellar distances.
The discussion on what makes a planet a habitat and how to detect signs of life is lively. This talk will show the latest results, the challenges of how to identify and characterize such habitable worlds, and how near-future telescopes will revolutionize the field. For the first time in human history, we have developed the technology to detect potential habitable worlds. Finding thousands of exoplanets has taken the field of comparative planetology beyond the Solar System.
Particle physics research has a long tradition of making scientific advancement through large-scale collaborative efforts. With the unprecedented scale of CERN’s Large Hadron Collider came a real need for extensive efforts in communication, education, and outreach. The International Particle Physics Outreach Group (IPPOG) was formed in 1997 as a European initiative (then EPPOG) to become an international player with the development of the International Particle Physics Masterclass programme. IPPOG became a scientific collaboration in 2016 with 30 countries, six experiments, CERN and two associate members participating. IPPOG brings new discoveries to young people and to the public at large and has evolved as a strategic pillar of particle physics.
Throughout the centuries, the relation between science and its publics has undergone significant transformations. The talk will trace some of these transformations for the case of physics. It begins with 17th century England and the importance of gentlemen for the conduct of experiments. The 19th century, by contrast, witnesses scientific institutions develop a clear separation from the lay public. With physics laboratories devising outreach programs and scientific controversies receiving wide public attention, the current situation is open to interpretation. Will physics increasingly open up to public participation? And how do the media and public respond?
The Future Circular Collider (FCC) program, proposed at CERN, consists of a luminosity-frontier electron-positron collider (FCC-ee) as first stage, followed by an energy-frontier hadron collider (FCC-hh) as second stage, and promises the most far-reaching physics program for the post-LHC era. FCC-ee is a precision instrument to study the Z, W, Higgs and top particles, and offers unprecedented sensitivity to signs of new physics. Most of the FCC-ee infrastructure can later be reused for the subsequent hadron collider, FCC-hh. The FCC-hh provides proton-proton collisions at a centre-of-mass energy of 100 TeV and can directly produce new particles with masses of up to several tens of TeV.
The 2020 Update of the European Strategy requests a feasibility study of the FCC colliders and related infrastructure to be established as a global endeavor and completed on the timescale of the next Strategy update by 2026. This presentation will summarize the status of infrastructure studies and the conceptual designs of FCC-ee and FCC-hh, covering the machine concepts, the R&D for key technologies, and a possible implementation schedule.
Neural-Network quantum states (NQS) have been recently proposed as a method to solve challenging interacting quantum problems. During this talk, I will discuss the application of NQS to a variety of problems. First, we consider how NQS can be used to obtain excited states as well ground states within a symmetry sector. Next, building on the tools developed, we apply the NQS approach to frustrated J1-J2 model on the square lattice. Here, we show that deep convolutional NQS can achieve results that are competitive with other state of the art variational methods developed in the past decade. Finally, we present results on the use of NQS for quantum chemistry.
Van der Waals (vdW) heterostructure attracted wide attention by the research community in the past decade. Their functionality depends predominantly on two dimensional (2D) materials. However, there are other vdW heterostructure building blocks besides 2D sheets, as molecular crystals.
This talk will focus on vdW heterostructures combining organic crystallites and 2D materials. By epitaxially growing small rod-like molecules on 2D materials, effectively one-dimensional needle-like crystallites form and self-align to the substrate’s high symmetry directions [1]. Originating from highly anisotropic properties of the organic molecules, these mixed-dimensional vdW heterostructures exhibit unique mechanical and opto-electronic properties [2,3].
Isotopic ratios of radioactive releases into the environment are useful signatures for contamination source identification. The atomic 233U / 236U ratio analysed in representative environmental samples by Accelerator Mass Spectrometry showed ratios of (0.1-3.7)·10-2. The ratios detected in compartments of the environment affected by releases of nuclear power production or by weapons fallout differ by one order of magnitude. Significant amounts of 233U were only released in nuclear weapons fallout, either produced by fast neutron capture on 235U or directly by 233U fuelled devices. This makes the 233U / 236U ratio a promising new fingerprint for radioactive emissions, which may serve as a superior oceanographic tracer as Uranium behaves conservatively in sea water. Our findings indicate a higher release of 233U before the maximum of global fallout in 1963, setting constraints on the design of the nuclear weapons employed.
Over the last few years, several discrepancies with respect to Standard Model predictions have arisen in charged- and neutral-current semileptonic B meson decays. These measurements include indications of lepton universality violation, which if confirmed would be a clear signature of physics beyond the Standard Model. I will review the experimental status of these anomalies at LHCb, as well as the prospects for the future.
The Poster Session is held on Tue and Thu. All posters are to be presented on both days. However, due to technical reasons, the contributions are only listed in the timetable of Tue.
Quantum tunneling reactions can play a significant role in chemistry, and hydrogenic systems allow for first-principles calculations. The rate of the tunneling reaction H$^2$ + D$^- \rightarrow$ HD + H$^-$, for which the collision complex is closely related to the H$^-_3$ anion, has been calculated but has lacked verification. Here we present high-sensitivity measurements of the reaction rate carried out in a cryogenic 22-pole ion trap. We model the effect of a high-energy tail in the velocity distribution to investigate its influence on the reaction rate. Our measured value agrees with quantum tunneling calculations, serving as a benchmark for molecular theory.
Tracing ultrafast processes induced by interaction of light with matter is often very challenging. In molecular systems, the initially created electronic coherence becomes damped by nuclear rearrangement on a femtosecond timescale which makes observations of electron dynamics in molecules particularly difficult. We demonstrate that the attosecond transient absorption spectroscopy (ATAS) can be a very useful technique to trace such ultrafast processes. We report the application of ATAS to probe the oscillations of the positive charge created after ionization of the propiolic acid molecule. By taking advantage of element-specific core-to-valence transitions, we show that the resolution of ATAS makes it possible to trace the dynamics of electron density with atomic resolution.
The main goal of the project is to find a machine learning approximation for the kinetic energy functional of orbital-free density functional theory,
\begin{equation}
T[n] = \int \tau[n] \,\mathrm{d}x,
\end{equation}
where the function $\tau[n]$ is represented using a feed forward neural network. Since it is known that the function $\tau$ is translationally invariant and non-local, i.e. a function of the values of $n$ at various positions $x$, the structure of a convolutional neural network seems like a reasonable choice.
Quantum chemistry has become an important tool to analyze and predict the properties of molecules. Coupled cluster (CCSD(T)) is considered to be the gold standard as it gives accurate results and can be improved in a well-known manner, but is computationally expensive. If one wants to compute the properties of molecules containing heavy elements relativistic contributions need to be included and require a 2- or 4-component treatment for accurate results. This increases the amount of memory and floating point operations. Supercomputers provide such resources, but are heterogeneous systems with various memory spaces and processing units. An implementation of relativistic coupled cluster for such infrastructures will be presented, see also https://arxiv.org/abs/2103.08473.
Recently, stacked sheets of nanoporous graphene have been suggested for the separation of racemic mixtures with respect to molecular chirality. Different pore arrangements lead to different barrier heights for the two enantiomers of a given molecule. We are investigating the performance of these membranes via a combination of a recent force-field ansatz of the Grimme group with nudged-elastic-band calculations. First, the energy barriers for methane and nitrogen are calculated for different pore sizes and arrangements. Probabilities for propagation are studied via molecular dynamics and compared to predictions based on transition state theory. Second, we investigate chiral separation tendencies in the case of D- and L-Leucine.
Chiral topological semimetals are a new class of topological matter that host chiral multifold fermions in a chiral crystal structure. These new fermionic quasiparticles can be viewed as a higher spin generalization of Weyl fermions without equivalence in elementary particle physics. Their large topological charge has been predicted to give rise to unusual phenomena, such as giant quantized photocurrents, long fermi-arc surface states, unusual magnetotransport signatures, new spin-orbit torques, or unconventional and topological superconductivity. Whilst there have been many theoretical predictions related to multifold fermions in previous years, they have so far remained elusive in experiments.
Here I will report the experimental observation of multifold fermions in a chiral topological semimetal. Using angle-resolved photoelectron spectroscopy, we directly visualize their long fermi-arc surface states and resolve a band splitting that indicates that they carry the largest topological charge that can be realized for quasiparticles in any material. We are also able to show experimentally that there is a direct relationship between the handedness of the crystal structure and the electronic chirality (i.e. the Chern number sign) of the multifold fermions, which indicates that structural chirality can be used as a control parameter to manipulate phenomena that are sensitive to the electronic chirality, such as the direction of topological photocurrents. I will then also present our latest experimental results about new directions in the field of chiral topological semimetals.
Time-periodic Floquet drive is a powerful method to engineer quantum phases of matter, including fundamentally nonequilibrium states that cannot be realized in static Hamiltonian systems. A characteristic example is the anomalous Floquet topological insulator, which exhibits a unique topologically protected nonequilibrium transport phenomenon: nonadiabatic quantized charge pumping. We study the fate of this phenomenon in the presence of time-dependent noise, which breaks the protecting Floquet symmetry. Surprisingly, we find that the charge pumped per cycle remains quantized up to a finite noise amplitude. We trace this robustness of Floquet topology to an interplay between diffusion and Pauli blocking of the decay of chiral edge states.
We investigate triple nodal points, i.e., three-fold degeneracies of energy bands in the momentum space of three-dimensional crystalline solids. First, based on the symmetries required for their stability, we develop a classification of triple nodal points in weakly spin-orbit-coupled materials. Second, by combining the derived classification with symmetry indicators for corner charges, we find that pairs of triple points in semimetals are associated with monopole charges and higher-order topology. The higher-order bulk-boundary correspondence of such triple-point pairs is a quantized fractional jump in the momentum dependence of the electric charge localized at the crystal hinges. I will illustrate these results using first-principles calculations for the compound Sc$_3$AlC in applied strain.
We enrich the notions of stable and fragile topology by introducing delicate topological insulators: band structures possessing topological invariants that can be trivialized through an addition of a trivial conduction band. We find that although delicate topological insulators are Wannier representable with exponentially-localized symmetry-preserving Wannier functions, they can possess a different type of obstruction to an atomic limit. Namely, impossibility to localize all Wannier functions to one unit cell, i.e. multicellularity. In this talk, I will explain the concepts of delicacy and multicellularity on a toy-example and discuss their observable consequences.
We employ the Ensemble Geometric Phase (EGP) - a generalisation of the Zak phase to mixed states - to analyse the topology of an open Su-Schrieffer-Heeger model involving both unitary Hamiltonian dynamics and dissipative coupling. For dissipation described by the Lindblad formalism, we discover regimes where the EGP is quantised to zero or pi, and relate the quantisation to the existence of an inversion symmetry. Furthermore, we devise topological charge pumping protocols by sequentially tuning hopping and system-bath couplings and realising an interplay between unitary dynamics and dissipation. We investigate the fate of this quantisation to situations of finite temperature through the Redfield master equation.
Recent theoretical works unveiled that crystalline symmetries can stabilize topologically fragile Bloch bands that challenge our very notion of topology: one can trivialize these bands through the addition of trivial Bloch bands. Here, we show via auxiliary-field Monte Carlo simulations how fragile topology enhances the superfluid weight and hence the superconducting critical temperature. This feature is particularly relevant in flat-band systems where the conventional contribution to the superfluid weight vanishes and might explain the high transition temperature observed in magic-angle twisted bilayer graphene.
In preparation for the High-Luminosity upgrade of the Large Hadron Collider, the ATLAS detector will be upgraded in 2025-2027. Its new Inner Tracker (ITk) Pixel detector is designed to cope with 200 interactions per bunch crossing, which produces a digital output of up to 11Tb/s. A new data transmission chain, able to transmit such a high data rate in the high-radiation environment has been developed. In this talk I present the prototyping and testing steps, that we took to complete the ITk Pixel data transmission chain, adding all the components from the front-end chip to the readout card.
The operation of the LHC beyond 2026, which aims to reach luminosities around 5-7.5 x 1034 cm-2s-1 , poses new challenges for the CMS detector. Therefore, the Phase-2 upgrade of CMS will completely replace the tracking system including more advanced silicon sensors/electronics which can sustain higher radiation levels and ensure efficient tracking performance. Studying and testing the properties and performance of the new Outer Tracker silicon strip sensors is a crucial process which precedes the module assembly. The 200 m2 sensor series production is in progress, thus some first results of the sensors quality, their design and the expected performance as defined in the prototyping phase, will be summarized.
The CMS phase-2 upgrade, necessary to cope with the radiation levels and pileup of the High-Luminosity LHC, requires a finer granularity, radiation-tolerant endcap calorimeter. This is achieved by 600 m^2 of silicon sensors as detector material for the highly radiated regions, together with scintillator tiles with individual SiPM readout. To reduce the cost, a new 8-inch wafer process is used, posing new challenges for prototyping and production.
This talk covers the prototyping of the 8-inch process for highly radiation tolerant, large-area, DC-coupled silicon sensors, together with tools for high-throughput, non-destructive characterization via a dedicated test structure system.
The Electromagnetic Calorimeter (ECAL) of the CMS experiment at CERN is a hermetic, fine grained, homogeneous calorimeter made of about 75,848 lead tungstate scintillating crystals. During the Run 1 and Run 2 operations of the Large Hadron Collider of CERN, the CMS ECAL played a key role in the discovery of the Standard Model Higgs Boson. In order to cope with ∼140 pileup events expected for the High Luminosity upgrade of the LHC (HL-LHC), a new design of the CMS ECAL will be needed. Future challenges of the ECAL will be presented in this talk motivating the evolution of the design to maintain its performance during the HL-LHC data-taking.
A new scintillating-fibre (SciFi) tracker is being installed and commissioned as part of the ongoing LHCb upgrade. As a consequence of the radiation the over-all light yield of the detector will be reduced in the course of LHC Run 3, compromising the hit detection efficiency. The inner modules will thus be replaced during the next long shutdown (2025–2027). For this occasion, a development of silicon photomultiplier arrays with micro-lenses has been started in order to improve the photon detection efficiency. The results of a ray-tracing simulation study, predicting up to 20% higher light yield, as well as measurements performed on first prototypes will be presented.
The SND@LHC (Scattering and Neutrino Detector at the LHC) is a recently approved neutrino and feebly interacting particles search experiment, based at CERN.
It is located 480 m away from the ATLAS interaction point and consists of a target region built of emulsion-tungsten walls interleaved by scintillating fibre planes, a hadronic calorimeter built of scintillating bars and iron absorbers, and a muon identification system.
All scintillators are read out by silicon photomultipliers and a custom read-out electronics based on the TOFPET2 ASIC, allowing for signal discrimination and amplitude and time measurement.
The talk will discuss the structure of the data acquisition system and on the amplitude and time measurement performance.
In view of the High Luminosity phase of the Large Hadron Collider the ATLAS experiment will upgrade its Inner Detector replacing it with an full-silicon Inner Tracker (ITk). The modules of this pixel detector will output data at a high data rate, each module producing up to 5.12 Gb/s. The ITk Pixel data transmission chain features an opto-electrical conversion system (Optosystem) powered by a two-stage powering system. This talk will present the Optosystem's powering concept, the tests aimed at its validation and the setup that will be used for quality assurance of the Optosystem powering.
The CMS Phase-1 pixel detector has been operated successfully during the course of the LHC Run 2, ended in 2018. In order to allow to maintain the excellent performance during Run 3 (starting in 2022), the innermost barrel layer has been replaced with new modules, assembled and tested at PSI during the LHC shutdown.
This contribution provides an overview of the CMS Phase-1 pixel detector, reports on the recent replacement of its innermost layer, and discusses the commissioning and calibration of the detector towards the imminent restart of operations.
Ultracold neutrons (UCN) with kinetic energies below 300 neV can be confined for hundreds of seconds, making them ideal for experiments that benefit from long observation times. One of these experiments at the Paul Scherrer Institute (PSI) searches for the CP violating permanent neutron electric dipole moment, probing beyond Standard Model physics. Such precision experiments with UCN are statistics limited. There are worldwide efforts to improve the output of UCN sources. At PSI, comparing simulations of the neutron flux in the deuterium moderator with UCN measurements has lead to new insights into mechanisms limiting UCN extraction. Modified freezing procedures reduce thermal stress in the solid deuterium, increasing the UCN output.
An experiment at PSI, carried out by the muX collaboration, aims to measure the nuclear charge radii of radioactive elements such as $\mathrm{^{226}Ra}$ and $\mathrm{^{248}Cm}$ with muonic atoms. An intermediate test performed with $\mathrm{^{185,187}Re}$ targets in 2016 led to the extraction of their spectroscopic quadrupole moments. Typical muonic spectroscopy experiments require targets of several grams. Restrictions applying to radioactive targets limit their usage to μg-quantities where the direct muon capture cannot be accomplished. A technique to transfer muons to μg targets has been developed by the muX collaboration employing a pressure cell with a $\mathrm{100\,bar}$ $\mathrm{D_2/H_2}$ gas mixture. In this contribution, the current status of the muX experiment is presented.
Currently PSI delivers the most intense continuous muon beam in the world with up to few 10^8 μ+/s. The High Intensity Muon Beam (HiMB) project aims at developing a new target station and muon beam lines able to deliver up to 10^10 μ+/s, with a huge impact for low-energy, high-precision muon based searches.
To do so, the focus is on two key points: increasing the surface muon production efficiency, thanks to geometrical optimization of the target and increasing the capture and transmission of the muons, using a solenoid-based beam line design. We present the current status of the HiMB project.
Due to negligible synchrotron radiation, muon colliders have been considered a promising tool for new discoveries. A hot hadronic shower serves as a muon source. However, the large emittance of the produced beams poses a critical challenge for the design of muon colliders which require high-charge and dense muon beams. The only feasible way to reduce this emittance within the muons’ short lifetime is based on the principle of ionization cooling. A final cooling scheme provides a gradual emittance reduction by the means of specific absorbers inside high-field magnets. In this work, the previous simulation studies are extended by optimizing the final emittance to the optimal values.
The Paul Scherrer Institute (PSI) provides the world's highest intensity DC muon beam of $\mathcal{O}(10^{8})\,\mu^{+}/$s at 28$\,$MeV/c. The muCool collaboration is developing a device which converts such a beam of cm-size and MeV-energy into a low-energy beam of sub-mm size and 1$\,$eV energy spread by achieving a compression of the 6-dimensional phase space by 10 orders of magnitude with a prospected efficiency of $10^{-3}$. In this talk, the working principle of the muCool device and the results from the 2019 beam time are presented. Supported by SNF project 200020_172639.
I will introduce here the MuMASS experiment, aiming to improve the current results on the Muonium Lamb Shift and the 1S-2S frequency measurements by orders of magnitude. I will present our most recent results of the Lamb Shift determination, which could already set competitive limits on New Physics, in particular on possible CPT and Lorentz violations. I will conclude with the current state of our Muonium 1S-2S experiment, focusing on the latest tests of the detection system.
Muonium (M) atoms are interesting for a diverse palette of experiments reaching from precision spectroscopy to muon beam cooling and anti-matter gravity. We have been investigating new M emitters at room temperature. For the room-temperature study we have developed three compact experimental setups in order to compare vacuum yields and dynamic properties of various emitters. The setups pursue complementary approaches including scintillator bars and Micromegas tracking detectors for the decay positrons as well as a scintillator based atomic electron detector. In this talk we present the developed setups together with our findings about novel muonium emitters at room temperature.
Just like their classical counterparts, quantum algorithms require a set of inputs, provided for example as real numbers, and a list of operations to be performed on some reference initial state. Unlike classical computers, however, information is stored in a quantum processor in the form of a wavefunction, thus requiring special procedures to read out the final results. In fact, it is in general neither possible nor convenient to fully reconstruct this quantum state, so that useful insights must be extracted by performing specific observations.
Unfortunately, the number of measurements required for many popular applications is known to grow unsustainably large with the size of the system, even when only partial information is needed. This is for example the case for the so-called Variational Quantum Eigensolver, which is based on the reconstruction of average energies. In this talk I will discuss a novel scheme to tackle this problem.
We employ a generalised class of quantum measurements that can be iteratively adapted to minimize the number of times the target quantum state should be prepared and observed. As the algorithm proceeds, it reuses previous measurement outcomes to adjust its own settings and increase the accuracy of subsequent runs. We make the most out of every sample by combining all data produced while fine-tuning the measurement into a single, highly accurate estimate of the energy, thus decreasing the expected runtime by several orders of magnitude. Furthermore, all the measurement data contain complete information about the state: once collected, they can be reused again and again to calculate any other property of the system without additional costs.
As quantum technologies advance, the ability to generate increasingly large quantum states has experienced rapid development. In this context, the verification of large entangled systems represents one of the main challenges in the employment of such systems for reliable quantum information processing. Though the most complete technique is undoubtedly full tomography, the inherent exponential increase of experimental and post-processing resources with system size makes this approach infeasible at even moderate scales. Other methods aiming at probing only certain properties of the system such as entanglement detection via witness operators generally demand much less effort, but still consume large number of copies for reliable estimates, which may go beyond the reach of the large-scale regime. For this reason, there is currently an urgent need to develop novel techniques that surpass these limitations. In this talk I will review novel techniques focusing on a fixed number of resources (sampling complexity), and thus prove suitable for systems of arbitrary dimension. Specifically, a probabilistic framework requiring at best only a single copy for entanglement detection is reviewed, together with the concept of selective quantum state tomography, which enables the estimation of arbitrary elements of an unknown state with a number of copies that is low and independent of the system's size. These hyper-efficient techniques define a dimension demarcation for partial tomography and opens a path for novel applications.
Characteristic impedance in superconducting quantum circuits determines whether the ground state wavefunction is dominated by charge or phase fluctuations. The crossover occurs at RQ = 6.45 kΩ above which the charge fluctuations are suppressed below 2e-. Most interesting is the behavior of the Josephson junction (JJ), which acts as a non-linear inductor at low impedance and as a non-linear capacitor in the opposite limit. We explore this limit by shunting the JJ with a geometric inductor formed a superconducting high density planar coil. This element maintains a single uninterrupted wavefunction and offers high reproducibility, linearity and the ability to couple qubits magnetically.
Physicists have been fascinated by the non-equilibrium dynamics of quantum systems for a long time. Microscopic details are relevant at the early stage of the time dynamics where the system has just begun thermalizing. However, at the onset of thermal equilibrium, the dynamics are governed by symmetries and topology, and at this stage, classical hydrodynamics is expected to emerge. In this talk, we will report experimental measurements of quantum to classical hydrodynamics crossover observed in a long-range interacting spin system containing 51 trapped ions. By varying the range of our spin-spin interaction and by measuring the spatio-temporal correlations, we will show normal diffusion to superdiffusion transport, described by Lévy flights.
IONICON Analytik is the market leader for highly sensitive real-time trace gas analyzers (PTR-MS) with many potential applications. The company was founded in 1998 as a spin-off of the University of Innsbruck with the sale of the first system, built by scientists for scientists. We have constantly improved the system’s performance for cutting edge scientific research (Lab) and its usability and robustness for automated industrial applications (Fab).
We will discuss the challenges and milestones on our journey towards new research applications and markets for routine analysis e.g. the semiconductor manufacturing or a recently developed COVID-19 breath test using PTR-MS.
The challenges of our modern society require the development of novel sensors for the rapid detection and quantification of chemicals. We developed an uncooled infrared (IR) detector based on nanoelectromechanical sensing (NEMS) where resonators made of silicon nitride act as highly sensitive platforms for photothermal sensing. NEMILIE combines air filtering and nebulization techniques to allow the direct sampling and measurements of water (nanoplastics, pesticides,...) and airborne (viruses, nanoparticles, pollution,...) contaminants at the picogram level. By adding a broad spectral absorber, NEMILIE LIGHT can be further used as a multipurpose room temperature detector operating close to the photon-noise limit.
Basel Precision Instruments GmbH (BASPI) is a young spin-off of the Zumbühl Group at the University of Basel in Switzerland. Our vision is to provide a better lens into the quantum world by enabling researchers to minimize noise, achieve lower temperatures and maximize stability in their experiments. Over one hundred laboratories across the globe are already using BASPI's instruments in ultra-low temperature, quantum transport, scanning microscopy and numerous other experiments. BASPI's current product portfolio includes current and voltage preamplifiers and (DAC) voltage sources with the highest available resolution and best available noise performance and cryogenic microwave filters.
Perovskite quantum dots (PQDs) can improve applications from displays to scintillators because of their superior light-emitting properties compared to classical quantum dots. Standing in the way of these applications is the difficulty to process PQDs into devices, especially into the polymer thin films used in displays and scintillators, without losing their unique properties. BrightComSol presents BrightLeaf™, a flexible perovskite-based scintillator based on a new resin, BrightSplash™. Our resin allows for the efficient processing of PQD flexible films at low and high loading. We share recent highlights of using BrightLeaf™ for high-resolution X-ray imaging.
The company usePAT was founded in early 2018, it offers the application of ultrasonic fields to support industrial in-line measurements. A decade of interdisciplinary research collaboration between a group from the Faculty of Physics (sensors and ultrasound) and the Faculty of Chemistry (process analysis) preceded the foundation. The commercialisation opportunity has emerged over the years in particular because companies have repeatedly been brought into contact with the technology. Today, a spin-off company with about ten employees already showing initial market successes exists.
The lecture will deal with the research and the foundation’s history as well as the relationship between the two.
Concerning the commercialization of Intellectual Property and the facilitation and backing of spin-offs, the University of Innsbruck is among the most active and most experienced Universities in Austria. In this talk, you will hear how this topic developed since the 1980s and will get valuable and encouraging insights how to improve your “entrepreneurial mindset” and how to transfer your research results to successful products and services.
Nanoparticles comprising three different materials in a core@shell@shell configuration are synthesized in cold helium droplets by sequential doping. Rhodamine B molecules form complexes in helium droplets that give rise to a strong fluorescence upon laser excitation, enabling an in situ investigation of the synthesized structures. In the presence of a Au core, fluorescence from the rhodamine B shell is quenched due to excitation transfer from excited molecules to the Au particle. The addition of an intermediate hexane layer inhibits the contact between Au core and rhodamine B shell, which results in the recovery of the fluorescence.
High performance synthetic fibers are increasingly applied in fields where they might be exposed to elevated temperatures. Above a critical temperature, Tc, however, they lose their mechanical properties resulting in unexpected failure under load. To enable a passive sensor monitoring the temperature history, we introduce a method to functionalize polymer fibers with ultrathin thermochromic optical coatings by Magnetron sputtering based on chalcogenide phase change materials. The optical contrast for the amorphous-to-crystalline transition of GeSbTe (GST) upon heating to Tc was enhanced by reflectors. We found, that the color change can be adjusted by the Ge content to the demanded temperature range matching Tc of industrially important polymer fibers.
Lithium fluoride (LiF) is an interesting material for spintronic applications[1] and a potential candidate for decoupling single-molecule magnets from metallic substrates.[2] We have investigated the growth and morphology of LiF deposited onto the Ag(100) surface in the monolayer regime under different conditions. Scanning tunneling microscopy, low energy electron diffraction and polarized X-ray absorption spectroscopy reveal that LiF exhibits epitaxial Volmer-Weber type growth. When the substrate is held at room temperature during growth, anisotropic and strained dendrites form, while at 500 K LiF self-assembles into more relaxed square islands displaying a Moiré pattern.
[1] Drew et al., Nature Materials, 8, 109 (2009); [2] Wäckerlin et al., Advanced Materials, 28, 5142 (2016).
Recently, CdO has been proposed as a very promising material for IR plasmonics due to its high plasma frequency and low damping. However, low propagation lengths and broad minima are common limitations with CdO surface plasmons.
To overcome these limitations, we propose the use of thin high quality crystalline CdZnO layers grown on sapphire substrate. Hybrid surface modes arise from the interaction between the high energy phonons of the sapphire and CdZnO surface plasmons. Here, we design and realize gold gratings to such CdZnO layers and successfully couple mid-IR light with these hybrid modes and discuss their potential applications.
A current-driven source of long-range
surface plasmons (LRSPs) on a duplex metal nanolayer
is reported. Electrical excitation of LRSPs was experimentally
observed in a planar structure, where an
organic light-emitting film was sandwiched between two
metal nanolayers that served as electrodes. To achieve
the LRSP propagation in these metal nanolayers at the
interface with air, the light-emitting structure was bordered
by a one-dimensional photonic crystal (PC) on
the other side. The dispersion of the light emitted by
such a hybrid PC/organic-light-emitting-diode structure
(PC/OLED) comprising two thin metal electrodes was
obtained, with a clearly identified LRSP resonance peak.
Electronic structure of heterointerfaces plays a pivotal role in their device functionality. Recently, ultrathin films of superconducting NbN have been integrated by MBE with the semiconducting GaN. We use soft X-ray angle-resolved photoelectron spectroscopy (ARPES) to directly measure the momentum-resolved electronic structure and band offsets at this Schottky heterointerface as well as the band-bending profile into GaN. We support the experimental findings with first-principles calculations as well as transport and optical measurements. The Fermi states in NbN are found to align against the band gap in GaN, excluding any electronic cross-talk of the superconducting states in NbN to GaN. This finding opens prospects of integrating superconducting devices into semiconductor technology.
Successful implementation of cutting-edge flexible devices in various branches of modern life requires the synthesis of efficient materials with advanced properties. We address this challenge by mixing Al, Cu, and Ga via vacuum co-deposition applying the combinatorial libraries approach. Systematic screening of maximum current density and voltage, film thickness, and composition reveals the prominent potential of Al-Ga and Cu-Ga alloys of certain concentrations for replacing conventional interconnects materials in flexible electronic devices due to their more than 100% improved ability to withstand electromigration and enhanced adhesion to a PEN-based substrate. In-detail TEM characterization of the contacts with superior performance highlights the self-healing effect of polycrystalline film grain-boundaries wetted by Ga.
High power consumption represents a major bottleneck for conventional transistor technologies (MOSFETs), due to the inability of further reducing supply voltage while simultaneously limiting the off-state leakage current. This limitation can be overcome by Tunnel FETs, a novel transistor concept based on the quantum-mechanical band-to-band tunneling. During my PhD research, I demonstrated the first hybrid technology platform combining III-V Tunnel FETs and MOSFETs with a scalable process and suitable for large-scale semiconductor manufacturing. Such low-power technology platform paves the way to future energy efficient electronics, with the ultimate goal to reduce the carbon footprint of the ICT industry.
In this contribution, we discuss the catalytic formation of NH3 using radiofrequency (RF) N2-H2 plasmas and a tungsten (W) foil. A parametric study was done at various RF powers (30–300 W), discharge pressures (2–5 Pa), gas compositions (10–90% N2) and discharge temperatures (< 673 K). NH3 generally increased with the electron density and/or electron temperature, whereas the discharge temperature had a minor effect. We observed no impact on NH3 after contaminating the W surface with H2, N2 and O2. Instead, coating the W foil with a nm-thick boron layer led to a reduction of ammonia by half, possibly due to the formation of B-H bonds.
The First Mirrors (FMs) in ITER diagnostic systems would be subject to deposition of material from the first wall (Be and W), which would severely compromise their optical properties. For a restoration, they would be routinely cleaned using RF discharges. The FMs would also be DC-grounded via a RF quarter wavelength filter, which significantly increases the plasma potential (from 30 V to over 100 V). This leads to an increased sputtering of the walls as well as their deposition on the FMs, reducing the plasma cleaning efficiency. In this contribution, we discuss various strategies experimented in ITER relevant mockup, to minimize wall sputtering and enhance plasma cleaning of DC-grounded FMs.
Metallic first mirrors will be close to the fusion plasma in ITER and might suffer from erosion and deposition coming from the first walls of the fusion reactor. Consequently, the optical diagnostics system can be compromised. The most promising in-situ technique to remove these deposits while restoring the mirrors optical properties is plasma sputtering. This contribution discusses the evolution of the optical properties of rhodium-coated mirrors upon cycles of depositing Al2O3 followed by its removal using argon radiofrequency plasma. Within an acceptable margin, the optical properties of the mirrors were shown to be conserved up to 100 cycles.
Atoms of antihydrogen can be formed by slowly merging cryogenic positron and antiproton plasmas. The ASACUSA collaboration will measure the ground state hyperfine splitting of these atoms, using a sextupole magnet to analyze the atoms after they pass through a microwave spin-flip cavity. This spectroscopy beamline has been tested with ordinary hydrogen, achieving ppb precision. The remaining technical challenge is the production of a sufficiently intense beam of antihydrogen. In this talk I will describe the ongoing efforts to (1) achieve cold, dense plasmas and (2) characterize the quantum state distribution of the atoms produced by recombination in the plasmas.
The control of plasma position and shape is fundamental to achieve high performance in fusion tokamaks. This work compares different approaches for the simulation of the plasma evolution coupled to controller dynamics: FGE (Forward free-boundary Grad-Shafranov Evolutive code), FGElin (FGE linearised version) and RZIp, all implemented as part of the same tokamak simulation suite MEQ. FGE solves the full Grad-Shafranov equilibrium equation, while RZIp considers only semi-rigid motions of the plasma, considerably reducing the number of states. The basic equations and assumptions are illustrated and a comparison between the performances of the codes is presented. Possibilities towards a real-time estimation of the vertical instability growth rate with RZIp are explored.
Gas discharges in transparent electrodes have been investigated in a double-cathode coaxial cylindrical system. Optimal working conditions for the discharges have been established. Spectral measurements of the optical emission have been performed to obtain discharge geometry and distribution profiles of the populations of excited and ionized gas particles. A well-defined less luminous plasma double layer has been observed surrounding a plasma fireball, tangent to a luminous space charged formation inside the inner cylinder. A peak has been observed at the end of the cylinders, both for temperature and for density. The cathode system is investigated to understand basic plasma physical processes.
We present control over the emitted state of quantum cascade laser frequency combs through strong radio-frequency modulation close to their repetition frequency. In particular, coherent broadening of the spectrum from about 20 cm$^{-1}$ to 60cm$^{-1}$ can be achieved throughout the DC-current dynamical range. Close to the free-running beatnote frequency, tuning of the modulation frequency results in tuning of the spectral bandwidth and center-frequency. By switching between modulation frequencies we can multiplex spectral regions with negligible overlap from the same device at rates of at least 20 kHz. In the time-domain, we are able to transition from quasi-continuous to pulsed ($\tau_p \approx 55$ ps) output by injecting at high power.
Hydrogen (H2) is widely considered as an ideal CO2-free energy carrier. Physisorption in nanoporous carbons is a promising way for reversible H2 storage at pressure below 100 bar. The gravimetric amount of stored H2 strongly depends on the nanopore structure, notably the mean pore size being typically below one nanometer. Yet the mechanisms which determine the storage capacity are still not fully understood. Here we present in-situ small-angle neutron scattering data of H2 adsorption in nanoporous carbons at low pressures up to 1 bar, and discuss the influence of pore structure on the density distribution of the adsorbed H2.
As wireless near-IR telecommunications through air and space are reaching their performance-limitations in terms of bandwidth and transmission under turbulent conditions, solutions for low-atmospheric attenuation data transmission are sought. Quantum-cascade-based systems offer such capabilities, i.e. intrinsically high GHz-modulation properties and robust free-space transmission by addressing the long-wavelength infrared region of 8-12µm.
A novel InGaAs/InAlAs/InP QCD for the 9-10µm range as crucial building-block of a monolithic-integrated heterodyne detection system is presented. We show the comparison of differently sized 15-vs-1 period ridge-waveguides and analyze their spectral photocurrent while comparing their performance in terms of sensitivity, spectral responsivity, detector noise etc. The goal is to distinguish the best candidate for a heterodyne sensor.
The longwave-infrared holds various applications ranging from sensing and imaging to optical free-space communication. The increasing demand for miniaturized systems requires the development of compact photonic networks between on-chip optoelectronic components such as lasers, detectors and modulators. To resolve this challenging task, we introduce and experimentally demonstrate a novel type of broadband semiconductor-metal surface-plasmon-polariton waveguide, consisting of a Ge-on-Au structure. It shows total waveguide losses as low as 10.5 dB/mm at 9.5 μm, which remain <20 dB/mm for the entire spectral range between 6–12 μm. This paves the way for a wide range of on-chip applications using novel longwave-infrared integrated systems.
There exists a growing interest in the properties of the light generated by hybrid systems as a means of providing nanoscale sources of quantum light. Specifically, plasmonic nanocavities have been shown to retain and enhance excitonic nonlinearities even when the number of emitters is large. In these platforms, photon antibunching is generally achieved by coupling one or several emitters to a single dipole mode. Nevertheless, plasmonic nanocavities present a richer photonic structure, and the presence of various cavity modes may bring new possibilities in the generation of photon correlations. Here, we study the quantum statistics of the light scattered from a nanoparticle-on-mirror cavity filled with a single quantum emitter.
Quantum Cascade Random Lasers (QCRLs) feature a broadband gain medium as well as a broadband cavity, which makes them ideal for spectroscopic applications. However, due to mode competition and spatial hole-burning, only discrete modes arise in reality.
The full potential of QCRLs can be reached by perturbing them optically. We present such an optical perturbation scheme, which by the help of deep learning allows for the instantaneous creation of custom emission spectra.
The project has aimed to investigate digital models of photovoltaic (PV) modules and to describe PV modules’ behavior under different failure modes. The modeling of the modules and other components is mainly performed by physical models. The model approach considers the integration of artificial failures representing equivalent classes of failure types in a real diode, enabling a better understanding of how deviations add up to diode characteristics in varying systems. The complete digital models will describe PV behavior in a simulated environment for a physical counterpart. The models, which will be transferrable to different module types and technologies, will allow prediction- and the design of behavior of different PV systems.
For a long time, the sole function of a luminaire was to illuminate its surrounding. Nowadays, with the rise of light-emitting diode (LED) based luminaires also functionalities beyond illumination become more and more of relevance. Recent attempts in this regard focus on communication, localization and, most recently, backscattered visible light sensing. Here we demonstrate and discuss system designs, which allow for tunable artificial light (dimming, color temperature variation) that performs communication and sensing tasks (like identification and speed detection of moving objects) in parallel, and outline the potentials of tailored intelligent optical surfaces to further advance visible light backscatter technologies.
The NUCLEUS experiments aims to perform a high-precision measurement of the coherent elastic neutrino–nucleus scattering (CEvNS) at the EdF Chooz B nuclear power plant in France.
CEvNS is a unique process to study neutrino properties and to search for new physics beyond the Standard Model. NUCLEUS is based on cryogenic detectors, operated at temperature of the order of 10 mK, with nuclear-recoil energy thresholds at 10 eV scale.
This talk will present the design of the experiment and its status and will give a glimpse of its physics potential.
NA64 is a high-intensity frontier experiment running at the CERN SPS. NA64 searches for possible candidates of mediators between the dark sector and the standard model by looking for missing energy events in an active beam dump. I will present the latest results of NA64 running in electron mode setting constraints in the mass-coupling parameter space for the vector and the axion portals to the dark sector as well as for possible new generic bosons. This year we will resume data taking and aim to deliver an unprecedented sensitivity to new physics thanks to increased statistics, better detectors and improved setups.
NA64$\mu$ aims at searching for light dark sector particles weakly coupled to muons at the CERN SPS. These searches are sensitive to dark photons in a mass region larger than 0.1 GeV, which is not accessible with NA64e. The combination of both experiments will allow to completely explore the very interesting thermal light dark matter parameter space. NA64$\mu$ will be also sensitive to $Z’$ bosons in the MeV-GeV mass range which could additionally provide an explanation for the recently confirmed (g-2) muon anomaly. In this talk, I will describe the status of the approved 2021 pilot run and NA64$\mu$ future prospects.
The Strongly Interacting Massive Particle (SIMP) paradigm provides dark matter (DM) candidates as pseudo-Goldstone bound states of dark fermions under a new gauge group. Freeze-out then occurs through $3\to2$ dark matter self-annihilation and points to DM masses of $O(100~\text{MeV})$. We study the spectrum of the lightest mesons of $Sp(4)$ gauge theory with $2$ fundamental Dirac fermions using lattice gauge theory. There are $5$ pseudo-Goldstone bosons which can self-annihilate. We investigate the explicit breaking of the flavour symmetry and report that one pseudo-Goldstone is lighter than the others which are still mass-degenerate.
ArDM is the only dual-phase tonne-scale liquid Argon Dark Matter detector for the direct search of Weakly Interacting Massive Particles (WIMPs). The scintillation light and ionization charge produced by recoiling nuclei in WIMP‐Argon collisions can be measured independently. The WIMP/neutron-induced nuclear recoils can be discriminated from the electron/photon background via the pulse shape of the scintillation light and the respective charge-to-light ratio. After successful data-taking ArDM stopped operating in 2020 and 3.5 billion dual-phase events are now subject of analysis. In this talk, the basic working and analysis principle will be explained. The detailed discrimination methods and an outlook to the future of experiments such as ArDM will be presented.
This Fall the upgrade of the antiproton decelerator, the Extra Low ENergy Antiproton (ELENA) ring, will start operation at CERN opening a new era for antihydrogen research. In the context of the GBAR experiment aiming to study the gravitational behaviour of antimatter, our group from ETHZ proposed and is preparing a Lamb shift measurement of antihydrogen with an uncertainty of $100~\mathrm{ppm}$. This will allow to extract the antiproton charge radius at a level of $10\%$ and will provide a sensitive test of Lorentz and CPT symmetry. I will present the results of the setup commissioning with hydrogen atoms and plans for the upcoming beamtime with antiprotons.
Black Holes are one of the most interesting consequences of Einstein's general relativity. Since their theoretical prediction they have engendered a lot of research, both theoretically and experimentally. However, to this day, many aspects of black holes are not sufficiently well understood. One such aspect is the origin of their huge gravitational entropy. In this talk, I will explain how the idea of holography can help us to better understand this problem.
At present R-matrix analyses are widely performed in order to obtain a good representation of the experimental data, especially for light nuclear systems. A versatile R-matrix code with several non-standard capabilities was developed and successfully applied to experimental data. However, the standard R-matrix method can only be applied for binary reactions. Breakup channels, which may occur in light nuclear systems at rather low energies, can only be treated via approximations. In this contribution we present a novel R-matrix formalism for three-body breakup channels based on the Faddeev equations. The method has been numerical implemented and first applications will be presented.
In 2012, the ATLAS and CMS Collaborations announced the discovery of a new state with a mass around 125 GeV, compatible with the Standard Model Higgs boson.
In 2018, the Higgs boson to bottom quark coupling was observed with a significance of 5.6 sigma using the full Run 1+2016+2017 data by the CMS collaboration.
Further precision measurements of the Higgs boson coupling to bottom quark are currently being studied. This talk focuses on the latest update by the CMS Collaboration of measurements of the Higgs boson production with an associated vector boson where the vector boson decays leptonically and the Higgs boson decays to a pair of bottom quarks.
The $t\bar{t}\gamma$ cross-section is measured at a center-of-mass energy of $13~\text{TeV}$, using a data-set corresponding to an integrated luminosity of $137~\text{fb}^{-1}$, recorded by the CMS experiment. Events with an isolated, highly energetic lepton, at least three jets from the hadronization of quarks, among which at least one is b-tagged, and with one isolated photon are selected. The inclusive cross-section for a photon with $\text{p}_\text{T}\geq~20~\text{GeV}$ and $|\eta|<1.4442$, is measured to be $800~\pm~7~\text{(stat)}~\pm~46~\text{(syst)}~\text{fb}$, in good agreement with the standard model prediction. The measurement is carried out differentially in several kinematic observables and interpreted in the framework of the standard model effective field theory, leading to the most stringent direct limits to date.
Resonant production of physics beyond the standard model can be probed up to the TeV scale by the experiments at the LHC. Until now, no indication of new physics was found at these high energies. Complementary to direct searches, indirect effects of new physics at even higher energy scales can be studied in the model independent framework of effective field theories(EFTs).
Due to its mass, the top quark plays a crucial role in the electroweak sector of the standard model. This makes top quark processes suitable for EFT interpretations. In this talk, recent EFT measurements performed by the CMS Collaboration are presented that set a focus on top quark physics.
A generalized extension of the standard model of particle physics (SM), known as standard model effective field theory (SMEFT), consists of all the possible operators of dimensions greater than four, satisfying the symmetries of the SM Lagrangian. SMEFT operators, which systematically parameterize the impact of physics beyond the SM in a model-independent way, modify the production and decay kinematics of the Higgs boson compared with those predicted by the SM. I will discuss the techniques used by the CMS experiment to constrain the SMEFT operators in the Higgs sector and report the corresponding results.
The relation between the top quark mass parameters of Monte-Carlo event generators and renormalized and well-defined Lagrangian masses is not very well understood and a subject of intense discussions in the community given that the current experimental uncertainties in direct top mass determinations is at the level of 300 MeV.
In this presentation I talk about preliminary results where the top quark mass parameters in the major Monte-Carlo event generators Pythia, Herwig and Sherpa are numerically calibrated to the pole mass and the MSR mass. The results quantify the different meanings of the top mass parameters in the different Monte-Carlo generators.
Statistical modelling is a key element in many parts of physics, especially in High-Energy Physics (HEP). zfit is a Python library for unbinned, likelihood model fitting. Its main computational backend is TensorFlow, an easy-to-use, highly scalable computing library similar to Numpy. zfit provides a high level interface for advanced model building and fitting while also designed with a unified interface to be easily extendable, allowing the usage of custom and cutting-edge developments from the scientific Python ecosystem in a transparent way.
This talk presents zfit and its usability for data analyses in physics, especially in HEP, as well as recent developments and improvements to the library.
In the presentation I intend to give an overview of the one-loop/one-emission and two-loop contributions required for soft gluon evolution and the resummation of non-global logarithms at the next logarithmic order. I will present the general structure of the soft anomalous dimension matrix in the colour-flow basis and highlight the importance of three-parton correlations which appear at two-loop order beyond the usual dipole picture. Using the Feynman tree theorem a flexible formulation of the loop integrals in terms of the emission's phase space can be found in an algorithmic setup.
Machine learning has become increasingly popular in physics over the last decade. Recently, big efforts have been made to incorporate global and gauge symmetries in different neural network architectures. In this talk, I will focus on translational symmetry, which is an important idea behind Convolutional Neural Networks (CNNs). After explaining possible ways to ensure translational equivariance in a CNN, I will present two other architecture types that break translational equivariance at different places in the network. I will show how these architecture types perform on supervised machine learning tasks on a complex scalar field on the lattice, especially concerning their generalization ability to different physical parameters and lattice sizes.
In ultra-thin media, the phase-matching condition for nonlinear optical processes, such as four-wave mixing (FWM), relaxes. We characterize the resulting broadband biphoton states by stimulated emission tomography and present progress towards photon pair generation in ultra-thin carbon nanotube films. Our 200 nm thick single-walled carbon nanotube film (much smaller than the pump wavelength of around 810 nm) imposes energy conservation as the only requirement in the nonlinear interaction. The absence of phase-matching entails that the photon pairs are highly entangled in frequency and separable in all other degrees of freedom.
Using stimulated emission tomography we characterize the joint spectral intensity of the generated biphoton state. We keep the pump wavelength constant and stimulate the FWM process with different wavelengths. The measured spectral width of the state extends over more than 50 THz. This result shows the potential to generate photon pairs with broadband entanglement with application in particular in the field of quantum communication, such as demonstration of entanglement distribution.
I will discuss the recent proposal of a set of experimentally accessible conditions for detecting entanglement in mixed states based on comparing moments of the partially transposed density operator. The union of all inequalities reproduces the Peres-Horodecki criterion. Exploiting symmetries can help to further improve their detection capabilities and the estimation of the inequalities is based on local random measurements in single-copy experiments. We show how to include the experimentally relevant situation of non-identical (but independent) copies (drifts) in the analysis and derive error bounds and confidence intervals as a function of the number of performed measurements.
The double slit experiment provides a demarcation between classical and quantum theory, while multi-slit experiments demarcate quantum and higher-order interference theories. In this work we show that these experiments pertain to a broader class of processes, which can be formulated as information-processing tasks. We provide a connection between the order of interference and the probabilities of successfully achieving the given tasks. Furthermore, we prove the order of interference to be additive under composition of systems both in classical and quantum theory. Finally, we extend our game formulation within the generalized probabilistic framework and prove that tomographic locality implies the additivity of the order of interference under composition.
Bell's theorem shows that no hidden-variable model can explain the measurement statistics of a quantum system shared between two parties, thus ruling out a classical (local) understanding of nature. In this work we demonstrate that by relaxing the positivity restriction in the hidden-variable probability distribution it is possible to derive quasiprobabilistic Bell inequalities whose sharp upper bound is written in terms of a negativity witness of said distribution. This provides an analytic solution for the amount of negativity necessary to violate the CHSH inequality by an arbitrary amount, therefore revealing the amount of negativity required to emulate the quantum statistics in a Bell test.
Next-generation quantum sensors are expected to outperform classical sensors. Since the success of these quantum sensors depends on the efficient use of limited resources (such as probe states and coherence time), we introduce the paradigm of smart quantum sensors, i.e., quantum sensors which make autonomous adjustments in order to optimize the measurement precision and to save resources. A suitable framework for smart quantum sensors is provided by the adaptive Bayesian approach to parameter estimation. We train neural networks to become fast and strong experiment-design heuristics that are shown to outperform established heuristics for the technologically important example of frequency estimation of a qubit that suffers from dephasing.
In this talk, I will discuss the so-called device independent quantum key distribution (DIQKD) protocols -- where all elements of the setup are analysed as black boxes. Contrary to standard QKD, the security of DIQDK does not rely on detailed quantum models of the devices and is proof against "quantum hacking". After a concise introduction I will present some ideas (noisy preprocessing, full-statistics analysis, random key measurements) that help bridging the gap between experimental requirements of DIQKD and current technological capabilities. Finally, we will discuss finite statistics analysis and the perspectives of long distance DIQKD based on SPDC generated entangled photons. The talk is based on publications given in comments.
Deep neural networks have had a profound impact on the field of reinforcement learning by achieving unprecedented performance in challenging decision-making tasks. Almost in parallel, the idea that variational quantum circuits could be used in quantum-classical machine learning systems started gaining increasing traction. Such hybrid systems have already shown the potential to tackle real-world tasks in supervised and generative learning, and recent works have established their provable advantages in artificial tasks. Yet, in the case of reinforcement learning, which is arguably most challenging, no proposal has been successful in solving standard benchmarking problems, nor has the potential of hybrid models been made clear. In this work, we resolve both questions.
We discuss the emergence of a moderate biased error in non-ideal integrated photonic circuits. We investigate its correlation with properties of the optical paths, revealing potential issues for high-precision tests and optical implementations of machine learning.
Since 2008 Optotune has developed multiple pioneering product lines, which include tunable optical devices, such as lenses, mirrors, and prisms as well as beam modulation devices for enhancing image resolution, speckle reduction or dynamic beam deflection. Optotune's technologies are sold to industrial and consumer markets and are used in applications ranging from machine vision to projection. Dr. Wolfgang Zesch is Principle Development Engineer and Technical Product Manager at Optotune. He will present on some examples how pioneering optical technologies for the fast-paced industrial and consumer markets are developed.
With a background in Physics and Engineering the four students Susanne, Florian, Alex, and Luis founded the start-up Holo-Light in 2015. The extended reality (XR) company specializes in immersive technologies and has created groundbreaking solutions for the enterprise market. Holo-Light’s remote rendering software component ISAR enables users to stream entire big data XR applications in real-time. The company also provides AR 3S Pro, a powerful XR software, enabling engineers to work and collaborate on 3D CAD data. In creating new ways of experiencing and working with 3D content – Holo-Light is on its way to enable the future of mobile computing. CEO and Co-Founder Florian Haspinger will share the backstory.
The world is experiencing a quantum revolution with astonishing potential for innovation. We present here a new quantum microscope based on NV center technology and show how it's already used today to advance research in materials science and spintronics. We review challenges specific to developing quantum technologies and highlight further opportunities in quantum sensing.
I will outline the development of the spin-out ParityQC from the first patent as a PostDoc to the venture capital based foundation of the company. ParityQC is a spin-out of the University of Innsbruck and the Austrian Academy of Sciences established in 2019. The company is based on the invention of the Parity Quantum Computing architecture which allows for solving optimization problems on quantum devices. ParityQC works with hardware developers world wide, including US, Japan and EU. The company also developed ParityOS, the operating system to run the ParityQC architecture.
Building on top of more than 20 years of research and development at the University of Innsbruck and the Austrian Academy of Sciences, the startup AQT has realized the first 19'' rack-based ion-trap quantum computer. The system has demonstrated control of up to 50 ions, is offering fault-tolerant gate performance and cloud-access. The realized stand-alone solutions, in particular the high-performance ion trap, are available to support your various research applications ranging from metrology via quantum communication to simulation and quantum computation.
The transfer is done by public transportation. Tram departure at the stop "Technik". For detailed information see the black board at the registration desk.
Only for participants who have registered and paid in advance. On-site registration is not possible.
The albedo of a celestial body is the fraction of incident starlight reflected by it. The study of the albedos of Solar System objects is at least a century old, at least in the Western world. As examples: Bond (1861) speculated on the near-unity albedo of Jupiter, while Russell (1916) observed the opposition surge of the Moon near and at full phase. The light of a planet or moon varying with orbital phase is known as its phase curve. Modern astronomical facilities have enabled the measurement of phase curves of reflected light and thermal emission from exoplanets (e.g. Kepler, TESS, CHEOPS, Hubble, Spitzer), which enables the investigation of atmospheric dynamics and aerosols. In the current talk, I will concisely review and discuss historically important work, including seminal contributions by Lommel (1887), Seeliger (1888), Chandrasekhar (1960), Sobolev (1975) and Hapke (1981). These introductions set the stage for a detailed discussion of our recent work on generalising these classic works to derive closed-form, ab initio solutions for the geometric albedo and reflected light phase curve. This novel theoretical framework is applied to Kepler space telescope data of the hot Jupiter Kepler-7b, where we demonstrate that one may infer fundamental aerosol (single-scattering albedo, scattering asymmetry factor) and atmospheric (geometric albedo, Bond albedo, phase integral) properties from precise photometry alone, thus providing powerful complementary information to spectra. Another case study are the Cassini phase curves of Jupiter, which were measured in the early 2000s by the Cassini space mission but never subjected to Bayesian inference. By inverting the Cassini phase curves, we infer that aerosols in the Jovian atmosphere are large, irregular, polydisperse particles that may be responsible for causing coherent backscattering of sunlight.
Timelines from first idea to reimbursed product / therapy / indication, during which translational research from bench to bedside has to be performed, are typically long in the field of sensorineural active implants. The most widespread of these implants is the Cochlear Implant (CI) which restores hearing in deaf people of all ages through electrical stimulation of the auditory nerve. Translational research has resulted in 4 newer categories of the CI in addition to the classic CI for the completely deaf: the Combined CI (electric and acoustic stimulation, electric and mechanical stimulation or vestibular and electric stimulation), the Individualized CI (based on preoperative imaging, anatomical, audiometric, electrophysiological and other evaluations the best suited electrode and surgical approach are selected), the augmented CI (a CI that can elute dexamethasone and other substances from the electrode into the cochlea) and the fully implantable CI, for which a human pilot study is ongoing. All of the above implant systems have high degrees of conditional MRI-safety by now. They also provide connectivity and wireless audio streaming possibilities. Based on the technology of our CI other sensorineural implant systems are being developed for a variety of conditions that limit quality of life.
This session is public and will also be streamed under the following link:
https://lms.uibk.ac.at/url/RepositoryEntry/5058101302?guest=true&lang=de
With his three laws on planetary motion, Johannes Kepler (1571-1630) laid the foundations of modern astrophysics. He discovered them at Prague at the beginning of the 17th century when he compiled the Rudolfinean Tables, a collection for astronomical calculations. They were based on data from Tycho Brahe's (1546-1601) large astronomical observatory on the island of Hven. Third in the group was Jost Bürgi (1552-1632), who, through his scientific instruments and calculation methods, had contributed to the accurate measurements in the observatory at Kassel and who came to Prague in 1604.
In the lecture the interaction of these three scientists with their very different backgrounds and abilities will be studied.
Johannes Kepler was the first who described the motions of the planets correctly. He no longer considered circular orbits but he introduced elliptical orbits which was quite revolutionary at his time.
The orbits can be described by his famous three laws. In this lecture we mainly consider Kepler’s third law. It enables us to determine one of the most important parameters in Astrophysics, the mass. The mass of a star determines its evolution but it can be only inferred from perturbation by another mass, such is the case for exoplanets, double stars.
We give several examples of stellar mass determinations and then address to motions of stars close to the galactic center. How can we observe those motions and what are the conclusions from those. The next step then is to consider a whole galaxy and to test whether Kepler’s third law accurately describes the motion of galactic orbits. This led to the postulation of dark matter. Finally, the dynamics of galaxy clusters is reviewed and their velocity dispersion also shows a clear deviation from Kepler’s third law.
Thus Kepler’s laws are fundamental for mass determination and the observed deviations led to fascinating new ideas about the structure of the universe.
The question, if it is possible to generate SF6$^{+}$ and to keep it stable until it can be observed has been the purpose of numerous experiments. Embedding the molecule in positively charged helium nanodroplets answers finally this question. High resolution mass spectrometry reveals not only the ion surrounded with helium, with further experimental techniques the evaporation process of the helium can be investigated until pure SF6$^{+}$ is visible in the mass spectra. This result indicates that the present experiment enables the investigation of various fragile ions that have been invisible for the scientific community so far.
2-deoxy-2-fluoro-D-glucose (FDG) is a glucose analog with the hydroxyl group at C2-position replaced by a fluorine atom and has been proposed as a potential radiosensitizer. Herein we present our findings on electron-induced dissociations in FDG upon low-energy electron attachment in the gas phase using a crossed electron/molecular beam setup. The experiment was carried out within the energy range of 0–12 eV. We observe the formation of negative ions from several fragmentation pathways, which are mostly associated with multiple bond cleavages within the FDG molecule. The most abundant anion was found to be C3H3O2-. The experimental results are supported by quantum chemical calculations.
Building on our recent report on the production of stable, highly charged droplets of superfluid helium, a new experimental method was designed to investigate chemical reactions in the sub-kelvin environment with a significantly higher ion yield compared to previous setups. We demonstrate a novel method of softly ionizing dopant molecules by proton transfer, while largely preventing fragmentation, even for notoriously delicate molecules. Recent measurements indicate promising results while studying the influence of sodium atoms doped onto PAHs on their ability to reversibly attach H2 molecules.
Polycyclic aromatic hydrocarbons (PAHs) are isolated in multiply charged helium nanodroplets (HNDs). The charged dopant molecules are again liberated from the droplets upon collision with a stainless-steel surface, but remain decorated with up to several tens of helium (He) atoms. Action spectroscopy is performed on these He tagged species. A tunable pulsed laser is used for excitation and ion yields are recorded with a reflectron type time-of-flight mass spectrometer (TOF-MS). The recorded absorption spectra are compared to astronomical observations in order to identify possible carriers of diffuse interstellar bands (DIBs).
The amide compound formamide (CH3NO; FA) is a smallest molecule with a peptide bond and is an important biological precursor. Previous dissociative electron attachment studies with deuterated derivatives of FA in gas phase showed that this compound can act as an agent for electron-induced surface functionalisation of hydrogen-terminated materials. In the present study, we investigated the formation of clusters of bare and hydrated FA upon electron interaction, using a crossed electron-cluster beam experiment. We report the formation of bare FA cluster ions up to the hexamer and different FA-H2O clusters upon micro-hydration of FA.
Charge-transfer processes, particularly in salt clusters, depend sensitively on the chemical environment. Studying such charge-transfer behaviour is ideally suited to gas-phase clusters, whereby the size and chemical composition can be controlled. To understand these charge-transfer processes at a molecular level, laser spectroscopic measurements in the ultraviolet and visible region are utilised, focussing on ionic salt systems. Electrospray ionization is employed producing salt clusters, which are stored in the cell of a Fourier transform ion cyclotron resonance mass spectrometer. Laser systems provide tuneable laser light in the 225–2600 nm region. For each size-selected cluster, evaporation of stoichiometric and non-stoichiometric fragments are recorded, elucidating photochemical pathways connected to charge-transfer transitions.
Electron capture by molecules leads to the formation of transient negative ions, which may dissociate through dissociative electron attachment (DEA). DEA to the 1-bromoacetyl-3,3-dinitroazetidin (RRx-001) molecule in the gas phase has been studied utilizing a crossed electron-molecular beam setup combined with a quadrupole mass spectrometer. RRx-001 has been proposed as a radiosensitizer. We observed 11 fragment anions, which indicate that low-energy electrons with kinetic energies ranging from 0 to 14 eV strongly decompose the molecule. The results indicate efficient formation of NO2– and Br– upon DEA to RRx-001.
Nitrofurans have been used as antibiotics or antimicrobials in human and veterinary medicine. The underlying mechanism is ascribed to the reduction of the nitro group by nitro reductases, producing the electrophilic intermediates nitroso and hydroxylamine, which are capable of binding to DNA and other biomolecules in microorganisms. In the present study, we investigated electron attachment to 2-nitrofuran (C4H3NO3) in the electron energy range between ~0-12 eV. For generation of a high-resolution electron beam, a hemispherical electron-monochromator was used. Electron attachment to 2-nitrofuran leads to a large variety of charged fragments and radicals with NO2 - as the most abundant fragment anion. The experimental study was supported by thermochemical threshold calculations.
The anharmonicity of atomic couplings, responsible e.g. for finite heat conductivity in crystals due to phonon-phonon scattering, is most fundamentally accessible as broadenings of phonon dispersions or finite lifetimes.
Here we will compare inelastic neutron scattering on fcc-Al up to the melting point to ab initio calculations of q-dependent line broadenings [1]. Further, an analysis of the atomic interaction constants will show how to construct numerically efficient phenomenological potentials that accurately reproduce anharmonic properties as computed by DFT at very small computational effort, and finally the limitations of perturbation-derived linewidths will be elucidated.
[1] A. Glensk et al., Phys. Rev. Lett. 123, 235501 (2019)
In low-dimensional semiconducting nanostructures, strong confinement leads to quantization of charges allowing to investigate and control their individual physical properties. Particulary, one-dimensional semiconducting nanowires have attracted a lot of attention as hosts of spin-qubits or, in combination with superconducting leads, as hosts of Andreev levels and Majorana bound states. Here, we present a novel approach to investigate semiconducting nanowires, where we couple capacitively to a superconducting on-chip resonator. We report results on our most recent experiments where we have individually coupled a high-impedance, magnetic-field resilient NbTiN resonators to both a Ge/Si core/shell nanowire, and an InAs nanowire with superconducting leads.
We describe the discovery of ice XIX based on neutron diffraction, Raman spectroscopy, calorimetry and dielectric spectroscopy and study transitions in its hydrogen sublattice. The high-pressure ice polymorph crystallises in a √2 x √2 x 1 supercell with respect to the parent ice VI phase in space group P-4, where the water molecules are partially antiferroelectrically ordered. At ambient pressure, ice XIX experiences the first order-order transition known in ice physics to its sibling ice XV. This represents the first case for an oxygen atom lattice in which two types of hydrogen order are experimentally realised.
Long lived quasi-stationary states (QSSs) are a signature characteristic of long-range interacting systems both in the classical and in the quantum realms. Despite their ubiquity, the fundamental mechanism at their root remains unknown. Here, we show that the spectrum of systems with power-law decaying couplings remains discrete up to the thermodynamic limit. Then, several traditional results on the chaotic nature of the spectrum in many-body quantum systems are not satisfied in presence of long-range interactions. In particular, the existence of QSSs may be traced back the finiteness of Poincar\'e recurrence times. This picture justifies and extends known results on the anomalous magnetization dynamics in systems with power-law decaying couplings.
The spin-1/2 Heisenberg model on the pyrochlore lattice is debated to possess a spin-liquid ground state. We contest this hypothesis with a numerical investigation using exact diagonalization and variational techniques: RVB-like Monte Carlo ansatz and convolutional neural network for (variational) calculations up to $4×4^3$ spins. We determine the phase transition between the putative spin-liquid phase and the neighboring ordered phase and characterize the ground state in terms of symmetry-breaking. We find indications of spontaneously broken inversion and rotational symmetry, calling the scenario of a featureless quantum spin-liquid into question. This showcases how variational techniques allow to make progress in answering challenging questions about 3D frustrated magnets.
A longstanding goal is to utilize the spin of an electron in electronic devices, both, in applications summarized as spintronics, as well as in fundamental research, for example to demonstrate spin correlations in superconducting electronic elements. To this end, we have introduced ferromagnetic split-gates (FSGs) that allow to individually polarize the electron spin states of semiconductor quantum dots (QDs). Such spin polarized QDs can be used as highly-efficient tunable spin-filters (spin detectors) in complex nanoelectronic devices. Here, we demonstrate a negative spin-corrleation in a Cooper pair splitting (CPS) device using two FSG/QD elements at the two output arms which can be tunned in a parallel and antiparallel spin-filter configuration.
We perform large scale quantum Monte Carlo simulations of the Hubbard model at half filling with a single eight component Dirac cone close to the relativistic quantum critical point. We discuss the implementation of a single Dirac cone in the SLAC formulation for eight Dirac components and its reliability upon the introduction of interactions. The finite size scaling properties of the Hubbard model with a single Dirac cone are shown to be superior compared to the honeycomb lattice. We extract the critical exponents and discuss the origins of the discrepancies of estimates in literature. We find coinciding exponents once honeycomb lattices of linear dimension larger than 15 are considered only.
There is a huge renewed interest in magentotransport phenomena in solids, especially in relation with topology, Berry curvature, and Weyl points. The responses of interest include nonlinear anomalous Hall effect, crystal Hall effect, planar Hall effect, unidirectional magnetoresistance, and electrical magnetochiral anisotropy, among others. In this talk. I will show how to classify all these responses according to their transformation properties under inversion and time-reversal symmetry, and how they can be systematically described by the Boltzmann equation combined with the semiclassical equations of motion modified by Berry curvature and intrinsic magnetic moment of Bloch states - the so-called "Berry-Boltzmann equations".
Non-Hermitian topological phases of open quantum many-body systems are fundamentally dynamical in nature. This poses a challenge to identify robust signatures of non-Hermitian topology and to characterize critical behavior at topological phase transitions. We show that non-Hermitian topology of a driven-dissipative Kitaev chain becomes manifest in crossings in the entanglement spectrum after a quench. The time scale of these crossings diverges at the topological phase transition, which can be crossed either by changing parameters of the Hamiltonian of the system or by increasing the strength of dissipation. We analyze how this dynamical criticality of the entanglement dynamics is affected by long-range hopping and pairing.
Rare-earth nickelates, RNiO$_{3}$, are negative charge-transfer materials with electronic configuration of Ni-3$d^8\underline{L}$ ($\underline{L}$ = oxygen ligand hole) in their metallic state. Most RNiO$_{3}$ undergo low-temperature metal-to-insulator transition (MIT) accompanied by breathing distortion in their crystal structure, where neighboring expanded NiO$_{6}$ octahedra (Ni-3$d^8$ configuration) alternate with collapsed NiO$_{6}$ (Ni-3$d^8\underline{L}^{2}$). Here, using resonant inelastic x-ray scattering, we reveal that the electron-phonon coupling (EPC) of the breathing-mode phonon significantly increases as NdNiO$_{3}$ undergoes MIT. Meanwhile, no significant changes are observed in the EPC of LaNiO$_{3}$ (SmNiO$_{3}$), which stays metallic (insulating) at all studied temperatures. These results confirm the major role that the breathing distortion and its EPC play in the MIT of RNiO$_{3}$.
Given a quantum gate implementing a unitary operation U without any specific description but its dimension, we present a universal quantum circuit that implements its inverse by making k uses of the given operation. We consider probabilistic and deterministic scenarios, in both cases, the performance exponentially approaches to a perfect implementation. The protocols employ an adaptive strategy, proven necessary for the exponential performance. Additionally, we discuss the power and limitations of indefinite causality by analysing the performance of processes where the use of the input-gates does not necessarily respect a definite causal order, a better performance may be obtained.
In order to reject the local hidden variables hypothesis, the usefulness of a Bell inequality can be quantified by how small a p-value it will give for a physical experiment. Here we show that to obtain a small expected p-value it is sufficient to have a large gap between the local and Tsirelson bounds of the Bell inequality, when it is formulated as a nonlocal game. We develop an algorithm for transforming an arbitrary Bell inequality into an equivalent nonlocal game with the largest possible gap. We also present explicit examples of Bell inequalities with gap arbitrarily close to one, and show that this makes it possible to reject local hidden variables in a single shot, without needing to collect statistics.
A fascinating fact about the collective behavior of indistinguishable quantum particles is the existence of only two types of statistics: bosonic and fermionic, characterized by the exchange symmetry of their associated quantum states. So far, all attempts to explain the origin of these symmetries resort on oblivious assumptions added to the abstract quantum formalism (e.g. dimensionality of space). Hereby we introduce an information-theoretic study of particle statistics in the space of abstract modes. We show that there are infinitely many statistics compatible with the unitary symmetry and the Fock space structure, with bosons and fermions as special cases which can be singled out by a set of simple operational principles.
Interference of single particles lies at the core of quantum mechanics. The most prominent demonstration of this effect is the double-slit experiment: a single experimental run indicates an experiment with single particles, however the statistics of repeated runs reassembles interference fringes. This is the source of the celebrated wave-particle duality. In this work we show that classical wave mechanics combined with the statistical detection model can completely reproduce quantum interference experiments with single particles. The recreation of quantum double-slit experiment using classical waves shows that the dual behaviour between waves and particles (at least its part described in this work) is not necessarily proof of a genuine quantum effect.
We consider the Unruh effect for a pointlike multilevel particle detector coupled to a massless real scalar field and moving in a quantum superposition of accelerated trajectories. The state of the detector excitations is, in general, not a mere mixture of the thermal spectrum characteristics of the Unruh effect for each trajectory with well-defined acceleration separately. For certain trajectories and excitations, and upon the measurement of the trajectory state, the state of the detector features in addition off-diagonal terms. The off-diagonal terms of these "superpositions of thermal states" are related to the distinguishability of the different possible states in which the field is left after its interaction with the detector.
Quantum resource theories (QRTs) provide a unified framework for understanding quantum-mechanical properties, but physically well-motivated resources may possess structure whose analysis is mathematically intractable, such as non-uniqueness of maximally resourceful states, non-convexity, and infinite-dimensionality. We systematically study manipulation and quantification of resources in general QRTs under minimal assumptions. We prove general existence of maximally resourceful states. We also discover a novel phenomenon, catalytic replication of resources, where a resource state is infinitely replicable by free operations. Furthermore, we introduce and study notion of consistent resource measures to quantify resources without contradicting asymptotic-state-conversion rate. These establish unified foundation of QRTs applicable to physically well-motivated resources whose analysis can be mathematically intractable.
The large interest from the general public combined with the need to develop the next generation of quantum workforce, set a new challenge for the quantum computing experts: educating a vast public of not expert. Several national and international initiatives focus on education and outreach targeting a broad range of audiences, from high school pupils to developers. In this scenario, Quantum Games represent an hands-on way to explain QC following the principle of “learning by doing”.
We investigate several approaches to explain quantum concepts via games such as puzzles, boardgames, or, for the most creative, providing an user-friendly set of tools for people to make their own first quantum game.
Quantum interference of indistinguishable bosons is indispensable for many quantum optical experiments. As in the famous Hong-Ou-Mandel effect, symmetry of the input state and symmetries in the scattering scenario can lead to destructive interference and the suppression of a large number of output events. The rules specifying which input-output combinations interfere totally destructively are summarized in so-called suppression laws. Here, we experimentally investigate the suppression law of the Jx unitary in a femtosecond laser-written waveguide structure with four photons emitted from a SPDC source. We show that totally destructive interference does not require mutual indistinguishability between all, but only between symmetrically paired particles, in agreement with recent theoretical predictions.
One of the challenges of scaling up quantum processors is the optimization of the quantum gates, as each gate may require different control parameters. We developed and tested a fast protocol to automatically calibrate the entangling 2-qubit Mølmer Sørensen gate using Bayesian parameter estimation. Such a protocol promises to increase experimental uptime by decreasing the time needed for calibration, as well as allowing automated operation. Our protocol achieves a median infidelity of 0.13(1)% caused by miscalibration in $1200+/-500$ experimental shots. This paves the way to decouple quantum circuits from their implementation on ion trap hardware, allowing operation by an end user without detailed knowledge of the physical realization.