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The next annual meeting, again a joint one with the Austrian Physical Society (ÖPG), will take place from 27 - 30 August 2019 at the Universität Zürich (UZH), with pre-conference workshops on Quantum Machine Learning on 26 August. 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 Association MaNEP (Materials with Novel Electronic Properties), the NCCR QSIT (Quantum Science and Technology) and the Swiss Society for Neutron Science (SGN), leading to an exciting conference, covering latest advancements of physics in a wide range of fields at its best.
Abstract Submission Deadline extended: 17 May 2019
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Registration Deadline extended: 11 August 2019
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Mensa or nearby restaurants
The growth of data from simulations and experiments is expanding beyond a level that is addressable by established scientific methods. The so-called “4 V challenge” of Big Data – Volume (the amount of data), Variety (the heterogeneity of form and meaning of data), Velocity (the rate at which data may change or new data arrive), and Veracity (uncertainty of quality) – is clearly becoming eminent also in the sciences. Controlling our data, in turn, sets the stage for explorations and discoveries. Novel approaches and tools of Artificial Intelligence can find patterns and correlations in data that cannot be obtained from individual calculations or experiments and not even from high-throughput studies. In fact, data-driven research is adding a new research paradigm to the scientific landscape. I will discuss the concepts and recent progress of data-driven materials science, also addressing the importance of FAIR and Open Data.
Planets are common astrophysical objects. Giant planets, which are massive planets made of mostly hydrogen and helium, are the first planets to form in planetary systems, and due to their large masses they affect the dynamical evolution of the system. In addition, giant planets reveal critical information on the planetary birth environment and the formation process.
Gas giants are thought to have cores in their deep interiors, and the division into a heavy-element core and hydrogen-helium envelope is applied in both formation and interior models. I will briefly summarize giant planet formation models, and will show that the primordial internal structure of giant planets depends on their growth history and evolution. I will present current-state internal structure models of Jupiter, and their connection to high-pressure physics. Finally, I will discuss the importance of the recent theoretical results for interpreting the measurements of the Juno mission and for characterizing giant exoplanets.
Mensa or nearby restaurants
Weyl fermions can arise in Weyl semimetals (WSMs) in which the energy bands are usually nondegenerate, resulting from inversion or time-reversal symmetry breaking. Nevertheless, experimental evidence for magnetic WSMs is scarce. Here, using photoemission spectroscopy, we observe the degeneracy of Bloch bands already lifted in the paramagnetic phase of EuCd2As2. We attribute this effect to the itinerant electrons experiencing quasi-static and quasi-long-range ferromagnetic fluctuations. Moreover, the spin-nondegenerate band structure harbors a pair of ideal Weyl nodes near the Ef. Hence, we show that long-range magnetic order and the spontaneous breaking of time-reversal symmetry are not an essential requirement for WSM states in centrosymmetric systems, and that WSM states can emerge in a wider range of condensed-matter systems than previously thought.
Micro-resonators fabricated by optical lithography can be combined with scanning transmission x-ray microscope (STXM) and a time-resolved detection scheme to measure magnetic excitations in ferromagnetic resonance (FMR) with ultimate spatio-temporal resolution of nominally 35 nm and a snapshot detection down to 17.4 ps [1]. Two perpendicular Permalloy micro-stripes were fabricated using e-beam lithography and pre-characterized using conventional FMR. The dynamic magnetic contrast measured by STXM-FMR enable to directly observe both uniform FMR modes as well as inhomogeneous spin-wave modes which exhibit a remarkably good agreement with respective micro-magnetic simulations. Moreover the properties of the spin-waves can be modified via the mutual positioning of the two Py stripes.
[1] T. Schaffers et al., Rev. Sci. Instrum. 88, 093703 (2017)
Spin pumping is an efficient mechanism for the inception of spin current and for its conversion into charge current in non-magnetic metals or semiconductors via spin Hall effects. The generation of spin current in bilayers Py/n-GaN:Si is here reported. In n-GaN:Si and for a layer thickness greater than the spin diffusion length - a condition not met in previous studies on e.g. n-ZnO - a spin Hall angle θSH = 3.03 × 10−3 is found, exceeding by one order of magnitude those of other relevant semiconductors, and pointing at wurtzite nitride compounds as efficient spin current generators.
The field of STM induced light emission (STM-LE), especially on single molecules, has grown rapidly in the past 25 years [2] with astounding spatial as well as energetic resolution [3]. Yet, combining structural and optical information on single molecules remains challenging.
We present first results of a combined AFM and STM-LE setup on single vanadyl-phthalocyanine (VOPc) molecules. This setup so far allows for structure determination with atomic resolution by AFM with CO functionalized tips [5] and the possibility to perform controlled atom manipulation conjunct with the investigation of opto-electronic properties by STM-LE.
[2] X. Qiu et al. (2003). Science, 299(5606), 542–547.
[3] B. Doppagne et al. (2017). Phys. Rev. Lett., 118(12), 127401.
[5] Gross et al. (2009). Science, 325(5944), 1110–1114.
In this talk I present a new ab-initio theory for superconducting systems with non-local external potentials based on the one-particle reduced density matrix ρ(r,r′) and the anomalous density χ(r,r′). All the equilibrium properties of the system are determined uniquely by these two quantities. By replacing the local electronic density with the non-local one-particle reduced density matrix, our theory is able to solve difficulties which arise in DFT for superconductors. I sketch the proof of the existence of a non-interacting Kohn-Sham system that is able to reproduce ρ and χ of the interacting system at finite temperature. On the basis of the Kohn-Sham system, one obtains a set of Bogoliubov-de Gennes-like single particle equations.
Coulomb phases can be constructed for degrees of freedom that obey an ice rule on the pyrochlore lattice. Using diffuse and single crystal neutron and powder x-ray scattering, we identify a structural Coulomb phase (charge ice) formed by the Ni$^{2+}$ and Cr$^{3+}$ cations in CsNiCrF$_6$. The cations form a configurational structural ice and dictate local distortions of the (Ni/Cr)F$_6$ octahedra, which inherit Coulomb phase correlations. The resulting exchange disorder can be mapped to a fully-packed loop model. Despite this disorder, diffuse and inelastic magnetic neutron scattering show that the spins also form a Coulomb phase, whose correlations and dynamics have much in common with those of the canonical pyrochlore Heisenberg antiferromagnet.
T. Fennell et al., Nat. Phys. 19, 60 (2019)
Semiconductor-Metal heterostructures act as energy filters for charge transport with promising applications in thermoelectric energy conversion. Using a scanning thermal microscope technique we measure the temperature distribution of operando Al-Ge-Al nanowire devices integrated in a back-gated field effect transistor. The Ge segments are contacted with self-aligned quasi one-dimensional crystalline Al leads of 20 nm diameter. The high spatial resolution of our temperature map allows for the extraction of parameters governing the thermoelectric processes at the energy barrier, which are hardly extractable using other techniques. We extract Peltier coefficient, thermal conductivity and interface resistance to the substrate.
The frustrated nearest-neighbour antiferromagnetic Ising model on the kagome lattice exhibits a macroscopic ground state degeneracy. We implement an MCMC algorithm to study the degeneracy lifting leading to the ground state of the dipolar model, focusing on models with up to fourth neighbour interactions.
The ground state of the J1-J2-J3 model exhibits five different phases as a function of the ratio J3/J2, four of which still have a non-zero residual entropy. We investigate how tensor networks can help to better understand these phases.
Surprisingly, in the model with dipolar couplings truncated at fourth neighbours, we find states lower in energy than the ground states of the dipolar J1-J2-J3 model and the full dipolar model: further neighbours must play a role.
The quantum magnet BaCuSi2O6, consisting of stacked spin dimer bilayers, undergoes an anomalous dimensional reduction from 3D to 2D close to the quantum critical point [1]. Mechanisms for this dimensional reduction were proposed based on inter-bilayer frustration resulting from an antiferromagnetic intra-bilayer exchange. Ab initio calculations propose a ferromagnetic intra-bilayer exchange rendering such a frustration impossible [2]. We have performed neutron spectroscopy on BaCuSi2O6 and Ba0.9Sr0.1CuSi2O6. Our results suggest ferromagnetic intra-bilayer exchanges with at least three different dimer types in BaCuSi2O6 and only one dimer type in Ba0.9Sr0.1CuSi2O2. We conclude that the existence of different dimer types in BaCuSi2O6 might lead to the observed 2D behavior.
[1]C.E.Sebastian et al., Nature 441, 617 (2006).
[2]V.V.Mazurenko et al., PRL 112, 107202 (2014).
Using the Matrix Product State framework, we generalize the Affleck-Kennedy-Lieb-Tasaki (AKLT) construction to one-dimensional spin liquids with global color ${\rm SU}(N)$ symmetry, finite correlation lengths, and edge states that can belong to any self-conjugate irreducible representation of ${\rm SU}(N)$. Families of local parent Hamiltonians can be constructed and allow us to study the stability of the edge states by interpolating between exact AKLT points. In particular we show that the topologically trivial phase of a spin-$1$ chain with spin-$1$ edge states can be reached from the original AKLT point through a continuous phase transition described by the $\rm{SU}(2)_1$ WZW conformal field theory.
We investigate the topology of a periodically-driven two-dimensional Chern insulator hosting anomalous edge modes. Using a renormalization group approach on the stroboscopic Berry curvature, we obtain flow diagrams that clearly delineate all topological phase boundaries, therefore demonstrating that a detailed knowledge of the micromotion is not necessary to assess the appearance of the Floquet topological phase transitions. Furthermore, we characterized the critical behavior of the Floquet topological excitation by extracting the critical exponents of measurable diverging quantities. We discover that two di?fferent universality classes coexist in the same model: a class characterized by linear, Dirac-type gap closures and another outlined by quadratic gap closures associated with a low-energy theory described by a nodal-loop semimetal.
Model Hamiltonians with quasicrystalline order display a hierarchy of phenomena at different scales and are excellent starting points to explore unconventional effects not achievable in conventional periodic solids. In this talk, I will present a theoretical study of the model that interpolates between two well-known quasiperiodic examples: Aubry-André and Fibonacci model. In particular, I will show the analysis of the localization properties of this model. We find that by controllably evolving an Aubry-André into a Fibonacci model, a series of localization-delocalization transitions take? place before the spectrum becomes critical. Our findings provide new insights about the forming of criticality in quasiperiodic systems and open up new avenues to study the interplay among quasiperiodicity, topology, and interactions.
Topological insulators are a novel state of matter which, to date, have seen a variety of manifestations. All available realizations, however, share a common feature: their spectral bands are attributed with a nonlocal index that is quantized. This unique topological property commonly manifests through exotic bulk phenomena and robust boundary effects. In this talk, I will present a foundamental 4D insulator and show the connection of the 2nd Chern number to the 0-dimensional localised states found in 2-dimensional 2nd-order TIs.
I will present our theoretical work that aims at revealing systematic trends and developing intuition across the entire family of 2D transition metal dichalcogenides (TMDs). I will address the relevance of the crystal and ligand fields in determining the relative stability of 1T and 1H polymorphs and introduce a unified picture of lattice instabilities (charge-density-wave and strong-coupling regime) in metallic TMDs. The rest of my talk will focus on two particular realisations of topological and magnetic phases. I will discuss the well-ordered 1T’-1H heterojunctions experimentally observed in WSe$_2$ in relation to the quantum spin Hall interface states and present the observation of magnetic ordering and magnetoresistive switching in few-layer PtSe$_2$ that realises a new scenario in magnetic 2D materials.
Topological quantum materials have become a ubiquitous topic in condensed matter physics over the past decade, but there is still plenty of room for new discoveries of exotic topological phases and improvements in device engineering. Here, I will report our achievements in thin film growth, soft X-ray angle-resolved photoemission spectroscopy (SX-ARPES), and scanning tunnelling microscopy and spectroscopy (STM and STS), to synthesize new materials and characterize and engineer their electronic properties, such as:
1. Tuning of the band offset at superconductor/semiconductor interfaces for applications in Majorana zero mode heterostructures.
2. Investigation of the interplay between chirality and Fermi-arc topography in chiral topological semimetals.
3. Synthesis and spectroscopy of a novel two-dimensional material with flat bands.
Using muon spin-rotation experiments and density functional theory calculations, we present evidence for competing magnetic orders in a topological kagome magnet Co$_3$Sn$_2$S$_2$ [1]. Our results show that while the sample exhibits an out-of-plane ferromagnetic ground state, an in-plane antiferromagnetic state appears at temperatures above 90 K. Strikingly, the reduction of the anomalous Hall conductivity above 90 K linearly follows the disappearance of the volume fraction of the ferromagnetic state. We further show that the competition of these magnetic phases is tunable through applying either an external magnetic field or hydrostatic pressure. Our results taken together suggest that the magnetic competition drives the thermal and quantum evolution of Berry curvature field in Co$_3$Sn$_2$S$_2$, thus tuning its topological state.
[1]Guguchia et.al., arXiv:1904.09353(2019).
We present our recent results on the local magnetic and electronic properties at the topological insulator/ferromagnetic insulator interface EuS/Bi$_2$Se$_3$, which was previously reported to exhibit magnetic proximity persisting up to room temperature [1]. We use antiresonant ARPES at the Eu $M_5$ pre-edge to access the interface electronic band structure. Low energy muon spin rotation reveals strong local magnetic fields extending several nm into Bi$_2$Se$_3$, below the magnetic transition of EuS. However, we find a very similar result upon replacing Bi$_2$Se$_3$ with titanium, implying that its origin is mostly independent of the topology of the involved layers [2].
[1] F. Katmis, et al., Nature 533, 513 (2016).
[2] J. A. Krieger, et al., Phys. Rev. B 99, 064423 (2019)
In the spin-chain compound CuGeO3, the relation between charge, spin, and lattice degrees of freedom, giving rise to the Spin-Peierls transition, is still unclear. In this system, Resonant Inelastic X-ray Scattering (RIXS) at the O K-edge is capable of detecting charge-transfer excitations, including the formation of a Zhang-Rice singlet. The probability for such a non-local process depends on the magnetic correlations between two neighboring CuO4 plaquettes. We use an ultrashort laser pump to excite carriers across the charge transfer gap, perturbing the local spin correlations by removing magnetic holes from the Cu site. With ultrafast O K-edge RIXS, we probe the suppression and recovery of the Zhang-Rice singlet, giving insight into the dynamics of the short-range magnetic correlations.
An ongoing experiment at PSI aims to determine the nuclear charge radius of $^{226}$Ra - needed by an experiment aiming at measuring atomic parity violation in a radium ion - by means of muonic atom spectroscopy. An intermediate test was performed with a $^{185,187}$Re target which is the last stable element whose nuclear charge radius has not been measured and shows similar nuclear structure effects as radium. In $^{185,187}$Re there exists an intermediate domain of energy states in which the quadrupole splitting is proportional to the spectroscopic quadrupole moment. In this contribution, the analysis of the $5g\rightarrow 4f$ hyperfine transitions in muonic $^{185,187}$Re for the extraction of its spectroscopic quadrupole moment is presented.
The measurement of the hyperfine splitting (HFS) in muonic hydrogen at the ppm level by means of pulsed laser spectroscopy allows for extraction of the Zemach radius of the proton at the per mille level. This measurement, ongoing at the Paul Scherrer Institute, features a novel laser system to excite the HFS transition at 6.8 µm. To increase the transition probability, we will use a multi-pass optical cavity, which enhances the average light fluence on the muonic atoms. In this talk, we will present the principle of the experiment, the cavity requirements and the current state of the optical design. Work supported by SNF project 200021_165854 and ERC CoG. #725039.
Muonic hydrogen is a bound-state of a negative muon and a proton. Since a muon is 207 times heavier than an electron, the energy levels of muonic hydrogen are very sensitive to the nuclear structure. By means of laser spectroscopy, we are aiming at the measurement of the ground-state hyperfine splitting to extract the two-photon exchange contribution and the Zemach radius of the proton. This experiment is being conducted at Paul Scherrer Institute and it requires designing a detector system capable of measuring the MeV-energy X-rays produced by the muonic atoms. In this talk we will introduce the simulations and the initial laboratory tests of the detection system. Work supported by SNF project 200021_165854 and ERC CoG. #725039.
The magnetic (Zemach) radius of the proton can be determined from the ground-state hyperfine splitting (HFS) of muonic hydrogen (bound state between muon and proton). At PSI, Switzerland, we aim to measure this HFS at the ppm level by means of laser spectroscopy.
Since a high laser fluence at an unusual wavelength (6.8 micrometer) is required to excite the HFS, a novel laser system will be developed. Its back bone is a thin-disk laser insensitive to thermal lens effects, delivering single-frequency pulses at 1030 nm with hundreds of mJ which will be converted to 6.8 micrometer via non-linear conversion stages. We will present results related to the thin-disk laser development.
Work supported by SNF project 200021_165854 and ERC CoG. #725039.
The ASACUSA collaboration, based at the AD of CERN aims to measure the ground state hyperfine structure of antihydrogen at a ppm level relative precision with a Rabi-type beam experiment [1]. For the same, a spectrometer line has been fully commissioned with studies on hydrogen, with a relative precision of 10$^{-9}$ [3]. This precision can be pushed further by the Ramsey method. Using the existing stripline cavity, the decisive Ramsey fringes near the transition frequency can’t be observed, thus demanding the finite element simulations and design of various options for new cavity and transmission lines, which shall be discussed.
[1] A. Mohri and Y. Yamazaki, Europhys. Lett. 63, 207–213 (2003).
[2] M. Diermaier et al., Nat. Commun. 8, 15749 (2017)
Recently, we have performed measurements on vacuum muonium formation at room and cryogenic temperatures at the the Paul Scherrer Institute. These measurements were conducted in the context of our efforts on the investigation of the gravitational interaction of antimatter and second-generation particles.
In our room temperature setup, the muon beam impinged on several targets such as zeolite powder, ablated aerogel and semiconductor carbon-nanotubes. The relative yield and velocity of the observed vacuum muonium are presented. At cryogenic temperature, the targets were dry and superfluid-helium coated aerogel. While vacuum muonium was not observed directly in this case, we did observe the formation of muonium by means of the spin rotation technique. This contribution will present and compare.
The neutron's electric dipole moment is a probe sensitive to a broad range of CP violating physics beyond the standard model. However, a nonzero measurement remains elusive, despite successive measurements performed worldwide since 1951 improving in sensitivity by over 6 orders of magnitude. The most recent measurement took data from 2015-2016 at the ultracold neutron source at the Paul Scherrer Institute, and is set to publish in the coming months the first improvement since 2006 in the sensitivity of this measurement. I will present the experiment, the data analysis methodology and progress towards the publication of the new result.
The author gratefully acknowledges support from the SNF via grant no. 200020-172639.
The n2EDM experiment hosted at the Paul Scherer Institute is seeking an improvement in the measurement of the neutron electric dipole moment (nEDM) by one order of magnitude. In order to achieve this goal, it is crucial to stabilize the magnetic fields inside the precession chamber, where neutrons are stored and Ramsey measurements are performed, down to 30 fT. This is especially challenging considering that the surrounding magnetic fields undergo substantial changes due to the activity of neighboring experiments. Therefore, an active magnetic shielding, which compensates the surrounding field and the occurring field changes via a feedback loop, is indispensable. We present how our compensation system design can meet the high performance goal despite various challenges, such as spatial constraints.
The search for the neutron electric dipole moment $d_n$, carried on by the n2EDM experiment at PSI could provide a better insight on the baryon asymmetry of the universe and/or new physics. The experimental goal to reach an order of magnitude higher sensitivity than previous efforts, means its systematic effects need to be better controlled. The appearance of a false $d_n$ ($d^{false}_{Hg\rightarrow n}$) due to the different motional magnetic fields seen by the neutrons and Hg atoms of the comagnetometer is one of such obstacles. This study aims at developing and building a Cs-Magnetometer array to measure the magnetic field in the experiment with high-enough precision and accuracy to control the associated systematic uncertainty with $d^{false}_{Hg\rightarrow n}\leq 4 \times 10^{-28}e\textrm{cm}$.
The n2EDM experiment being mounted at the Paul Scherrer Institute (PSI) will search for the neutron electric dipole moment (nEDM) with a baseline sensitivity of $1.1 \times 10^{-27} \mathit{e} \cdot \mathrm{cm}$. With the increase in statistical sensitivity, an accordingly better control of systematic effects is required. This study investigates the impact of Johnson-Nyquist noise originating from thermal agitations of electrons in the electric conducting materials in the apparatus. The presentation covers the concepts and methods used to calculate the magnetic noise and shows preliminary results discussing the possible impacts on the measurement sensitivity.
(This project is supported by SNF #200021_169596.)
nEDM project: https://www.psi.ch/en/nedm
A useful quantum computer will require quantum-error-correction, which implies a huge increase in resources over systems in laboratories today. In this context, I will describe work towards scaling up trapped-ion quantum computing, including the use of integrated optics, ion shuttling, and attempts to meet the challenges of calibrating and stabilizing larger scale devices. These core elements should facilitate the exploration of error-correcting codes.
Future quantum networks offer a route to quantum-secure communication, distributed quantum computing, and quantum-enhanced sensing. The applications of a given network will depend on the capabilities available at its nodes, which may be as simple as quantum-state generation and measurement or as advanced as universal quantum computing. Here, we focus on quantum nodes based on trapped ions, an experimental platform with which high-fidelity state preparation, gate operations, and readout have been demonstrated. By coupling trapped ions to the mode of an optical resonator, we construct a coherent interface between single ions and single photons. I will present ongoing work to transfer quantum states between remote trapped-ion systems, highlighting experimental challenges and addressing the question of how to optimize this process.
Quantum simulation enables studying the dynamics of quantum many-body systems in regimes which are inaccessible to numerical methods. With universal digital quantum simulators, time evolution generated by a large class of Hamiltonians can be simulated by approximating the unitary time-evolution operator by a sequence of quantum gates. However, this "Trotterization" introduces an intrinsic source of errors. Our work connects Trotter errors in digital quantum simulation of collective spin systems to quantum chaos of the kicked top: Trotter errors remain bounded in the regime of small Trotter steps, which corresponds to regular motion of the kicked top. Instead, quantum chaos, which sets in above a sharp threshold value of the Trotter step size, leads to the proliferation of Trotter errors.
In quantum systems composed of at least two subsystems, entanglement induces correlations between the properties of the subsystems that cannot be reproduced in classical physics. These strong correlations are used as a resource for many innovative applications of Quantum Physics, such as quantum computation and quantum communication.
One operationally meaningful way to characterise this resource is to study the transformations of entangled states that can be achieved using Local Operations assisted with Classical Communication (LOCC). Although it is known that an entangled state can rarely be converted into another one using only LOCC, we show in this talk that combining the resource of several entangled states allows to achieve more local transformations of entangled states.
Quantum computers allow for a higher level of security in information exchange than their classical counterpart. As an example, by using the so-called blind quantum computing protocols, a client can delegate a complex quantum computation to a server in a completely secure way, without any leaks of information on the input, the output or the computation algorithm. In this work, we realize a blind quantum computing between a completely classical client and a single quantum server, where the classical client uses an ambiguity in the information flow in measurement-based quantum computing to hide the computation algorithm. Our demonstration represents a step toward real-life applications of blind quantum computing, where classical clients delegate computation tasks to a single photonic quantum server.
Quantum communication is one of the most advanced areas of quantum science and technology. It spans commercial devices and systems already deployed to future concepts of a quantum internet. We introduce some of the underlying concepts and targeted applications in this rapidly expanding and advancing field. We start with the simple concept of quantum random number generation and their distribution for cryptographic applications. We then discuss next-generation schemes for the distribution of entanglement, teleportation, and the development of complex communication networks.
Topological materials have many interesting properties and are the focus of intense theoretical and experimental research. The material PrAlGe has recently been predicted to be a Weyl semimetal with broken time reversal and inversion symmetries [1]. We present experimental results on various properties of PrAlGe single crystals such as magnetization, neutron diffraction, and electrical transport with a focus on the origin of the anomalous Hall and Nernst effects. This data is compared to theoretical calculations involving the Berry curvature of the Weyl nodes in the system.
[1] Guoqing Chang et al., Phys. Rev. B 97, 041104(R) (2018)
1T’-MoTe2 is a layered, van der Waals material, which has recently been proposed to host Weyl fermions, linked to the tilted Dirac cones in its band structure. In this transition metal dichalcogenide, very fine energy scales play an important role. However, the precise low-energy structure of these bands has so far been experimentally elusive, due to a complex coexistence of several electronic bands at the Fermi level.
We address the electrodynamics in MoTe2 by exploring its temperature-dependent infrared properties. We identify two pronounced low-lying interband excitations, one of whom strongly shifts with temperature. Using a simple theoretical approach, we can discern the characteristics of the bands crossing the Fermi level, helping to demystify the band structure of 1T’-MoTe2.
Fe3Sn2 is predicted to be a type-II Weyl semimetal which orders ferromagnetically below TC= 646 K. It undergoes a spin reorientation transition (SRT) between 300 K-100 K which together with recently shown coupling between its easy axis and the band structure paves the way of external control of its bulk properties. By probing anisotropic magnetoresistance, bulk magnetization and imaging the domain structure of Fe3Sn2 using XMCD-PEEM at different temperatures, we understand its domain structure together with evolution of easy axis during the SRT. We are able to clearly establish the nature of the SRT to be of first order.
Ref:
1. M. Yao et al. Switchable Weyl nodes in topological Kagome ferromagnet Fe3Sn2, arXiv 1810.01514 (2018).
The low-energy electronic structure and topological nature of ZrTe$_5$ has recently been under debate with several contradictory results published. It consists of nearly linearly dispersing bands at the Gamma point with potentially a small band gap, making ZrTe$_5$ very sensitive to structural defects. However, only minor attention has been given to the influence of the sample growth method on the crystal quality and its physical properties.
Here we present angle-resolved photoemission spectroscopy and scanning tunneling microscopy measurements performed on samples grown by the two different methods used for ZrTe$_5$ growth. We will focus on the presence of defects and discuss their influence on the low-energy electronic structure of ZrTe$_5$.
We investigate two-dimensional spinful bulk insulating phases of matter that are protected by time-reversal and crystalline symmetries. In order to characterize these systems, we use the concept of corner charge fractionalization and show that charges are both quantized and remain stable as long as all symmetries are preserved. To define the topology, we employ symmetry indicators and Wilson loop invariants. We illustrate our results using the example of arsenic and antimony monolayers. Depending on the degree of structural buckling these materials can exhibit two distinct obstructed atomic limits. We present tight-binding and density functional theory calculations for open flakes to support our findings.
Despite being predicted more than a decade ago, Hopf insulators still have no realistic candidate material realization. The problem with finding such material is two-fold: Most importantly, the corresponding topological invariant - integer-valued Hopf number - is only defined for a two-band system, while another source of the problem stems from the assumed absence of any symmetry required to protect the Hopf phase. Apart from that, it is also not clear which properties of a Hopf insulator can be measured in order to find candidate compounds from the physical response. In this work, we address these problems and discuss physical aspects that should allow for the search of the Hopf insulator compounds.
A large-gap Quantum Spin Hall Insulating state was recently predicted to appear in the compound Pt2HgSe3. The lack of knowledge of phase equilibria in the Hg-Pt-Se system as well as the high-volatility and toxicity of the components render the conventional crystal growth methods unusable. Here we report on the successful growth of Pt2HgSe3 crystals at high pressure (1-3GPa), using a cubic anvil isostatic press operating at high temperature (800-1000°C). The largest crystals (~0.9 x 0.5 mm2 in the ab-plane) were grown at 1.5GPa and 900°C, starting from a slightly Hg-rich composition. The crystals exhibit the expected structure and exfoliate in the ab-plane. The successful growth of jacutingaite crystals opens a new perspective towards robust non-trivial 2D topologic materials.
Monolayer jacutingaite (Pt$_2$HgSe$_3$) was recently predicted to be a Kane-Mele Quantum Spin Hall insulator (QSHI), with a topological gap as large as 0.5 eV. We investigated the electronic band structure of bulk single crystals by angle-resolved photoemission. Surprisingly, on the (001) surface, we observed surface states dispersing over large areas of the Brillouin zone, which is unexpected from a 3D stack of 2D QSHI. Using a minimal description that extends the Kane-Mele model to 3D, we demonstrate that these states are topologically protected indicating that bulk Pt$_2$HgSe$_3$ realizes a new form of topological (quantum band) semimetal.
Precision experiments in free neutron beta decay allow probing for physics beyond the Standard Model in a complementary manner to searches conducted at the LHC. NoMoS, the neutron decay products momentum spectrometer, aims to measure the momentum spectra of the charged decay products (electron and proton) in neutron beta decay with high precision. The spectrometer utilizes the concept of an R x B drift of a charged particle in a uniformly curved magnetic field to map its momentum to a drift distance. In this talk, a status update alongside the measurement and detection principles of the experiment will be presented.
The SIDDHARTA-2 experiment aims to observe the energy shift and width of the kaonic deuterium ground state induced by the strong interaction via X-ray spectroscopy.
This measurement requires an improvement of the signal-to-noise ratio of at least a factor of ten compared to SIDDHARTA due to the very low kaonic deuterium X-ray yield. Therefore, three updates to the apparatus are implemented: a lightweight, cryogenic target cell, a large-area X-ray detection system consisting of Silicon Drift Detectors, and a dedicated veto system to suppress signal-correlated background. The characterisation of these updates will be discussed.
Given the lack of smoking gun signatures that point to an energy scale to be explored, the landscape of post LHC Run2 motivates searching for new physics in a region that has not been well covered so far, i.e. physics involving new interactions much weaker than the electroweak scale.
Beam dump facilities of high intensity electron and proton beams can probe an unexplored parameter space of couplings and masses for a wide range of SM extensions, empowering a diverse physics program that covers searches for DM, HS, Axions and Flavour physics. This talk will review the experimental perspectives for beam dump searches, with a focus on the CERN Beam Dump Facility and on SHiP, the first zero-background proton dump experiment.
Cosmological and astrophysical observations point to the fact that the Standard Model (SM) of particle physics account for less than $5\%$ of the total energy density of our Universe. What remains is defined as dark energy and dark matter (DM). More specifically, indirect gravitational interactions measurements indicate that DM is five times more abundant than ordinary baryonic matter.
The existence of DM does not directly point to a specific mass scale for New Physics (NP), conversely a dark sector of particles not interacting through the known SM forces might exist. These new dark particles could communicate to the SM through so-called "portals".
This talk will cover dark sectors future and present experimental searches with a specific focus on high-intensity colliders.
Heavy neutrinos are predicted by numerous Beyond the Standard Model theories that provide answers to long-standing questions, such as the smallness of neutrino masses, matter-antimatter asymmetry and the nature of dark matter. In this talk, a status report on a search for a long-lived heavy neutrino decaying to three leptons is presented. This analysis focuses on the final state with one displaced lepton pair and uses the resulting invariant mass to look for an excess between 1 and 10 GeV. Data-driven methods are developed to model misidentified and non-prompt lepton backgrounds in the signal region. A sample of 41.53 $fb^{-1}$ of proton-proton collision data collected with the CMS detector in 2017 at $\sqrt s = 13$ TeV is used.
NA64 is a fixed target experiment at the CERN SPS aiming at a sensitive search for hidden sectors. The A′, called dark photon, could be generated in the reaction e−Z→e−ZA′ of 100 GeV electrons dumped against an active target which is followed by the prompt invisible decay A′→χχ. The experimental signature of this process would be a clean event with an isolated electron and large missing energy in the detector. Results on the search for the visible A' -> e+e− decays, as well as X→ e+e− decay of a new 17 MeV X boson, which could explain a recently observed anomaly in the 8Be transitions will be also discussed.
The Belle II experiment at the SuperKEKB collider of KEK (Japan) will accumulate 50 ab$^{−1}$ of $e^+e^−$ collision data at an unprecedented instantaneous luminosity of $8\cdot 10^{35}$ cm$^{−2}$s$^{−1}$, about 40 times larger than its predecessor. The Belle II vertex detector plays a crucial role in the rich Belle II physics program, especially for time-dependent measurements. It consists of two layers of DEPFET-based pixels and four layers of double sided silicon strip detectors (SVD). The vertex detector has been recently completed and installed in Belle II for the physics run started in spring 2019. In this presentation, we summarise the construction and installation of SVD and report first results from SVD commissioning and SVD performance in the first SuperKEKB collisions.
The LHCb experiment obtained outstanding results with the data collected during last two LHC data taking periods.
An upgrade of the LHCb detector will be installed aiming for a full detector readout at 40 MHz for Run 3 and 4. To cope with the increased luminosity, the current downstream tracking system will be replaced by the the Scintillating Fibre tracker.
The SciFi tracker uses 250µm scintillating fibres densely packed and arranged in layers readout by Silicon Photo-Multipliers (SiPMs).
Each single detector has to be characterised in terms of its electrical, geometrical and optical properties. A testing facility to characterise the 5500 multichannel arrays has been developed and employed during the production testing.
At the end of the Run 2 of the LHC the current Inner Detector (ID) of the ATLAS experiment will need to be replaced. A new all-silicon Inner Tracker (ITk) is currently being designed and given the increase in the simultaneous p-p collisions, its data-taking system will have to use radiation hard high-speed data links at 10 Gbps, for a total bandwidth of ~ 60 Tbps. In this talk, the concept of the data transmission chain as well as its validation will be presented. The integration with the FELIX backend readout will be shown as well with results from a system where this readout is coupled to an existing set of silicon pixel readout chips.
For operation at the High Luminosity LHC, the ATLAS detector will be upgraded in 2024-2026. Its Inner Tracker will be able to handle pile-up conditions of $\mu = 200$ which increases the digital data output significantly. A new optical to electrical conversion stage, the Optoboard system, needs to be designed in order to cope with this higher bandwidth requirement. In this talk I present the first prototype component development for the Optolink system with regards to powering and the cooling control. Results from measurement on full opto-system prototypes are also presented.
A serially powered pixel detector is the baseline choice for the High-Luminosity upgrade of the inner tracker of the CMS experiment. A serial power distribution scheme requires less cable mass, improves power efficiency and is less susceptible to voltage transients than parallel powering. A prototype pixel-readout-chip has been designed for serial powering in 65nm-CMOS technology by the RD53 collaboration. Performance results from testing the prototype,called RD53A, are reported. The performance of RD53A operating in a chain consisting of four serially powered chips is compared with the performance under a conventional powering scheme. Additionally, the readout efficiency of RD53A in a high hit rate environment is presented. The results indicate that serial powering is a robust and reliable power distribution scheme.
Statistical modelling is a key element for High-Energy Physics (HEP) analysis. Currently, most of this modelling is performed with the ROOT/RooFit toolkit which is written in C++ and poorly integrated with the scientific Python ecosystem. We present zfit, a new alternative to RooFit, written in pure Python. Built on top of TensorFlow (a modern, high level computing library for massive computations), zfit provides a high level interface for advanced model building and fitting. It is also designed to be extendable in a very simple way, allowing the usage of cutting-edge developments from the scientific Python ecosystem in a transparent way.
This presentation introduces the main features of zfit and its extension to data analyses in the context of HEP experiments.
The ArgonCube Collaboration developed a novel design for Liquid Argon Time Projection Chambers (LAr TPCs), segmenting the total detector volume into a number of electrically and optically isolated TPCs sharing a common cryostat. For the charge-readout, a pixelated anode plane is employed, providing unambiguous 3D event reconstruction. To minimize inactive and dense material a new technology is used for field-shaping, replacing the classical field-cage by a continuous resistive foil. Large dielectric planes inside the field-shaping structure allow for an efficient detection of prompt scintillation light. The technology proposed by ArgonCube will be applied to the near-detector of the Deep Underground Neutrino Experiment, DUNE, and being proposed also for one of the far-detectors.
As part of the R&D towards the ultimate dark matter observatory DARWIN, we conduct tests with novel silicon photomultipliers (SiPM) for vacuum ultra violet (VUV) light being a promising alternative to traditionally used photomultiplier tubes. In particular, we are operating a small-scale dual phase (liquid/gas) xenon time projection chamber (TPC) instrumented with VUV-sensitive SiPMs from Hamamatsu for light and charge readout, being the first in the field. After a successful commissioning in Summer 2018, in this talk, we present the results from $^{83\mathrm{m}}$Kr calibration data to proof the principle of the detector design with the new photosensors. Moreover, we will show the analysis from a recently performed low-keV energy calibration with $^{37}$Ar gas at the energy threshold of the detector.
Quantum memories are an essential ingredient for quantum repeaters. Further, through synchronization they can facilitate the generation of multiphoton states. This enables scaling optical quantum information processing experiments into a regime beyond the realm of classical simulation. We implemented a broadband optical quantum memory with on-demand storage and retrieval in hot Rb vapor. Operating on the Rb $\text{D}_1$ line, this memory is suited for storing single photons emitted by GaAs droplet quantum dots or by spontaneous parametric down conversion (SPDC) sources. We demonstrate storage of true single photons with a bandwidth of 200 MHz, generated by a SPDC source with 50% heralding efficiency, and show non-classical $g^{(2)}<1$ of the photons read out of the memory.
Quantum memories are key devices for future quantum networks. The atomic frequency comb (AFC) scheme in rare-earth doped crystals provides solid-state memories with many appealing features, such as high efficiency, multimode capacity and long storage times. The previous record storage time achieved in an AFC memory was around 1 ms, in a Europium-doped Y2SiO5 crystal at zero applied magnetic field. Even longer storage should be possible by dynamical decoupling (DD) of the spin states, but efficient DD was so far unsuccessful at zero field due to the double degenerate nuclear states. In our newest work we demonstrate storage of optical pulses for up to half a second using the AFC scheme and DD in a Eu:Y2SiO5 crystal under magnetic field.
Mechanical oscillators have a rich history and role in precision science, ranging from the atomic force microscope, gravitational wave detection to technology such as filters in cell phone or quartz oscillators. The dissipation of the mechanical oscillator plays a key role in setting the thermal decoherence rate, limiting e.g. the ability to observe radiation pressure quantum effects, or placing a limit on force sensitivity. In recent years advances in material strain engineering, phononic band-structure engineering and nanofabrication have allow to create mechanical oscillators with unprecedented coherence. In this talk these advances are reviewed which enable mechanical oscillators with room temperature quality factors as high as 1 billion, sufficient for room temperature ground state cooling of a macroscopic mechanical oscillator.
Quantum simulations open the path for understanding complex quantum matter. Among the large variety of possible approaches, ultracold quantum gases offer a skilful realization of models in condensed matter physics from the weakly to the strongly correlated regime. The key benefits lie on in the ability to reach a high degree of isolation and state control, to change the system’s dimensionality, and to engineer the interaction between particles. So far, the large majority of realized systems employed ultracold atomic species with dominant contact interactions. However, recently highly magnetic species established themselves as novel powerful resources in the quantum realm thanks to their long-range and anisotropic dipole-dipole interaction.
Today, the quest for dipolar quantum simulators marks one of the latest developments in the rapidly evolving field of quantum gases. This talk will present an overview of our latest developments, from the first realizations of quantum-degenerate dipolar gases and mixtures of erbium and dysprosium, to the observation of novel quantum-fluid phenomena such as roton excitation and supersolid phases and the realization of strongly correlated many-body quantum systems of increased complexity. For magnetic atoms confined in light crystals, we will show how the large spin nature of our magnetic atoms and the long-range character the interaction remove the restriction of on-site interaction and allow to process extended Hubbard-type Hamiltonians with extra spin degrees of freedom.
A Bose-Einstein Condensate (BEC) inside an optical resonator can undergo a phase transition to a self-organised state when illuminated with a red-detuned pump beam.
In our recent experiment, we explore the blue-detuned case. We observe that self-organisation is still possible despite the atoms being expelled from the light fields. Moreover, the repulsive lattice modifies the inter-band coupling and the dispersive shift triggers dynamics of the order parameter, both effects leading to richer phase diagrams.
In a second experiment, we study the interaction of the BEC with two non-degenerate polarisation modes of a cavity. I will show how the couplings to the modes - independently tuned via the scalar and vector atomic polarisability - give rise to competing self-organisation phases.
Controlling the internal state of a particle in an ultracold atom experiment is important for studying spinor phases and to simulate spin physics. This control can be implemented using light fields that couples differently to the internal states. This was successfully used in several experiments, although the experiment time is usually constrained by the heating induced by the laser beams.
Here, we create fully spin-polarized currents in an ultracold experiment of fermionic lithium. By shining the spin-dependent, close-to-resonant beam on a small constriction connecting two reservoirs, we demonstrate that the heating is limited: we lift the spin degeneracy for weak interactions while retaining conductance plateaus. This setup can be use to detect small variations of transport thanks to interactions.
Many important chemical and biological processes occur at the interface between a solid and a liquid. Despite its importance, it is very difficult to collect meaningful signals from this buried interface. We recently built a new instrument at the Swiss Light Source that combines ambient-pressure X-ray photoelectron spectroscopy with in-situ electrochemistry. With this new setup, we can stabilize a thin liquid film by a dip&pull method and using tender X-rays, we can probe the solid-liquid interface while having potential control over the electrolyte film. We will present results from the first commissioning beamtime and outline the future direction we are going to pursue.
Cuprous oxide is a promising material for light absorption and charge separation in photoelectrochemical cells for solar water splitting. We have investigated the electron dynamics on the (111) surface of Cu2O. Depending on the defect concentration, this surface shows two different reconstructions. For the (1x1) structure a fast relaxation of a higher conduction band into the conduction band minimum takes place, followed by a slow depopulation of the latter (20ps). For the (√3x√3)R30° surface, the properties change drastically. Comparative studies show that the defect density and band bending play key roles in the dynamics at these surfaces.
Photocatalytic water splitting allows storing solar energy as chemical energy. For large scale application in photoelectrochemical (PEC) cells, electrode materials need to be efficient and stable. In this work we investigate single-crystalline antimony selenide (Sb2Se3), a p-type semiconductor with excellent light absorbing properties and promising stability towards photocorrosion in aqueous environment. We studied cleaved Sb2Se3 surfaces with respect to their structural and electronic properties by means of XPS, XPD, LEED, STM and ARPES. The samples cleave along the (100) planes and the surface shows a pronounced one-dimensional structure, reflecting the zig-zag stacking of ribbons in the bulk crystal structure.
The hexagonal boron nitride (h-BN) nanomesh that forms on Rh(111) has a corrugated honeycomb structure with 3.2 nm periodicity, which consists of “pore” and “wire” regions [1, 2]. In the present study, we demonstrate that 2 nm voids can be fabricated at the pore sites in the h-BN monolayer with unique two-step process in vacuum [3, 4], and can be further delaminated from a Rh substrate with electrochemical method onto arbitrary substrates outside of vacuum as nanoporous membranes [5]. Results from photoemission, scanning tunneling microscopy and density functional theory will be reported.
The growth of hexagonal Boron Nitride (h-BN) monolayers on Pt(110) was investigated by STM, LEED and DFT calculations. Borazine exposure at T < 1100 K yields an h-BN film with defects and domain boundaries on a rough Pt surface as previously reported by Achilli et al. [Nanotechnology 29 (2018) 485201]. Deposition at T > 1100 K results in a perfect single-domain h-BN layer on a flat Pt(110) surface. The lattice misfit is accommodated by converting the (1x2)-missing-row (mr) of clean Pt(110) into a (1xn)-mr reconstruction (n = 5 or 6). This is a rare case of epitaxial growth on a “quasi-liquid” surface where the substrate responds to the adlayer geometry rather than the other way round.
On- surface synthesis enables fabrication of graphene nanoribbons (GNRs) with atomically precise edges and ribbon width which allows tuning their electronic bandgap. This feature makes GNRs interesting candidates for application in room temperature switching devices like field effect transistors (FETs). However, integrating GNRs as the active material in FETs poses great challenges concerning contact area and yield. This contribution addresses some of the critical challenges in the further development of GNR technologies, in particular on GNR fabrication, substrate transfer and GNR characterization.
PdGa(111) surface is of remarkable interest because of its enantio- and region-selective properties. In this work we present experimental and theoretical results concerning the PdGa-catalysed Huisgen cycloaddition (in the Figure, experimental STM images of reactants and products on PdGa(111)), with particular focus on the DFT modelling of the compounds. The calculations were performed treating exchange and correlation as well as van der Waals forc-es with increasing levels of accuracy. Thanks to this technique, we identified the origin of the extremely high enan-tiomeric excess observed, together with the most favourable adsorption sites. Eventually, the source of the regi-oselectivity is analysed and the role of possible modifications of the substrate is discussed.
Since the mid-nineties of the 20th century, it became apparent that one of the centuries’ most important technological inventions, computers in general and many of their applications could possibly be further enhanced by using operations based on quantum physics. Computations, whether they happen in our heads or with any computational device, always rely on real physical devices and processes. Data input, data representation in a memory, data manipulation using algorithms and finally, data output require physical realizations with devices and practical procedures. Building a quantum computer then requires the implementation of quantum bits (qubits) as storage sites for quantum information, quantum registers and quantum gates for data handling and processing as well as the development of quantum algorithms.
In this talk, the basic functional principle of a quantum computer will be reviewed. It will be shown how strings of trapped ions can be used to build a quantum information processor and how basic computations can be performed using quantum techniques. The quantum way of doing computations will be illustrated with analog and digital quantum simulations. Ways towards scaling the ion-trap quantum processor will be discussed.
For decades miniaturization has been the driving force behind semiconductor technology and the enabler of today's information technology. The development of smaller devices resulting in faster chips and consequently cheaper microprocessors drove this first-of-a-kind revolution in IT.
Today, the fundamental question raised is: what is next? What will the next revolution be?
With the explosion of available data, the internet-of-things and the increasing demand for machine learning, deep learning and artificial intelligence, the computational workloads are significantly changing. Therefore, there is a growing need for specialized hardware that can handle large computational workloads that take too long to run on conventional machines. In that regard completely new computing paradigms are being developed, such as quantum computing and non-von Neumann computing.
I will give an overview of our research activities in the field of these new paradigms of cognitive hardware technologies and quantum computing.
Continuous progress in observation and theory allows to study sources of Cosmic Rays in our Galaxy in ever increasing numbers, variety and phenomenological complexity. We are presently witnessing a broadening of the research field from individual source studies to investigations of population aspects, as well as seeing Galactic source physics reaching out into the extragalactic domain. Some source classes do not permit straight generalization owing to their uniqueness (Galactic Center), or their evidently complex class composition (gamma-ray binaries). I will review properties and phenomenology of Galactic sources in the interplay between observations and assumptions regarding their primary and secondary particles, with the focus of key results from recent Cosmic Ray charged particle and nuclei measurement and source taxonomy at the energetic gamma-ray sky.
Quantum mechanics gives a bound on how precisely two non-commuting observables can be predicted, as expressed by the Heisenberg uncertainty principle. Nevertheless, Einstein, Podolsky and Rosen (EPR) realised that there are situations in which measurements on one system allow to predict measurement results on an other system with certainty, seemingly violating the uncertainty relation.
By performing experiments with ultracold atomic ensembles, we have been able to observe for the first time this EPR “paradox” between two many-body systems. Apart from their fundamental interest, our investigations could find application in quantum metrology, for example to sense gradients.
During this presentation, our studies on entanglement and Bell correlations will also be mentioned.
The route of a physical system toward equilibrium and thermalization has been the subject of discussion since the time of Boltzmann. In this talk I review the recent progress in understanding many-body localization (MBL), a phase of matter in which quantum mechanics and disorder conspire to prohibit thermalization altogether. I discuss the current understanding of the novel quantum-to-classical transition between MBL and ergodic phases, for which the analytically solvable renormalization group suggests a Kosterlitz-Thouless universality class. I conclude by discussing experimental challenges and open questions related to the thermalization breakdown in quantum systems.
Mensa or nearby restaurants
Complex oxide thin films and heterostructures exhibit a wide variety of interesting functionalities at their interfaces, which are often not present in the corresponding bulk components. Here, we report on a metallic interface in multilayers of two Mott insulators, LaVO3 and LaTiO3, using a combination of density functional theory (DFT) and dynamical mean-field theory (DMFT). We show that the metallic layer results from charge transfer across the interface, which can be understood in terms of the electronegativity difference of the bulk materials. We demonstrate how expitaxial strain can be used to control the spatial extension of this layer, with tensile strain leading to a localization within a thickness of only two unit cells.
Interplay between spin, charge, orbital and lattice degrees of freedom is extremely strong and at the origin of numerous phenomena in complex oxides [1]. The bulk 3d2 LaVO3 showcases an interesting phase diagram where the low temperature orbital and spin ordering are strongly dependent upon the A cations size [2]. The GdFeO3-type distortions remove the t2g degeneracy and modify the bandwidth to generate a Mott state. Above the transition temperature (140 K), LaVO3 is a paramagnetic insulator while below, an orbital and spin order establishes [3]. The transition can be described mainly by one-dimensional orbital correlations between dxz and dyz states since the lowest energy dxy orbitals have an occupation number close to one. We have explored different effects of biaxial strain in epitaxial thin films of LaVO3. X-ray diffraction reveals that the layers accommodate the strain imposed by the substrate assuming different patterns of octahedral tilts and rotations. We used temperature dependent X-ray diffraction, muon spectroscopy and optical conductivity to investigate how the strain-induced crystal field splitting [4] alters the d-d orbital correlations.
[1] D. I. Khomskii, Transition metal compounds (Cambridge University Press, 2014).
[2] Y. Ren et al., Nature (London) 396, 441 (1998); Phys. Rev.B 67, 014107 (2003).
[3] M. De Raychaudhury, E. Pavarini, and O. Andersen,Phys. Rev. Lett. 99, 126402 (2007).
[4] G. Sclauzero, K. Dymkowski, and C. Ederer, Phys. Rev. B 94, 245109 (2016).
Thin films of the transition-metal oxide LaNiO$_3$ (LNO) undergo a metal-insulator transition when their thickness is reduced to 2-3 unit cells. Here, we use a state-of-the-art laser-ARPES setup to map the electronic structure of LNO thin films with improved resolution. A series of high-quality films of thicknesses ranging from 19 to 2 unit cells is grown by sputter deposition and transferred in vacuo to the ARPES setup. Our measurements show an unchanged Fermi surface for all metallic samples. However, the peak width of the momentum distribution curve at the Fermi level progressively increases as the thickness is reduced. This suggests that the metal-insulator transition is driven by the increasing importance of interfacial scattering and a reduced inelastic mean free path.
Probing the local transport properties of two-dimensional electron systems (2DES) confined at buried interfaces requires a non-invasive technique with a high spatial resolution operating in a broad temperature range. In this paper, we investigate the scattering-type scanning near field optical microscopy as a tool for studying the conducting LaAlO$_3$/SrTiO$_3$ interface from room temperature down to 6K. We show that the near-field optical signal, in particular its phase component, is highly sensitive to the transport properties of the electron system present at the interface. Our model allows to quantitatively correlate changes in the optical signal with the variation of the 2DES transport properties induced by cooling and by electrostatic gating. Imaging conducting nano-channels reveals the high spatial resolution of the technique.
The interface between LaAlO3 and SrTiO3 hosts a conducting two-dimensional electron system (2DES) characterized by several interesting properties. When the 2DES is confined in-plane to realize structures with a lateral size comparable to the characteristic length-scales of the system, mesoscopic effects emerge in electronic transport. Here, we present the properties of nanowires realized at the LaAlO3/SrTiO3 interface using the AFM-writing technique and hard masks of amorphous SrTiO3. We found that their magnetoconductance show signatures of coherent transport up to 1.5 K, and that nanochannels narrower than 100 nm undergo a metal-to-insulator transition at ~30 K. We attribute this behavior to the reduced system size using a model based on the saddle-point approximation of a quantum point contact.
We present novel quantum rings, which for example are fabricated from Rashba materials. These rings make use of the little explored interface between quantum mechanics and classical physics – their function is based on quantum collapses of electron wave packets combined with the coherent evolution of the quantum states. The devices feature fascinating properties such as unidirectional transport of matter waves and information. In particular, they reveal a fundamental inconsistency between quantum physics (including collapse processes) and the second law of thermodynamics.
The recent progress in the assembly of 2D van der Waals heterostructures has shown that it is possible to stack virtually every material out of this class enabling a truly unprecedented potential to discover new physical phenomena or to engineer novel electronic functionalities.Despite the vast scope of possibilities enabled by vdW interfaces, a systematic microscopic understanding allowing the interfacial electronic properties to be predicted in terms of those of the constituent monolayers is missing. Here, we develop a strategy based on band-alignment engineering which enables to build vdw interfaces which are either artificial semiconductors or artificial semi-metals.The results of optical and transport measurements demonstrate that the behavior of these interfaces is virtually indistinguishable from that of naturally existing 2D materials.
The anomalous Hall effect (AHE) can arise even in systems without a net magnetization provided that certain common symmetries are absent. Here, we present experiments on the layered antiferromagnet Co1/3NbS2, which exhibits AHE below the Néel temperature TN=29 K in the bulk. Our transport measurements on micro-fabricated devices reveal a pronounced anisotropy in the resistivity –indicative of the two dimensional (2D) character of the electronic properties– and show an extremely large AHE with an anomalous Hall conductance exceeding e2/h per layer at low temperature. This represents the first experimental observation of the AHE in the quantum limit in antiferromagnets, and –given the 2D nature of Co1/3NbS2– suggests the presence of topological bands originating from the magnetic superstructure.
Twisted graphene bilayers provide a versatile platform to engineer metamaterials with novel emergent properties by exploiting the resulting geometric moiré superlattice. We show that tuning the twist angle to $\alpha^*\approx 0.8^\circ$ generates flat bands with triangular superlattice periodicity. When doped with $\pm 6$ electrons per moiré cell, these bands are half-filled and electronic interactions produce a symmetry-broken ground state (Stoner instability) with spin-polarized regions that order ferromagnetically. Application of an interlayer electric field breaks inversion symmetry and introduces valley-dependent dispersion that quenches the magnetic order. With these results, we propose a solid-state platform that realizes electrically tunable strong correlations.
The Advanced Wakefield Experiment (AWAKE) recently demonstrated that a 400 GeV/c proton bunch can drive high amplitude plasma wakefields. To effectively excite wakefields, the drive bunch length should be on the order of the plasma electron wavelength (typically < 3mm). However, available proton bunches at CERN have an rms length of 6-12 cm. To be still able to excite high-amplitude wakefields, the experiment uses the plasma to modulate the bunch density, a process called the Seeded Self-Modulation. Transverse seed wakefields driven by the bunch in plasma act back on the bunch itself and periodically focus and defocus it, creating a microbunch train. This microbunch train can then resonantly excite a high amplitude plasma wakefield.
Using the two-screen diagnostic in AWAKE, we measured the transverse proton bunch distribution downstream the plasma exit and proved that: 1) a 400 GeV/c proton bunch self-modulates in plasma; 2) the driven wakefield amplitudes grows from their initial seed level along the bunch and along the plasma. In this contribution, we discuss the physics behind the seeded self-modulation process and show the experimental results.
The concept of lepton universality is a cornerstone prediction of the Standard Model (SM). In the last few years, hints of lepton universality violation have been observed in both tree-level $b \to c l \nu$ and rare $b\to sll$ beauty decays. These results, combined with the tensions observed in angular and branching fraction measurements of rare semileptonic decays, point to a coherent pattern of anomalies that could represent the first observation of Physics beyond the SM. This presentation will review these anomalies, will give an outlook for the near future and will discuss the way these measurements can be used to characterise possible New Physics scenarios.
Semi-leptonic b-baryon decays provide a unique means to investigate Lepton Flavour Universality (LFU) at the LHCb experiment. Sensitivity to New Physics (NP) contributions could show up in the angular observables of the decay products. In this work, the decay amplitude of the process $\Lambda_{b}\to\Lambda_{c}\,l\,\nu$ as a function of the squared di-lepton invariant mass and lepton helicity angle is studied. The angular analysis thus is performed to assess the feasibility of NP searches within this decay channel.
Using data from the LHCb experiment at CERN, a search for the lepton-flavour-violating decay $B^{+} \to K^{+} \tau^{\pm} \mu^{\mp}$ is being performed. This decay is forbidden in the standard model (SM) of particle physics because it violates the lepton-flavour conservation. However, it is known that the SM cannot account for dark matter, dark energy, the strong $CP$ problem, the neutrino masses, etc. In particular, this decay is interesting since there is emerging evidence for lepton-flavour non-universality, which can be linked to lepton-flavour violation via the introduction of leptoquarks.
In this talk, I will discuss selected aspects of an analysis designed to search for $B^{+} \to K^{+} \tau^{\pm} \mu^{\mp}$ decays using three-prong $\tau$ decays.
The family of decays mediated by $b \to s \ell^+ \ell^-$ transitions ($\ell = \mu, e$) provides a rich laboratory to search for effects of physics beyond the Standard Model. In recent years, LHCb has reported an anomalous behaviour in angular and branching fraction analyses of this decay, notably in one of the observables with reduced theoretical uncertainties, $P^{\prime}_{5}$. However, the vector-like nature of this pattern could be also explained by non-perturbative QCD contributions from charm loops, that are able to either mimic or camouflage NP effects. In this talk I will discuss the main features of this channel and present the latest results from LHCb.
Precision measurements of CP violating observables in beauty and charm hadron decays are powerful probes to search for physics effects beyond the Standard Model. The LHCb experiment is specifically designed to study these heavy hadron decays and is currently playing a major role in the field. One of its latest achievements is the first observation of CP violation in the charm sector. This talk will review the recent results from LHCb, including the mentioned discovery and several key measurements of CP violating observables in beauty meson decays, obtained exploiting the data collected during the Run 2 of the LHC.
A great step has been made recently in the field of CP violation in the charm sector, with the first observation of CP asymmetry by the LHCb collaboration (arXiv:1508.03054). A complementary approach to studying decay-rate asymmetries is investigating time-odd triple-product observables, which have the opposite dependence on the strong phase difference and thus complementary sensitivity to CP violation. We present an ongoing study using a novel triple-product asymmetry approach proposed by Durieux and Grossman (PRD92.076013) that uses angular-momentum dependent observables through natural spherical harmonics and angles between daughter particles. The study is performed on decays $D^0 \to K^+ K^- \pi^+ \pi^-$ and $D^0 \to \pi^+ \pi^- \pi^+ \pi^-$, with data collected by the LHCb experiment in Run2.
CP Violation (CPV) in the two-body decays of charm mesons was recently observed by the LHCb collaboration through the $\Delta A_{\mathrm{CP}}$ parameter. Current theoretical uncertainties cannot establish if this effect is due to physics beyond the Standard Model or not. Tests of CPV in the mixing or in the interference between mixing and decay might help clarify the picture. One way to probe these effects is to measure $y_{\mathrm{CP}}\equiv \hat{\Gamma}(D^0\rightarrow h^+h^-)/\hat{\Gamma}(D^0\rightarrow K^-\pi^+)$ where $h$ is a pion or a kaon. The main challenge is the determination of the detection efficiencies of the daughter particles to correct the reconstructed decay times of the $D^0$ mesons. This presentation will focus on an innovative data-driven approach to tackle this issue.
Superconducting circuits are a prime contender for realizing universal quantum computation in fault-tolerant processors and for solving noisy intermediate-scale quantum (NISQ) problems with non-error-corrected ones. Superconducting circuits also play an important role in state of the art quantum optics experiments and provide interfaces in hybrid systems when combined with semiconductor quantum dots, color centers or mechanical oscillators. In this talk, I will introduce the operation of superconducting circuits in the quantum regime and put quantum information processing with superconducting circuits into perspective with other solid state and atomic physics approaches. As one of two examples of our own research work in the area of fault tolerant quantum computing, which relies on the ability to detect and correct errors, I will present an experiment in which we stabilize the entanglement of a pair of superconducting qubits using parity detection and real-time feedback [1]. In quantum-error-correction codes, measuring multi-qubit parity operators projectively and subsequently conditioning operations on the observed error syndrome is quintessential. We perform experiments in a multiplexed device architecture [2], which enables fast, high-fidelity, single-shot qubit read-out [3], unconditional reset [4], and high fidelity single and two-qubit gates. As a second example, I will present the realization of a deterministic state transfer and entanglement generation protocol aimed at extending monolithic chip-based architectures for quantum information processing. Our all-microwave protocol exchanges time-symmetric itinerant single photons between individually packaged chips connected by transmission lines to achieve on demand state transfer and remote entanglement fidelities of about 80 % at rates of 50 kHz [5]. We believe that sharing information coherently between physically separated chips in a network of quantum computing modules is essential for realizing a viable extensible quantum information processing system.
[1] C. Kraglund Andersen et al., arXiv:1902.06946 (2019)
[2] T. Walter et al., Phys. Rev. Applied 7, 054020 (2017)
[3] P. Magnard et al., Phys. Rev. Lett. 121, 060502 (2018)
[4] J. Heinsoo et al., Phys. Rev. Applied 10, 034040 (2018)
[5] P. Kurpiers et al., Nature 558, 264-267 (2018)
In order to perform simulations of quantum systems on current quantum processors, quantum algorithms with short circuit depth have to be designed. Here, we experimentally demonstrate that exchange-type gates, tunable in amplitude and phase, are ideally suited for calculations in quantum chemistry [1]. We optimize and characterize these exchange-type gates, which yield an average gate fidelity of 95% obtained via randomized benchmarking. Finally, we determine the energy eigenstates of molecular hydrogen with an accuracy of 50 mHa using a variational quantum eigensolver algorithm based on exchange-type gates in combination with a method from computational chemistry to compute the excited states.
[1] M. Ganzhorn et al., Phys. Rev. Applied 11, 044092
Since the very first experiments, superconducting circuits are suffering from coupling to environmental noise, destroying quantum coherence and degrading performance. In state-of-the-art experiments, it is found that the relaxation time of superconducting qubits fluctuates as a function of time. We present measurements of such fluctuations in 2D and 3D-transmon circuits and develop a qualitative model based on interactions within a bath of background two-level systems (TLS) which emerge from defects in the device material. In our model, the time-dependent noise density acting on the qubit emerges from its near-resonant coupling to high-frequency TLS which experience energy fluctuations due to their interaction with thermally fluctuating TLS at low frequencies.
We will present recent experimental progress with micro-machined silicon nanomechanical systems. The interplay between parametric driving, interference and dissipation in a multi-mode cavity electro-optomechanical system can either be used to break time reversal symmetry and act as a compact on-chip microwave circulator [1], to realize bidirectional microwave to telecom conversion, or to deterministically entangle intinerant microwave modes [2]. Observation of such stationary entanglement not only reveals the quantum nature of the mechanical oscillator without measuring it directly, it also represents an important resource for quantum communication and quantum enhanced detection.
[1] Mechanical On-Chip Microwave Circulator. S. Barzanjeh, et al., Nature Commun. 9, 953 (2017)
[2] Stationary Entangled Radiation from Micromechanical Motion. S. Barzanjeh, et al. Nature, in print (2019)
Quantum illumination is a quantum sensing technique in which quantum correlation is used to improve the detection of a low-reflectivity object that is immersed in a bright thermal background. Here, using a superconducting circuit platform we experimentally implement quantum illumination at microwave frequencies. We use a Josephson parametric converter to generate stationary entanglement between microwave radiation and use the correlated photons to probe the region to detect the existence or absence of a target. We show that the signal-to-noise ratio of the microwave quantum-illumination system is superior to that of any classical microwave radar of equal transmitted energy.
Hole spins in Germanium offer the possibility for record manipulation times due to the strong spin-orbit coupling. In addition, they should be largely immune to hyperfine noise.
Here we present electrostatically defined quantum dots hosted in a two-dimensional Germanium hole gas. This approach provides excellent control over the measured system, which we can tune continuously from a single quantum dot to a double quantum dot. We demonstrate Pauli spin blockade and measure relevant material properties. From the large g-factor anisotropy we conclude that the confined states are mostly of heavy-hole type.
A resonant exchange qubit utilizes two orthogonal (S = 1/2, Sz = 1/2) states composed of three electron spins as the qubit states. We realize such a qubit in a GaAs triple quantum dot with each quantum dot hosting a single electron. We couple the electron spins strongly to individual GHz-photons in a strip-line resonator via a tunable electric dipole coupling. Under optimum conditions, the qubit is found to have a decoherence rate of less than 10 MHz at a qubit-resonator coupling strength of 23 MHz. In a further experiment, we use resonator photons to couple the resonant exchange qubit coherently to a superconducting transmon qubit.
Investigating charged molecules on insulating films is experimentally challenging. Atomic force microscopy, with single-electron sensitivity and capable of operating on insulating substrates, is a promising technique for such studies. Here we demonstrate multiple charge-state stabilization of molecules, induce intermolecular single-electron transfer and show that the charge state of a complex plays a role in its on-surface chemical reaction on multilayer insulating films. Moreover, we perform tunneling spectroscopy by using the atomic force microscope as a current meter, where we count single-electron tunneling events. This allows the quantification of the reorganization energy of a molecule on an insulating substrate.
Porphyrin-substrate hybrid systems are the building blocks in a series of materials, such as the organic light-emitting diodes, chemical sensors and dye-sensitized solar cells. Understanding and correctly describing the way molecules interact with the substrate upon adsorption hold the key to the prediction and improvement of the present-day devices.
Recently, distinct features were observed in the photoemission spectra of Co(II)-tetraphenylporphyrin on Mg(100) related to the molecular monolayer and film[1]. Here we investigate the structural and electronic changes the molecule undergoes upon deposition in the framework of hybrid density-functional theory and beyond it. Our simulations of adsorption at different surface sites give an insight into the underlying interaction as compared to the crystal.
[1] Franke et.al., Phys.Chem.Chem.Phys., 2017, 19, 11549-11553
Metal-organic interfaces are systems of great interest for both fundamental concepts in electronic structure theory and numerous promising technological applications. Recently, it was demonstrated that an insulating interlayer of MgO on an Ag(100) surface does not simply decouple the metal- and organic-layer but actively promotes charge transfer. While this has been shown for the case of pentacene on MgO/Ag(100)[1], it is interesting to further explore the conditions for charge transfer. Different molecular monolayers on the same surface are studied, aiming at revealing trends in terms of the molecule's electron affinity and size. Here, we present DFT calculations for monolayers of pentacene, PTCDA and H2TPP on MgO/Ag(100) and compare our results to experimental findings.
[1] M. Hollerer. ACS Nano 11, 6252-6260(2017)
Metal complexes containing gold in the formal oxidation state +I exhibit a very strong metallophilic interaction, which is often decisive for their arrangement in the solid state. To study this attractive interaction on surfaces, we investigated films with a thickness of just a few layers of 2-naphthyl-isonitrile-gold(I)-chloride on Au(111) and Au(110) surfaces. The physical vapor deposition was monitored by means of differential reflectance spectroscopy (DRS) and photoelectron emission microscopy (PEEM). After growth, the structures were characterized by means of scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). In fact, the Au(110)(1x2) reconstruction of the substrate surface is lifted upon adsorption of the molecules suggesting a sizable interaction between Au(I) complexes and the Au substrate.
On-surface synthesis allows to design carbon nanostructures such as graphene nanoribbons with atomic precision. However, the variety of conceivable structures critically depends on the number of available reaction concepts. Here, we present a new surface-assisted reaction allowing for the controlled fusion of two alkyl groups to form a phenyl ring. Scanning tunneling and non-contact atomic force microscopy images at different stages of the reaction along with DFT simulations allow to elucidate the reaction mechanism. Furthermore, we study the influence of surface templating by comparing the reaction on Au(111) and Au(110). The selective formation of phenyl rings by the fusion of alkyl groups on-surface is unprecedented, and introduces a powerful new motif in the design of novel nanomaterials.
Acenes are a class of polycyclic aromatic hydrocarbons that exhibit impressive semiconductor and open-shell properties. These unique properties can be tailored to potential applications by altering the conjugated π-system with chemical doping. The synthesis of large acenes via traditional solution-chemistry route is hindered by their poor solubility and high reactivity. In this work, we present the on-surface synthesis of undecacene doped with nitrogen atoms replacing the edge carbon atoms of the third outer benzenoid rings. The N-doped undecacene is characterized by scanning tunneling and non-contact atomic force microscopy on Au(111), supported by density functional theory and GW calculations. Furthermore, we use ab initio simulations to characterize the effects of the doping to the aromaticity and open-shell properties of the system.
Differential very low energy electron diffraction spectra have been measured on a Highly Oriented Pyrolitic Graphite (HOPG) surface in the range of landing energies from 0-1600eV. The reflectivity in the band gap, in between the interlayer resonances, differs from unity, implying that the vacuum wave function can penetrate the surface, but it is strongly damped via excitation of $\pi$- and $\pi +\sigma$-plasmon excitation. This is also true, albeit to a much lesser extent for wave functions for allowed states in the one electron band structure. Measurements of time correlated electron pairs (electron coincidence spectroscopy) show that Plasmon decay leads to emission of secondary electrons via the interlayer resonances. The results exemplify the momentum exciton picture of plasmon excitation and decay.
This study aims at direct imaging of contact resistance in MoS2-based thin film transistors (TFTs). Exfoliated single-crystal flakes of MoS2 have been used in a bottom-contact TFT configuration. Pyrimidine-containing self-assembled monolayers (SAMs) were employed to tune the work function of gold electrodes. Kelvin probe force microscopy measurements were carried out during operation of the devices in order to directly image potential drops across the channel and to study the influence of different SAM treatments on the contact resistance. By independently imaging potential drops at both carrier injection and extraction points, we demonstrate asymmetry of contact resistances in MoS2-based TFTs, as well as their non-linear and bias-dependent behavior.
InteractiveXRDFit is a Matlab program that calculates the X-ray diffracted intensity for heterostructures. The user can choose the substrate and the different materials composing an heterostructure among a long list of compounds, choose between (001) or (111) substrate orientation, and play with the different structural parameters (unit-cell size and number of layers). It is possible to build a superlattice composed of up to three different materials, and add a top and/or bottom layer. Each layer can have a different c-axis, either constant or varying as a function of depth within a layer. The simulation is quick and allows the user to compare it directly to the measurements, so as to rapidly determine the crystalline parameters of the sample.
The accumulation of amyloid fibrils is the hallmark of Parkinson’s and Alzheimer’s disease. We use atomistic and coarse-grain simulations to explore the intricate dynamics and aggregation of α-synuclein and amyloid-β(42), the proteins associated with these disorders.
We represent α-synuclein as a chain of deformable particles that can adapt their geometry, binding affinities and rearranges into disordered and ordered structures. Results offer valuable insight into the internal dynamics of α-synuclein and indicate that a protein attaching to a fibril gets trapped in sub-optimal configurations, explaining the experimentally observed stop-and-go-growth of an amyloid fibril.
We use atomistic simulations to explore the peptide dissociation from an amyloid-β(42) fibril. Simulations show structural stability of the fibrillar core and high flexibility registered at the tip.
Amyloid fibrils are the pathological hallmarks of many neurodegenerative diseases, including Alzheimer's and Parkinson's diseases, yet the mechanism of protein aggregation and fibrillization are not fully understood. Studying the protein aggregations in the microgravity/un-gravity condition can play a fundamental importance in discovering the aggregation mechanisms, and the influence of gravity on morphologies and configurations of aggregates as well as their aggregation behavior. In this research, we mainly focus on the low-gravity effect on alpha-synuclein aggregation in vitro, and combined various techniques, including atomic force microscope (AFM), Thioflavin T (ThT) and circular dichroism (CD), to measure the morphological transformation, aggregation kinetics, secondary structural transition during aggregation, and reasonable achievements have been achieved.
A transient state of the excess electron in liquid water preceding the development of the solvation shell, the so-called wet electron, has been invoked to explain spectroscopic observations, but its properties have remained elusive. Here, we carry out hybrid functional molecular dynamics to unveil the ultrafast mechanism leading to the hydrated electron. In the pre-hydrated regime, the electron is found to repeatedly switch between a quasi-free electron state and a localized state with a binding energy of 0.26 eV, which we assign to the wet electron. This state self-traps in a region of the liquid which extends up to 4.5 Å and involves a severe disruption of the hydrogen-bond network. Our picture provides an unprecedented view on the wet electron.
The method of infrared nanospectroscopy and high spatial resolution imaging by photothermal induced resonance (PTIR) proved its viability and utility for many studies. We discuss our results on development of the method in visible spectral range. Its performance was enhanced by both factors: the coincidence of the resonant frequency of an AFM tip dithering with the laser pulse repetition range, and plasmon gap resonance. In the visible, the latter is very sensitive to the properties, first of all thickness, of the sample studied, and this dependence may create a contrast mechanism for the imaging even in the case of inefficient light absorption. We present a few nm resolution images of chlorophyll a monolayers and amyloid fibrils.
Exploiting the benefits of the two types of forces from optical and acoustic trapping schemes in a single setup allows us to manipulate biological samples in a contact-free and non-invasive way. With our system we levitate sub-millimeter sized samples in solution on a microfluidic chip compatible with various optical imaging techniques. We have developed a 3D ultrasonic resonator with custom made transducers to optimize the acoustic power transfer and controllability. The combination with optical tweezers allows for force estimations, increased precision in patterning, manipulation and induced rotation of the sample for optical tomography. Long-term monitoring of samples without mechanical confinement would potentially be a valuable tool for studying embryos, cell clusters and organoids for development- and drug-screening purposes.
Crystallization is often suppressed by point defects due to larger impurity particles. Surprisingly, microgels can overcome this limitation: Large microgels can spontaneously deswell to fit into the crystal lattice of smaller but otherwise identical microgels. We find this unique reduction of polydispersity and particle deswelling to be triggered by a difference in osmotic pressure between the inside and the outside of the microgel particles that is set by counterions. We find the freezing point of polydisperse and bidisperse pNIPAM suspensions to be linked to particle deswelling. In comparison to hard, incompressible colloidal particles, this particle deswelling mechanism fundamentally changes the role of polydispersity in microgel suspensions.
Here, we have studied the magnetically ordered phase of Ca2RuO4 at T = 16 K, using O-K edge Resonant Inelastic X-ray Scattering technique. Four
excitations have been identifed- 2 low energy exci-
tations at 80 meV and 400 meV respectively and two high energy excitations at energies 1.3 eV and 2.2 eV . The low energy peaks are interpreted
to be arising from composite spin- orbital excitations
due to spin orbit coupling and the high energy ex-
citations arise from singlet-triplet
excitations at the Ruthenium site set by
Hund's coupling. With the light polarisation analysis of the x-ray
absorption and the RIXS spectra, we were able to
characterise the mott active Ruthenium orbitals in-
volved in the absorption processes.
Whether the magnetic excitations in doped cuprates are described by paramagnons or the continuum of charge and spin excitations of correlated electrons is still controversial. Recent RIXS studies with azimuthal-dependent measurements for polarization analysis demonstrated how charge and spin nature of the low-energy excitations can be resolved, providing thereby a way to study their properties separately. Here we studied the evolution of the charge and spin components of the excitations by azimuthal-dependent RIXS in the phase diagram of Bi2Sr2CaCu2O8+x. Possible renormalizations by superconductivity of both kinds of excitations are explored by comparing their changes above and below Tc. Our results help to elucidate the nature of the magnetic excitations in cuprates and their possible correlations to superconductivity.
We investigate the internal structure of the domain walls (DWs) in Tm3Fe5O12 (TmIG) and TmIG/Pt bilayers and demonstrate their efficient manipulation by spin-orbit torques with velocities of up to 400 m/s and current threshold for DW flow of 5x10^6 A/cm^2. Pt current lines patterned on extended TmIG films allow controlling DW propagation and magnetization switching in selected regions. Scanning nitrogen-vacancy magnetometry reveals that the DWs of thin TmIG films are Néel walls with left-handed chirality, with the DW magnetization rotating towards an intermediate Néel-Bloch configuration upon deposition of Pt. These results indicate the presence of a sizable interfacial Dzyaloshinskii–Moriya interaction in TmIG, which leads to novel possibilities to control the formation of chiral spin textures in centrosymmetric magnetic insulators.
Co$_x$Zn$_{1-x}$O – Permalloy (Py) heterostructures were investigated with frequency-dependent ferromagnetic resonance (FMR), x-ray magnetic circular dichroism (XMCD) and SQUID magnetometry. At low temperatures Co$_x$Zn$_{1-x}$O is an uncompensated antiferromagnet showing a narrowly opened hysteresis and a vertical exchange-bias effect [1,2]. By means of SQUID a static interaction is evidenced by increased coercive fields for Py at low temperature in the Co$_x$Zn$_{1-x}$O – Py system. The dynamic interaction is measured by using FMR from 3-12GHz. We find an increasing frequency dependence of the homogeneous broadening of the FMR linewidth with increasing Co concentration evidencing spin pumping from Py into Co$_x$Zn$_{1-x}$O.
[1] V. Ney et al., Phys. Rev. B 94, 224405 (2016).
[2] M. Buchner et al., Phys. Rev. B 99, 064409 (2019)
La$_2$NiMnO$_6$ (LNMO) is an insulating double perovskite oxide with ferromagnetic Curie temperature around 280K driven by the oxygen-mediated super exchange interaction between long-range ordered Ni$^{2+}$ and Mn$^{4+}$ ions. An insulating ferromagnet would be ideal for novel spintronic devices but only a few attempts of growing ultrathin films have been reported.
Here we show that the epitaxial growth of LNMO ultrathin films can be accomplished with off-axis RF magnetron sputtering. Structural characterization illustrates the preparation of films with high crystalline quality and minimal degree of antisite disorder. SQUID magnetometry and synchrotron XMCD indicate that the ferromagnetic character of the film is retained at least down to 2nm. This is one important step towards the implementation of LNMO films in multilayer geometries.
Since many years, rare earth nickelates attract the researchers interest due to their huge variety of fascinating physical properties which are tunable by the interplay of electron correlations and crystal structure. Further, these systems show dimensionality-driven transitions (e.g. LaNiO3 (LNO) thin films), and strain-induced transitions (e.g. NdNiO3 heterostructures).
We investigate the evolution of the electronic structure of LNO thin films in proximity to doped L1-xSxMnO3 (LSMO) grown on STO and NGO substrates by pulsed laser deposition (PLD). The combined study of angle resolved photoemission spectroscopy (ARPES) and transport measurements demonstrates that the electronic properties of LNO thin films can be tuned via the LSMO buffer layer. The results will be explained in terms of charge transfer mechanism and electron-phonon coupling.
Many perovskite transition metal oxides (TMOs) exhibit metal-insulator transitions whose complex physics is not fully understood. We use soft-X-ray ARPES to visualize how the electrons delocalize and couple to bosonic lattice excitations in CaMnO3 upon its doping with Ce. We show the progressive development of a complex Fermi surface where mobile electrons weakly coupled to lattice coexist with much heavier charge carriers formed by strongly coupled polarons. The latter originate from a boost of electron-phonon interaction (EPI) when the populated bandwidth becomes of the order of phonon energy, breaking down the Migdal theorem and invoking high-order terms of EPI. Our results shed light on the complex transport response of Ce-doped CaMnO3 and suggest strategies to engineer TMO-based quantum matter.
SrMnO3 can be strain-engineered to be multiferroic, with coexisting and tuneable magnetic and ferroelectric (FE) order. We recently showed, using first principles calculations, that the ferroic strain-temperature phase diagram of SrMnO3 accommodates a tetracritical point (TCP) with coinciding magnetic and FE ordering temperatures.
Here, we construct a Landau theory with parameters determined from first principles DFT and effective Hamiltonian calculations, and demonstrate large magnetoelectric coupling, several orders of magnitude larger than in conventional magnetoelectrics, occurring near the TCP. We study a giant magnetic cross-caloric effect, increasing the electrocaloric effect by 60%, providing an example of a large, useful magnetoelectric coupling effect in an antiferromagnetic multiferroic. This opens new possibilities for promising research directions among caloric effects for solid state cooling.
We explore the interplay of electron-electron correlations and spin-orbit coupling in the model Fermi liquid Sr2RuO4 using laser-based angle-resolved photoemission spectroscopy. Our precise measurement of the Fermi surface confirms the importance of spin-orbit coupling and reveals that its effective value is enhanced by a factor of about two, due to electronic correlations. The self-energies for the β and γ sheets are found to display significant angular dependence, which arises from a substantial orbital mixing induced by spin-orbit coupling and does not imply momentum dependent many-body interactions. A comparison to single-site dynamical mean-field theory further supports the notion of dominantly local orbital self-energies, and provides strong evidence for an electronic origin of ‘kinks’ in the quasiparticle dispersion of Sr2RuO4.
We have performed soft x-ray angle-resolved photoemission spectroscopy (ARPES) measurements on overdoped La-based cuprates La$_{2-x}$Sr$_x$CuO$_4$ and Eu$_{0.2}$La$_{1.8-x}$Sr$_x$CuO$_4$, and investigated the band structure in three-dimensional momentum space. While nodal part of the Fermi surface was $k_z$ independent, significant $k_z$-dispersion was unveiled in the antinodal portion. From the band structure fitted to the tight-binding model, we have demonstrated that the significant $k_z$ dispersion suppresses the enhancement of the density of states (DOS) by van-Hove singularity (VHS). Our results suggest that the enhancement of electronic specific heat observed in La-based cuprates is caused by quantum criticality rather than by simple DOS divergence at VHS.
Charge order (CO) and the connection to electron-phonon coupling (EPC) play crucial role in the low-energy regime of quasi-one-dimensional ladder materials. Characterizing the relevant excitations provides a direct tool to assess the underlying complex interactions. Resonant inelastic X-ray scattering (RIXS) is a powerful technique for probing phonons and its interplay with CO. We investigated the CO and optical phonon excitations in the two-leg ladder subsystem of Sr14(Cu,Co)24O41 using O K-edge RIXS and X-ray absorption spectroscopy (XAS). We infer a continuous shift of the CDW ordering towards Γ-point with Co doping, with a 5-10 meV softening of the bond-stretching phonon mode (~65 meV) at the ordering vector. This is accompanied by a reduction in the ladder hole density determined from XAS.
Studying the prototypical ferromagnetic superconductor UGe$_2$ we demonstrate the potential of the Modulated IntEnsity by Zero Effort (MIEZE) technique—a novel neutron spectroscopy method with ultra-high energy resolution of at least 1 $\mu$eV—for the study of quantum matter. We reveal purely longitudinal spin fluctuations in UGe$_2$ with a dual nature arising from $5f$ electrons that are hybridized with the conduction electrons. Local spin fluctuations are perfectly described by the Ising universality class in three dimensions, whereas itinerant spin fluctuations occur over length scales comparable to the superconducting coherence length, showing that MIEZE is able to spectroscopically disentangle the complex low-energy behavior characteristic of quantum materials.
In 3D, only time-reversal ($\mathcal{T}$) and inversion ($\mathcal{I}$) symmetries are essential for superconductivity. We examine the 2D case and find that $\mathcal{T}$ and $\mathcal{I}$ are not required, and having a combination of either symmetry with a mirror operation ($M_z$) on the basal plane suffices. Combining energetic and topological arguments, we classify superconducting states without $\mathcal{T}$ and $\mathcal{I}$ present, a situation encountered in several experimentally relevant systems. With only $\mathcal{I}$ combined with $M_z$, the system is generically fully gapped, potentially with topologically-protected chiral edge modes. All other cases do not support chiral Majorana edge states, but the superconductor can have point nodes with associated topologically-protected flat-band edge modes. Our analysis provides guidance on the design and search for novel 2D superconductors.
HEAs are a new class of materials that consist of several principal elements arranged on simple lattices, stabilized by the high-configurational-entropy of the random mixing of the elements. In this presentation, we will show that the properties of this superconducting high-entropy alloy are strongly related to the valence electron count and that the superconducting transition temperatures $T_c$ of these alloys fall between those of analogous crystalline and amorphous materials. We find that despite the large degree of randomness and disorder in these alloys, the superconducting properties are nevertheless strongly dependent on the chemical composition and complexity. We argue that high-entropy alloys are excellent model systems for understanding how superconductivity and other collective quantum states evolve from crystals to amorphous solids.
The actinide superconductor ThFeAsN exhibits a $T_c$ of 30 K without doping or external pressure. Formally similar to LaFeAsO and predicted to be an antiferromagnet, surprisingly, the new material does not show any magnetic order.
Based on results of a series of ambient- and high-pressure experiments and DFT calculations [1,2], we show how ThFeAsN combines the peculiarities of unconventional superconductivity with those of correlated electron systems. We further compare the role of charge doping vs. structural distortions and argue why the “structural route” to superconductivity is so unusual in iron-based compounds.
We present a measurement of charm-mixing parameters in $D^0 \rightarrow K^0_S \pi^+ \pi^-$ decays with a model-independent method on data collected by the LHCb collaboration in 2011-2012 [arXiv:1903.03074], and the prospects for an improved analysis using the 2016-2018 data. The analysis measures the dimensionless parameter $x$ related to the mass difference between the mass eigenstates of the $D^0$ meson, whose current world-average value is still zero within uncertainty. $D^0$ candidates are reconstructed from $D^{*-} \rightarrow D^0 \pi^-$ and $B^- \rightarrow D^{0}\mu^{-}X$ decays. The statistical uncertainty on $x$ in the new analysis is expected to reach $\mathcal{O}(10^{-4})$ when combining both samples. We present sensitivity studies using the 2016-2018 data and discuss approaches to improve the precision beyond the increased statistics.
Direct and indirect CP violation is observed in particle decays. The latter usually includes oscillations between a neutral meson and its antiparticle. ATLAS measures this type of CP violation in the decay Bs -> J/psi + phi, with J/psi -> µ+µ- and phi -> K+K-, mainly because it is sensitive to higher order effects and therefore to deviations from known physics. Here the quantity of interest is the so-called weak mixing phase phi_s. Latest results will be presented and compared to similar analyses from other LHC experiments as well as with the expectation from the Standard Model.
The amplitudes describing the decays of neutral b-hadrons to charmless (quasi)-two-body final states receive contributions from b→u tree and b→d,s penguin topologies. This rich landscape of interfering amplitudes allows interesting CP-violation measurements to be performed. In the case of B decays to two vector particles, a full amplitude analysis also provides insight in the so-called polarisation puzzle. In this work, a set of CP-violating observables is measured using $B^0$ meson decays reconstructed from the ($π^+π^−$)($K^+π^−$) quasi-two-body final state. The CP-averaged polarisation fractions and phase differences among the contributing amplitudes are also reported. The analysis uses 3fb$^{−1}$ of data collected during LHCb Run I and consists of the first full amplitude study of this decay mode.
A long standing tension between measurements of the CKM matrix element $V_{\rm ub}$ in inclusive and exclusive decays can be eased by introducing a small right-handed weak current.
By measuring the differential decay rate of the semileptonic decay $B^{+}\rightarrow\rho^{0} \mu^{+} \nu_{\mu}$, using data from the LHCb experiment, a bound on a possible right-handed weak current can be set. This talk will focus on the first steps of the analysis where a new signal-reconstruction approach has been studied. The development and performance of a multivariate algorithm used to separate signal and background will also be presented, and finally, the status and future steps of the analysis will be discussed.
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.
A measurement of the Higgs-beauty quark coupling through the Higgs boson production associated with a Z or W boson in the lepton + beauty final state is presented. The analysis is based on 41.3/fb data from p-p collisions at 13 TeV collected by CMS in 2017. When combining with the analyses on the 7, 8 and 13 TeV energies, a 125.09 GeV Higgs boson is measured (4.8 sigma significance).
The combination of this measurement with other CMS analyses of a Higgs boson decaying to beauty quarks observed a significance of 5.6 sigma.
Measuring the top quark Yukawa coupling is an important test of the standard model (SM) of particle physics and the production of a Higgs boson in association with top quarks (ttH) is the only channel that allows a direct measurement of this SM parameter. This talk will focus on the measurement of ttH where the Higgs boson decays to bottom quarks. The data were collected by the CMS experiment in 2017 at a center-of-mass energy of 13 TeV at the LHC. Because of the small cross section and challenging final state, sophisticated methods for signal/background rejection as well as signal extraction are required.
A search for direct top squark pair production is presented using Run 2 ATLAS data in final states containing at least three leptons and missing transverse momentum. Naturalness considerations suggest the third generation squark masses should be around the TeV scale and hence could be produced at LHC.
Models are considered where a pair of the heavier top squark mass eigenstates is produced, which decay into the lighter top squark and a Z boson. The light top squark subsequently decays into a top quark and the lightest neutralino. The leptonic decay of the Z bosons is exploited in addition to the missing transverse momentum from the neutralinos in order to discriminate against background Standard Model events.
The measurement of low-mass $\rm e^+e^-$ pairs is a powerful tool to study the properties of the Quark-Gluon Plasma (QGP) created in ultra-relativistic heavy-ion collisions. Since such pairs do not interact strongly and are emitted during all stages of the collisions, they allow us to investigate the full time evolution and dynamics of the medium created.
Measurements in pp and p-Pb collisions are the necessary reference for heavy-ion studies.
In this contribution, I will present low-mass dielectron measurements with the ALICE detector at LHC, in pp, p-Pb and Pb-Pb collisions at different energies. The results will be compared with the expected dielectron yields from known hadronic sources and with theoretical predictions.
High-impedance devices, such as quantum devices, are difficult to measure fast, due to the large impedance mismatch between the quantum device and 50 Ohm wave impedance of RF circuits. Fast and reliable read-out requires impedance matching, which is achieved through a resonant circuit. We compare two approaches, a) a lumped LC- and b) transmission line resonator on a quantum dot (QD) of which we measure its shot noise. We have tested the two approaches on QDs defined in a single carbon nanotube. We typically find suppressed shot-noise as expected for and in agreement with sequential tunneling through a QD. However, we also find regions of enhanced shot noise within and outside of Coulomb-blockade (CB). We explain this by blocking states.
We investigate a two-dimensional electron system (2DES) embedded in an optical cavity. Cavity photons are strongly coupled to Fermi polarons, which leads to the formation of polaron-polaritons [1, 2, 3]. The light-matter coupling strength is sensitive to the electronic ground state. As the magnetic field is varied, we find that not only the energy of the polariton but also their scattering amplitude is changed.
We observe nonlinear energy shifts in the lower and upper polariton lines at certain 2DES filling factors and concomitant enhancements in the electron-polariton scattering amplitude.
References
[1] S. Ravets, et al., Phys. Rev. Lett. 120, 057401 (2018).
[2] M. Sidler, et al., Nature Phys. 13, 255 (2017).
[3] S. Smolka, et al., Science 346, 332 (2014).
Magic states were introduced in the context of Clifford circuits as a resource that elevates classically simulatable computations to quantum universal capability, while maintaining the same gate set. Here we study magic states in the context of matchgate (MG) circuits, where the notion becomes more subtle, as MGs are subject to locality constraints and also the SWAP gate is not available. Nevertheless a similar picture of gate-gadget constructions applies, and we show that every pure fermionic state which is non-Gaussian, i.e. which cannot be generated by MGs from a computational basis state, is a magic state for MG computations. This result has significance for prospective quantum computing implementation in view of the fact that MG circuit evolutions coincide with the quantum physical evolution of non-interacting fermions.
In this work we relate the physics of time to information theory via a simple question: how many bits of information do we gain when we read off the value of a clock?
Our motivation is to understand from an operational point of view how much information clocks provide about time. Doing so would allow us to connect the performance of clocks with basic quantities in physics, such as size, energy and thermodynamic resources. Furthermore, this will be beneficial in establishing general results characterizing the cost of communication of time-information in clock networks.
We present a measure of information based on a relative entropy between real clocks and "zero-information" clocks, and demonstrate that it unifies existing quantifiers of accuracy.
Topological insulators are materials that have a gapped bulk energy spectrum but contain protected in-gap states appearing at their surface. These states exhibit remarkable properties such as unidirectional propagation and robustness to noise that offer an opportunity to improve the performance and scalability of quantum technologies. For quantum applications, it is essential that the topological states are indistinguishable. We report high-visibility quantum interference of single-photon topological states in an integrated photonic circuit. Two topological boundary states, initially at opposite edges of a coupled waveguide array, are brought into proximity, where they interfere and undergo a beamsplitter operation. We observe Hong-Ou-Mandel interference with 93.1 ± 2.8% visibility, a hallmark nonclassical effect that is at the heart of linear optics–based quantum computation.
New cutting edge technology developed in Poland allows obtaining the complete information from high energetic photons undergoing Compton scatterings. This in turn enables for the first time to read out the quantum information from the molecular environment, i.e. to study the quantum computing in metabolic processes in human beings. This new information may be related e.g. to cancer in humans as our pilot studies suggest.
The Poster Session is held on Wed 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 Wed.
The sensitivity of 3D magnetohydrodynamical equilibria to the toroidal current profile is of paramount importance for stellarator optimization and operation. In fact, magnetic field-line chaos can emerge depending on the plasma pressure and currents, thereby strongly affecting particle confinement. The Stepped-Pressure Equilibrium Code (Hudson et al., Phys. Plasmas, vol 19 (11), 2012) can be used to compute partially reconnected equilibria with coexisting magnetic surfaces, magnetic islands and chaos. The code has been recently extended to allow toroidal current prescription. A study of the toroidal current effect on magnetic topology is presented in a simplified stellarator configuration.
Electron-Cyclotron waves are an important tool in tokamak devices for core heating, current drive and MHD mode stabilization. Density fluctuations at the edge can cause a broadening of the EC beam before absorption, potentially leading to inaccurate or less efficient power deposition, especially in large tokamak devices. This can be modeled with the quasilinear Fokker-Planck code LUKE, using a dedicated fluctuation module. Experimental constraints are added to the model by measuring Hard X-Ray Bremsstrahlung emission from the plasma using a spectroscopic 4-camera HXR system. Modeling can be augmented using a COMSOL RF solver, coupled with the Global Braginskii Solver that estimates density fluctuations in the Scrape-Off Layer.
The Poster Session is held on Wed 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 Wed.
With the misuse of antibiotics, antimicrobial resistance becomes a very serious public health issue. Proposed technique of antibiotic sensitivity characterization is based on the bacterial nanomotion. The organism of interest is attached onto a cantilever and nanoscale movements induce cantilever oscillations. If the organism is exposed to an antibiotic to which it is sensitive, the oscillations stop.
Alternative approach to conventional AFM, based on the use of light-transmitting polymer as a waveguide and cantilever at the same time, allows to have simple parallel optical readout. Light can be coupled into several waveguides simultaneously, to collect signal from several output lightspots with a CCD camera. Custom design of the cantilevers also gives possibility of micropatterning of cantilever surface with microorganisms.
We simulate how droplets released from a linear droplet generator arrange themselves in a three-dimensional way within a surrounding hull. During this arrangement process, droplets touching each other can form bilayers, which then can be broken up and reformed again. For studying this process, we perform macroscale Monte Carlo movement simulations with a simplified rule set for the slowing down and acceleration of droplets, embedding some extent of randomness in the change of movement and in the probabilities for bilayer formation and destruction. We aim at qualitatively reproducing the three-dimensional structures achieved in experiments performed by our EU project partners in Cardiff. As a next step, we aim at predicting the experimental outcome.
The Poster Session is held on Wed 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 Wed.
We study the electronic transport properties of weakly coupled 1µm-large quantum dots (QDs) defined in GaAs/AlGaAs-heterostructures in the integer and fractional quantum Hall regime. Between filling factor 2 > ν > 1, the Coulomb resonances observed in the current through the QD are modified whenever an electron tunnels between the two Landau levels. Additionally, we employ charge detection and real-time counting techniques to measure tunneling between the Landau levels time-resolvedly. We observe similar behaviour for the first time in the fractional QH regime ν < 1. The presented investigations pave the way for time-resolved measurements of quasiparticle tunneling between fractional QH states predicted to exhibit anyonic statistics.
Rigid tannin-furanic foams are porous materials synthetized from wood industry products, and have potential applications as new materials for green-building technology, and possibly also for waste water purification. Within the Interreg Italy-Austria ITAT1023 InCIMa project (2017-2019), foam samples synthetized under varying chemical conditions at the Salzburg University of Applied Sciences have been characterized by Raman spectroscopy at the University of Salzburg and at the IUVS beamline of the Elettra synchrotron in Trieste. The additional synergistic complementation with several analytic techniques available at the Elettra synchrotron through the beamlines SISSI (Infrared), SYRMEP (microtomography), and SAXS (small angle X-ray scattering), performed within several CERIC proposals, enables us to more deeply characterize, and in future subsequent steps optimize, these materials.
A detailed characterization of the mechanical performance, such as tensile strength, heat deflection temperature, compressive strength as well as impact strength, of 3D-printed wood-fiber-reinforced biocomposites was carried out as a function of various infill pattern orientations. Two wood filaments differing in terms of wood fiber content were utilized for specimen production, using a commercially available FDM 3D printer. All FDM 3D printed samples were evaluated depending on the infill orientation and on the wood fiber content. It could be proven that all investigated mechanical characteristics of the FDM 3D-printed wood-fiber-reinforced biocomposites are heavily dependent on the wood fiber content and on the infill pattern orientation. This study has been conducted within the international project Interreg Austria-Bavaria AB97 TFP-HyMat.
Magnetic three-dimensional structures on the nanoscale possess static and dynamic properties not found in their ‘flat’ counterparts. The recent development of three-dimensional lithography and probing techniques (such as X-ray tomography) has enabled the experimental investigation of such structures. Concurrently, simulations need to be developed to gain detailed understanding of the magnetization dynamics. We have developed a finite-element meshing technique involving Eikonal equations, which has allowed us to produce high-quality efficient meshes for to describe a mesoscopic ‘Buckyball’ made of hollow beams, exemplifying a complex network with tree-fold junctions. Our micromagnetic simulations based on tetrahedral meshes reveal reversal avalanches mediated by the nucleation and propagation of domain walls during the field-driven magnetization reversal in the cylindrical tubes making up the Buckyball.
The investigation of quantum phenomena in solid state systems requires the ability to cool down macroscopic samples to low temperature. Lowering the temperature allows said quantum phenomena to develop and emerge in experiments. In semiconducting devices and at millikelvin temperatures, the cool down of an electron gas is increasingly challenging due to vanishing thermal conductivities and the freezing-out of phonons.
We measured ultra-low electronic temperatures in a cryogen-free dilution refrigerator with a base temperature below 4 mK, achieved by using low-noise read-out and an innovative He4 immersion cell for improved thermalization of the sample. With this setup we can perform experiments at extremely low electronic temperatures and in high magnetic field on gate-controllable nanostructures.
We show that non-local orbits can arise in the presence of time-reversal symmetry (TRS), via full-lattice simulations of a system with four Weyl points subjected to an axial field [1,2]. Magnetic field, applied to a system with Weyl points, results in pseudo-Landau levels that disperse only along the field direction [3]. An appealing idea is to avoid breaking TRS, and rely on an axial field. We elucidate the interpretation of the orbit surface motion in the absence of an external magnetic field, and verify the semiclassical energy quantization by an effective surface theory approach.
[1] Grushin et al., PRX 6, 1 (2016).
[2] Peri et al., Nat. Phys. 15, 357 (2019).
[3] Potter et al., Nat. Commun. 5, 5161 (2014).
We present measurements of quantized conductance in a quantum point contact (QPC) defined entirely by electrostatic gating of a high-mobility InAs quantum well. Spin splitting is observed separately when applying a magnetic field in either parallel or perpendicular direction and in the latter case it is superimposed by magnetic depopulation. We resolve the energy levels of the QPC by finite bias spectroscopy and determine the g-factor for both magnetic field directions.
Minute control over nanostructures of InAs is an important step towards potential applications such as topological quantum computing for which it is a prime candidate due to its high spin-orbit interaction and a low effective mass.
We propose an exact construction for atypical excited states of a class of non-integrable quantum many-body Hamiltonians in one dimension (1D), two dimensions (2D), and three dimensions (3D) that display area law entanglement entropy. These examples of many-body “scar” states have, by design, other properties, such as
topological degeneracies, usually associated with the gapped ground states of symmetry protected topological phases or topologically ordered phases of matter.
The orthorhombic (Pbnm) HoMnO3 is of particular interest due to its high magnetically-induced polarization values and magnetoelectric coupling strength. The high magnetic frustration results in a magnetic order that creates a distortion in the crystal lattice. This distortion breaks inversion symmetry and creates a macroscopic electric polarization P along the a-axis.
We investigated the broken symmetry of Pbnm in thin films of HoMnO3 at low temperature and the relation between the magnetic order and the structural distortion. Forbidden reflections for Pbnm show that the distortion does not exclusively affect to the atomic position along the polar axis. Moreover, studying reflections with component along the polar axis reveals the polar distortion directly, visualized by the difference diffraction intensity from opposite domains.
Here, we present results of ultrasound investigations of the frustrated Tb$_2$Ti$_2$O$_7$. This cubic material features a Curie-Weiss temperature of $\theta_{\text{CW}} = - 19$ K, but no magnetic ordering has been detected down to 50 mK, indicating a large frustration factor.
Our ultrasound results evidence a strong spin-lattice coupling in Tb$_2$Ti$_2$O$_7$. We observed pronounced minima in the sound velocity of different acoustic modes at 0.5 K and an additional anomaly at approximately 0.15 K. Below 0.5 K, the acoustic properties show a pronounced thermal hysteresis. Moreover, some anomalies have been detected in magnetic fields applied along the [110] direction.
Possible quadrupolar ordering and a spin-liquid state are discussed for Tb$_2$Ti$_2$O$_7$ in relation to our experimental observations.
We present a method on how to calculate analitically the energy splitting between the two lowest levels of spin models on non-frustrated clusters in lowest-order degenerate perturbation theory. We apply it to arbitrary size 1D chains and small 2D and 3D clusters and find that by tunning an external magnetic field, the ground can be made degenerate on N different fields, where N is the number of spins. We argue that this phenomena is independent of the geometry, requiring only competing terms in the model. We study the effect of disorder on the position of the crossings and on the tunneling rate to further show the robustness of the zeros.
Layered transition metal dichalcogenides are intensively investigated due to their rich optoelectronic, superconducting and topological properties and their potential usage as mono-layer building blocks. Surprisingly, in semiconducting 2H-MoTe$_2$ long-range magnetic order of unknown origin has recently been observed [1]. Here we present the full 3D band structure of 2H-MoTe$_2$, determined with soft X-ray ARPES. We find a pronounced k$_z$ dispersion in most bands, consistent with ab-inito calculations. Furthermore, we present results of beta detected $^8$Li NMR measurements and show that the spin-lattice relaxation of the implanted Li ions is inconsistent with ferromagnetic order. Instead, our results suggest a magnetic structure that is coupled antiferromagnetic across the van der Waals gap.
[1] Z. Guguchia, et. al., Sci. Adv. 4, eaat3672 (2018)
We report the discovery of magnetic order in bulk semiconducting transition metal dichalcogenides (TMDs) 2H-MoTe2 and 2H-MoSe2 [1]. The muon spin rotation (muSR) measurements show the presence of long-range magnetic order in both compounds. DFT calculations show that this magnetism is promoted by the presence of defects in the crystal. The STM measurements show that the vast majority of defects in these materials are metal vacancies and chalcogen-metal antisites. DFT indicates that the antisite defects are magnetic with a magnetic moment in the range of 0.9 to 2.8 muB. These observations establish 2H-MoTe2 and 2H-MoSe2 as a new class of magnetic semiconductors.
[1] Z. Guguchia et. al., Science Advances 4, eaat3672 (2018).
Zinc oxide is a rather new material for optoelectronic applications. Due to its high LO phonon energy (ELO~72 meV), it is suitable for THz-devices like quantum cascade lasers (QCLs), which are currently limited to operation temperatures around ~200 K for typical GaAs material systems.
In this work, we show the development of a full fabrication process for double metal waveguides, processed into ZnO/ZnMgO QCL structures. This includes the development of a CH4-based RIE dry etching process with additional passivation for preventing surface leakage, a thermo-compression bonding (wafer bonding) with a substrate removal procedure and the fabrication of low-resistance ohmic contacts. In addition, we will present first photoluminescence measurements from such ZnO-based QC structure at liquid nitrogen temperatures and above.
We report magnetic investigations of a novel Kagome-related compound. Single crystals of the compound Cu2OSO4 have been studied by neutron scattering, magnetization and susceptibility. We find that instead of the spin-liquid ground state expected for a kagome compound, Cu2OSO4 orders in a canted anti-ferromagnetic structure. The magnetic structure is solved through neutron diffraction. The phase diagram established through susceptibility and specific heat measurements. Inelastic neutron spectra are being analyzed to determine the magnetic exchange pathways, and eventually explain the observed behavior.
RNiO3 (R = trivalent rare earth ions) perovskites are a unique class of materials, where structural, electric and magnetic transitions are directly linked to the size of the incorporated rare earth ion. The transitions are temperature dependent, which allows a systematic study. Of special interest in this series is where the transition point reaches 0K, which creates a frustrated system with several coexisting properties. With the unique equipment at PSI in Villigen we are able to synthesize RNiO3 at high temperatures (up to 1200 °C) and high O2 pressures (up to 2 kbar) in a scale of 5-10 g, suitable for neutron experiments. La/Pr perovskites of the type RNiO3 (R = LaxPr1-x ; x = 0.1 to 1.0) are presented.
We present an infrared spectroscopy study of ZrTe$_5$, which realizes a recent theoretical proposal that this material exhibits a temperature-driven topological quantum phase transition from a weak to a strong topological insulating state through an intermediate Dirac semimetal state around $T_p \simeq$ 138K. Our study details the temperature evolution of the energy gap in the bulk electronic structure. We found that the energy gap closes around $T_p$ where the optical response exhibits characteristic signature of a Dirac semimetal state. A comparison with previous studies suggests that the divergent results and conclusions about the topological nature of ZrTe$_5$ can be reconciled by a variation of $T_p$, depending on the crystal growth conditions.
The serial nature of a scanning probe microscope (SPM) renders data taking not only slow but may even prevent complex measurement tasks due to time limitations. Here we introduce the concept of compressed sensing (CS) as an effective sampling routine for SPM, requiring a significantly smaller subset of data points without compromising the measured information content. Our approach relies only on the sparsity of information in a vector domain to fulfill the requirements of CS theory. As an example we demonstrate precise reconstruction of the Cu(111) surface state wavevector from a 10-fold undersampled measurement, where the sparsity is given in Fourier space. We expect that our approach will be transformative for laboratories involved in Quantum Point Interference studies.
The ability to resolve individual bonds within a single molecule represents one of the greatest feats of atomic force microscopy (AFM). The imaging mechanism is based on a functionalized tip that dynamically responds to tip-sample interactions. However, these interactions depend on a convolution of sample and tip that puts aspects of the tip's behavior into focus. Here we demonstrate how to trace the orbit of an oscillating AFM-STM tip in three dimensions. We construct the tip-trajectory by applying voltage pulses at varying phases within the oscillation cycle. Lateral shifts in topographic features indicate a skewed oscillation or a dynamical tilting of the functional tip unit. Our method allows to control aspects of AFM imaging and spectroscopy.
The iron pnictides high Tc superconductors exhibit a rich phase diagram that is known for the close proximity of the superconducting (SC) and antiferromagnetic (AF) or commensurate spin-density-wave (SDW) orders. In the hole-doped Ba1-xNaxFe2As2 (BNFA) SDW develops a long-range order that competes with superconductivity and is accompanied by transitions between various structural and magnetic orders (like orthorhombic AF (o-AF) and tetragonal AF (t-AF)).
In this study we present IR reflectivity data together with respective optical conductivity spectra on BNFA compound in the range of dopings where both o-AF and t-AF states live together with superconductivity. Fitting the real part of optical conductivity spectra allows us to describe quantitatively the relation between magnetism and superconductivity in the BNFA samples.
Crystal phase engineering in semiconductors has attracted considerable interest because of its potential applications in solid state lighting and group IV emitters. However, synthesizing materials in their thermodynamically less stable phase is challenging and so far, has mainly been realized in nanowires. Here, we present a general approach to controllably integrate both zinc-blende (ZB) and wurtzite (WZ) phases of III-V semiconductors in a catalyst-free epitaxy yielding large area substrates with exceptionally high material quality. We conduct comprehensive material analysis including HRTEM, PL and CL characterization and find phase purities of 100% and 97% for ZB and WZ InP, respectively.
We study the generic dynamics of a special class of integrable periodically modulated quantum systems. Using conformal field theory and in particular a mapping to sine-square deformed field theories, we analytically obtain the full Floquet dynamics of a large class of conformal field theories. These integrable systems show both heating and non-heating phases. In our work, we explore the correlation between heating and the dynamical behaviour of excitations. We show that the excitations of the system propagate along light cones in curved space-time. This propagation serves to underpin the dynamical processes which lead to heating via an abrupt change in the dynamics. Our work uncovers unexpected rich physics present in integrable Floquet systems.
Particle size dependence of Tc and Hc in nanocrystalline (2-60 nm) BCC Tantalum was measured from electrical transport under magnetic field down to 50 mK. Both parameters show unexpected non-monotonic size dependence. Also, superconductivity is observed to persist for particle size even below the conventional estimate of Anderson limit. Again, when isolated Fe implants are embedded in Ta with particle size below 8 nm, a stable magnetic moment is observed (using the time differential perturbed angular distribution technique), whereas none is observed for larger particle sizes or BCT-Ta (β-Ta) films. The observations are explained using ab initio calculations indicating both effects are related to the strong size-dependent lattice expansion (~4%) in Ta, which influences the electronic and phonon band structure.
In recent years it has been shown that electric fields in solids can be imaged, with sub-atomic resolution, using scanning transmission electron microscopy (STEM) and differential phase contrast imaging techniques. Here we use a Pauli equation based multislice method [Phys. Rev. Lett. 116, 127203 (2016)] to investigate the possibilities of imaging also microscopic magnetic fields with such STEM techniques. Considering an example of a hard ferromagnetic material FePt, We illustrate how sub-atomic resolution images of the microscopic magnetic fields can be extracted for thin samples and suitable electron beam conditions. We discuss related possibilities and limitations, and aspects regarding data interpretation.
Biologically-inspired computation schemes are more effective than standard digital-based approaches when dealing with complex, unstructured tasks as image recognition. In particular, systems of frequency-locked, coupled oscillators exhibit associative memory capabilities encoded in the phase difference of the signal. We are using oscillating neural networks as hardware accelerators for image recognition. In this work, nanometer scale relaxation oscillators are built using the insulator-metal transition of VO2. Our experiments show that the relative phase of coupled oscillators can be configured with the tuning of the coupling strength, i.e. the magnitude of the coupling resistor. This offers the perspective of realization a compact, computational network of oscillators. Mathematical simulations prove the computing capabilities of these networks when scaled to larger sizes.
The fast modulation characteristics of quantum cascade lasers (QCLs) up to the MHz-/GHz-range give insight into their dynamical properties and act as a prerequisite for QCL-based experiments like e.g. the injection locking of mid-infrared frequency combs, spectroscopic measurements or high data transmission optical free-space telecommunication applications. In this paper we present the first analysis of the optical high-frequency modulation characteristics of surface-emitting mid-IR DFB-ring QCLs up to 160 MHz. We compare them to DFB-ridge QCLs from the same gain material and show the existence of the (quasi) single-sideband ((q)SSB) regime, a special FM-state in QCLs, not present in regular diode lasers.
Surface-emitting ring-QCLs are particularly relevant, since they show significant potential in array integration and monolithic (ring-in-ring) laser-detector schemes.
We present a homogeneous, bound-to-continuum Quantum Cascade Laser (QCL) featuring a spectral bandwidth up to 1.65 THz centered at 3.45 THz in a bi-stable CW lasing point above the typically not accessible NDR regime due to voltage driven operation. Below the NDR a spectral coverage of ~1 THz is observed with an electrically detected single and narrow beatnote indicating frequency comb emission. Further, injection locking to an external RF synthesizer with powers down to roughly -55 dBm at the QCL was realized. For increasing injection power the locking range follows the prediction of the Adler's Equation. Therefore, the device features the advantages of low injection powers and low threshold current density, 115 A/cm^2, but bandwidths still comparable to heterogeneous devices.
Terahertz quantum cascade lasers based on double metal waveguides are compact sources of terahertz radiation with excellent properties in terms of covering a large bandwidth and exhibiting low waveguide dispersion. However, as the optical mode is confined to subwavelength dimensions, the emitted radiation produces a highly divergent far-field pattern. We designed and fabricated an antipodal Vivaldi antenna which adiabatically expands the optical mode while rotating its polarization from vertical towards horizontal polarization. Numerical simulations predict a single-lobed far-field pattern with a beam width of less than 20°, spanning over two octaves in frequency (1.5-4.5 THz). Far-field measurements agree well with simulations.
Boron-containing III-V alloys have net yet been thoroughly characterized. Yet, the small lattice-constant of BAs enables applications in strain-engineering of nanowires. We report on the incorporation of B into self-catalyzed nanowires, grown by molecular beam epitaxy. Energy-dispersive X-ray spectroscopy scans in a scanning transmission electron microscope revealed a segregation of B atoms to the nanowire sidewalls, causing inverse pyramidal voids. Electrical measurements on harvested nanowires revealed a p-type conductivity due to anti-site incorporation of B. A rate equation-based model allowed to extract a reduced surface diffusion length at the order of 1000 nm for Ga-adatoms on B:GaAs nanowire sidewalls.
A method for obtaining the dispersion of terahertz (THz) quantum cascade lasers (QCL) is presented. Previously shown in the mid-infrared (MIR) range, it involves measuring the relative phase of the center burst (0th order harmonic peak) and first satellite (1st order harmonic peak) from the interferogram of a THz QCL cavity, operated below threshold, emitting inside a Fourier Transform Infrared Spectrometer (FTIR). The electroluminescence spectrum is thus determined by performing Fourier Transform on the acquired signal and the group velocity dispersion can then be calculated. This method is applicable to any QCL – here shown for Fabry-Pérot (FP) ridge laser as well as vertical external-cavity surface-emitting laser (VECSEL) THz metasurface.
Underdoped cuprate high TC superconductors have been intensively studied, especially since the discovery of the pseudogap phenomenon in the 1990’s [1]. An important step towards the identification of the HTSC pairing mechanism was the discovery of a charge density wave (CDW) existing in large parts of the underdoped phase diagram [2-5]. In zero magnetic field (B=0) the short-ranged, static CDW is induced by defects, while a long-range CDW can be induced for high B-fields along the c-axis (perpendicular to the CuO2 layers).
Here we aim to search for the origin of this CDW and its relationship with superconductivity (competing or interwined order). We performed reflection experiments from THz-NIR region (50cm-1-6000cm-1) while applying high magnetic fields up to B=30Tesla.
The well-known Q-phase in CeCoIn5 is a rare example of cooperative coexistence of superconducting and magnetic order. For Nd0.05Ce0.95CoIn5, a second magnetic phase is stabilized at zero magnetic field with identical symmetry of Q-phase separated by a quantum critical point [1]. We present studies on 2% and 3.5% Nd-doped CeCoIn5 which interestingly shows that the SDW phase vanishes with increasing magnetic fields before the Q-phase is stabilized. This suggests that the two phases are separated by a disordered magnetic phase for low Nd-doped CeCoIn5, representing for two magnetic instabilities and suggesting different origins of the two phases.
[1] S. Gerber et al, Nature Physics 10, 126 (2014).
CeCoIn5 is an intriguing d-wave superconductor with intertwined orders. A spin density wave exists only inside the superconducting phase [1], implying that superconductivity is an essential ingredient for the magnetic Q-phase. Its origin remain under debate. Since phonons couple to the electronic structure at MHz frequencies [2], ultrasound is suitable to investigate the properties of the Q-phase. Here we investigate the response of elastic constants and attenuation of different modes under rotating magnetic fields.
The ultrasound technique is being developed at the PSI. We present our route to establish the technique using a data acquisition card and digital processing.
[1] M. Kenzelmann et al, Science 321, 186-197 (2008).
[2] T. Watanabe et al, Phys. Rev. B 70, 020506(R) (2004).
NbS2 is a layered substance, which has recently shown great promise for building superconducting devices in the 2D limit [1,2]. While the layers consist of covalently bound atoms, weak van der Waals forces hold the layers together. NbS2 crystallises in two stable polymorphs, depending on the sulfur pressure during synthesis: the superconducting 2H phase and the metallic 3R phase[3–5].
We have in a systematic approach analysed this sensitive sulfur-pressure system by modifying the amount of sulfur and the temperature in the synthesis conditions. Based on the results, we established a phase diagram for the given synthesis conditions.
The here obtained synthesis parameters allow for an improved control of the phase purity and phase formation in the NbS2 system.
The Poster Session is held on Wed 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 Wed.
TaAs has been predicted to be a Weyl semimetal with a complex Fermi surface composed of two Weyl and one trivial hole pocket. It is not evident how to describe the low energy excitations. In order to reveal the details of the low energy electronic band structures of TaAs, we performed reflectivity measurements at zero field at various temperatures, as well as magneto-optical spectroscopy up to 34 Tesla at low temperature in the far and mid infrared regions. In a finite magnetic field, Landau level transitions dominate the optical spectra. As the character of the electronic bands determines the splitting of these Landau levels in field, the field dependence of the transitions reveals the electronic ground state of TaAs.
3D Dirac and Weyl semimetals are the analogs of graphene which possess 3D linear dispersion around points in the Brilloun zone. Optical and transport studies are widely used in order to explore these compound. TaIrTe$_4$ is expected to be a Weyl semimetals that have the fewest Weyl points - 4 - in comparison to TaAs, which contains 12 pairs. It has been theoretically shown that TaIrTe$_4$ hosts type II Weyl cones. This type should appear when electron and hole pockets touch in one conical point. Electronic transport in magnetic field allows to identify effective masses, number of carriers and position of Fermi level with respect to the Weyl points. These measurements are complemented by optical conductivity of TaIrTe$_4$.
The Bilinear-Biquadratic spin-1 chain (BLBQ) has been studied for its entangled ground states, diverse phases and topological properties. The natural language to study entanglement in strongly correlated systems is tensor networks. Using time dependent tensor network simulations, we demonstrate the dynamical spin and quadrupolar structure factors of the BLBQ model in ferroquadrupolar dimer phase and antiferroquadrupolar semi-ordered phase and compare them with the ones obtained from the analytical calculations using multi-boson approach. Interestingly, the system is analytically solvable for few points (Takhtajan Babujan, Uimin Lai Sutherland, Affleck Kennedy Lieb Tasaki points). We explore the analogy of the Biquadratic model in dimer phase with spin-1/2 XXZ model using Temperley Lieb Algebra and confirm it via structure factor plots obtained from simulations.
Suspended Bernal-stacked graphene multilayers exhibit a broken-symmetry ground state whose origin remains to be understood. Based on electrical transport measurements, we observe a second-order phase transition, whose critical temperature ($T_C$) increases a function of the thickness of the system, starting from 12K in bilayer up to 100K in heptalayer devices. Furthermore, by means of a phenomenological model, we attribute this transition to the incursion of a self-consistent valley- and spin-dependent staggered potential $\Delta(T)$ that changes sign from one layer to the next.
Our experimental observation of such finite-temperature phase transition imposes additional constraints to the any microscopic theory which attempts to describe electronic correlations on these multilayer graphene systems.
Crystal defects in topological insulators (TIs) are known to bind anomalous electronic states with two fewer dimensions than the bulk; the most commonly cited examples are the helical modes bound to screw dislocations in weak TIs. In this talk, we extend the classification of topological electronic defect states. By mapping the Hamiltonians of planes in momentum space to the real-space surfaces between screw or edge dislocations with integer Burgers vectors, we show that these crystalline defects can bind higher-order end states with fractional charge. We support our findings with extensive numerical calculations. Using density functional theory, we demonstrate the presence of first-order 0D defect states in PbTe monolayers, and HEND states in 3D SnTe crystals.
We investigate and compare few-particle one-dimensional bosonic and fermionic gases with infi?nite-range interactions induced by a laser-driven dissipative optical cavity by computing density distributions and correlation functions. With increasing cavity-atom coupling, both types of gases self-organize into a one-dimensional lattice structure with diff?erent site occupations. As the cavity-mediated light-matter interactions are increased further, the bosons progressively occupy the outer lattice sites and eventually completely localize into highly-correlated single-particle states. At this stage, the correlation functions and density fluctuations of the bosonic gas are indistinguishable from the fermionic ones. We comment on the interplay between contact and cavity-mediated interaction on the emergence of fermionization. Finally, we suggest experimental regimes where our theoretical ?findings could be tested.
Deterministic control of the intrinsic polarisation state of ferroelectric thin films is essential for devises applications. Additionally to the now well-established role of electrostatic boundary condition and epitaxial strain, we show also the importance of Pb-O divacancy gradients. We report on the full control of the polarisation orientation of ferroelectric thin films through changes in the growth temperature and electrical boundary conditions. Using piezo-force microscopy, x-ray diffraction and transmission electron microscopy, we investigated PbTiO3 ultrathin films, PbTiO3/SrTiO3 superlattices and PbTiO3-SrTiO3 solid solution in thin film form, and showed how to fully control their intrinsic polarisation state by tuning the electrostatic boundary conditions and the divacancy dipole gradients.
Nodal-line semimetals offer a unique setting for novel transport phenomena. With weak disorder, the torus-shaped Fermi surface and encircled π Berry flux carried by the nodal loop generate a fascinating interplay between the effective dimensionality of electron diffusion and band topology, which depends on the scattering range of the impurity potential relative to the size of the nodal loop. For a short-range impurity potential, backscattering is dominated by the interference paths that do not encircle the nodal loop, yielding a 3D weak localization effect. In contrast, for long-ranged impurities, diffusion occurs in effective 2D planes and backscattering is dominated by interference paths that encircle the nodal loop, leading to weak antilocalization with a 2D scaling law.
CaAlSi and SrAlSi are ternary superconductors that crystallize in AlB2-type structures with critical temperatures of Tc = 8 K, and 5 K, respectively. They surprisingly differ in properties among each other although they have similar electronic structures, and only a small difference in their crystallographic structures. We have in a systematic approach analyzed the Ca1-xSrxAlSi solid solution and its evolution of the electronic and structural properties. We find that the superconductivity in this system is closely connected to the appearance of the structural distortion of the [AlSi]62- layers. Based on our results we establish the electronic phase diagram and compare it to the one of MgB2.
We report on the synthesis and the superconductivity of the h-carbide type oxides Zr4Rh2Ox (x = 0.7, 1.0). Detail physical measurements show that they are strongly type-II bulk superconductors with critical temperatures of Tc ≈ 2.8 K and 4.7 K in the resistivity, respectively. Our results support that the h-carbide compounds are a versatile family of compounds for the investigation of the interplay of interstitial doping on physical properties in cage-structured compounds, especially for superconductivity.
The Poster Session is held on Wed 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 Wed.
Atomic parity violation experiments are one attempt to look for physics beyond the standard model. An
experiment to measure the atomic parity violation electric dipole contribution to the energy transition 7S1/2
and 6D3/2 in singly ionised Radium-226 is currently ongoing. The extraction of the atomic parity violating
signature for the measurement requires precise calculations based on quantities like the indeterminate radius
of Radium-226. Muonic atom spectroscopy at PSI enables a precise nuclear charge radius determination.
Previous muonic atom spectroscopy experiments at PSI were designed for targets containing at least several
grams. Current safety regulations permit only an amount of a few μg of Radium-226. In this contribution,
newly developed techniques and preparations for low amount targets will be presented.
Ultracold neutrons (UCN) with energies below 300 neV are storable for hundreds of seconds due to total reflection on the effective optical wall potential of the containment. They are used in experiments that benefit greatly from long measurement times, like the search for a permanent electric dipole moment of the neutron. The PSI UCN source makes use of solid deuterium as superthermal moderator to produce UCN. Increasing UCN extraction from the moderator poses a big challenge. We study the impact of structural features in the deuterium on UCN extraction by dedicated energy-dependent measurements and detailed simulations. This will provide important insights helping to further increase the UCN output of the PSI UCN source.
The Beryllium isotopic composition in cosmic rays provides essential information for the study of the propagation of cosmic rays in the Galaxy. The Alpha Magnetic Spectrometer (AMS) installed on the International Space Station (ISS) since May 2011 provides the opportunity to measure this composition in the energy range from ~0.2 GeV/n to ~10 GeV/n with unprecedented precision. For events selected with a specific nuclear charge, the particle mass is obtained combining the velocity measured by the Time of Flight (ToF) or by the Ring Imaging Cherenkov (RICH) detectors with the rigidity measured by the silicon tracker. A method to extract the relative isotopic abundances from the mass distribution will be presented.
Magnesium nuclei in cosmic rays are primary particles thought to be mainly produced and accelerated in astrophysical sources. Knowledge of the precise behavior of the Magnesium spectrum is important in understanding the origin, acceleration, and propagation of cosmic rays.
I will present the precision measurement of the Magnesium flux in the rigidity range from 3 GV to 3 TV based on data collected by AMS-02 during the first 7 years of operation on the International Space Station.
Understanding the precise rigidity dependence of the Silicon flux sheds light on the origin, acceleration and propagation of cosmic rays. I will present the precision measurement of the Silicon flux based on data collected by the Alpha Magnetic Spectrometer (AMS-02) during its first 7 years of operation on the International Space Station.
Muonic atom spectroscopy allows for a precise investigation of nuclear properties. At PSI we want to extract the nuclear charge radius of Radium-226 from its muonic x-ray spectrum. To measure the spectrum using only few µg of Radium-226 we have developed an apparatus in which the muons are stopped in a H2/D2 gas mixture and then diffuse towards a disk containing the Radium-226 nuclei. Monte Carlo simulations of the diffusion are used to optimise the cell so that a large fraction of muons reach the target disk. This poster illustrates the simulated physics and the interplay of simulation and measurement.
The DARWIN Time Projection Chamber will be the most sensitive dark matter detector. The increased size of the detector over its precursors will raise new challenges. The DARWIN demonstrator, designed and to be built at the University of Zürich, will mainly be used to investigate the drift of electrons in liquid xenon over a distance of 2.6m, along with all the technological advances needed to achieve this goal. Amongst others, the design of a high voltage electric feedthrough in liquid phase and the determination of the requirements in xenon purity will be addressed.
DARWIN is a proposed next-generation xenon observatory that will be sensitive, among other rare interactions, to the neutrinoless double beta decay of 136Xe. Future experiments looking for this process will become more and more sensitive while the intrinsic radioactivity of the detector materials will be reduced thanks to the screening campaigns. This brings the risk that backgrounds previously considered negligible become important contributions. In this context, the cosmogenic production of 137Xe by the neutron capture of 136Xe can be relevant if our detector is not sitting at the enough depth. Simulations of muon-induced neutrons with Geant4 allow us to evaluate the production rate of 137Xe and its importance for these searches with DARWIN.
For the neutron Beam EDM experiment at the University of Bern, a dedicated neutron detector has been supplied by the company CDT. The detector has been amply characterized in various aspects by taking data at the beamlines BOA and SANS-1at the Paul Scherrer Institute in September and December 2018. The results of these measurements in terms of efficiency, homogeneity, as well as wavelength and voltage dependency will be presented. Additionally, the implications of the obtained detector characteristics on the experiment are discussed.
Lepton Flavour Universality (LFU) is one of the fundamental properties of the Standard Model: photon, W and Z bosons are predicted to be equally coupled to the three lepton generations. Hints for possible deviations from LFU have been found by the LHCb collaboration in $b\to s \ell \ell$ and $b\to c\ell\nu$ decays, sparking great interest.This poster explains the strategy adopted to study $b\to s\ell\ell$ decays, concentrating on the experimental challenge of estimating the efficiencies. This is a key ingredient to evaluate the ratio between $B\to X \ell \ell$ branching fractions (where $X$ indicate a generic system containing a strange meson and $\ell =e,\mu$), a clean experimental observable sensitive to presence of LFU-breaking new particles.
RADEM is a radiation monitor developed for ESA JUICE mission to icy moon of Jupiter: Ganymede, Callisto and Europa. Instrument contains of set of detectors optimized to measure electrons, protons, heavy ions and angular distributions of incoming radiation.
Assembling and qualification of Si-diode sensors for RADEM as well as test campaign of its Engineering Model were carried out at PSI. Various measurements successfully confirmed quality of the sensors in accordance to mission requirements. EM instrument was exposed to different radiation types at PSI exposure facilities. Detectors were tested with electrons and protons at different energies and fluxes.
Detailed Monte Carlo simulations and modelling runs were started to verify instrument responses and provide calibration factors for spectra unfolding algorithms.
The XENONnT experiment, projected to begin operation by early 2020 at the Laboratori Nazionali del Gran Sasso (LNGS), is a double-phase Time Projection Chamber with a 6 tonne liquid xenon target. Primarily developed to detect Weakly Interactive Massive Particles (WIMPs) that scatter of xenon nuclei, it will also be sensitive to neutrinos coming from a supernova burst beyond the edge of the Milky Way. Given its low background rate and neutrino flavour blindness of coherent elastic neutrino scatterings (CEvNS), XENONnT will be able detect supernova (SN) neutrino bursts in real-time. We describe the framework to run an active SN trigger using XENONnT’s open-source processor (Strax), based on the continual counting of proportional scintillation signals (S2) induced by such SN neutrinos.
XENONnT, the next stage in the XENON collaboration's search for dark matter, ist is an evolution of the very successful XENON1T experiment, which has set the strongest limits on various channels of WIMP-nucleus interactions and observed double-electron capture in $^{124}$Xe for the first time. A larger detector will mean a much-increased exposure and better self-shielding, giving sensitivity to smaller dark matter interaction cross-sections. Innovations in xenon handling will allow a substantial background reduction, with in particular the $^{222}$Rn background being roughly ten times lower. Furthermore, a new neutron veto can tag at least 80% of singly-scattered neutrons, which until now formed an almost irreducible background. XENONnT is currently under construction with commissioning planned to start at the end of 2019.
Antihydrogen studies aim to shed light on the observed baryon/antibaryon asymmetry in the Universe by comparing the properties of matter and antimatter with very high precision. In the context of the GBAR experiment located at CERN, our aim is to perform a measurement of the antihydrogen Lamb shift with an uncertainty of 100 ppm, which allows extracting the antiproton charge radius at a level of 10%. Due to the two years shutdown of the accelerator complex at CERN, no experiments with antihydrogen can be performed until 2021. In the meantime, the setup is being tested and optimized by using the same detection method with a hydrogen beam at ETH Zurich. The experimental setup and the current status will be presented.
The SHiP experiment is a beam dump experiment proposed at the CERN SPS aiming at the observation of long lived particles very weakly coupled with matter and at the study of tau-neutrino properties. Hidden particles are mostly produced in the decay of charmed hadrons and tau neutrinos are produced by Ds decays, therefore measuring charm production cross-sections from 400 GeV protons is critical for the SHiP experiment. This poster will report on the dedicated experiment proposed to measure different characteristics of charmed hadronic production in a SHiP-like target and on the ongoing analysis of the optimization run which was conducted in July 2018.
NoMoS, the neutron decay products momentum spectrometer, investigates
the beta decay of the free neutron. It uses the R×B drift effect in a uniformly
curved magnetic field and a spatially resolving detector to separate and measure
the charged decay particles according to their momentum. The protons from
the decay are low energetic and need to be made detectable, therefore require
post-acceleration by a high voltage electrode that surrounds the detector. The
poster shows the preliminary detection system and systematic effects introduced
by the high voltage applied to the detector and the electrode.
The Poster Session is held on Wed 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 Wed.
Cobalt-based layered perovskites have emerged as promising electrocatalysts for the oxygen evolution reaction (OER), but fundamental questions regarding the design principles for highly active perovskite electrocatalysts are still open. A recent study demonstrated that oxygen vacancies play a critical role in the OER mechanism and on the perovskite electrochemical activity.
Double perovskite oxides, such as PrBaCo2O5+x (PBCO), are able to incorporate large amounts of oxygen vacancies with high oxygen mobility. We combine high-resolution neutron and X-ray diffraction, XAS, magnetic and electrochemical analysis to understand the correlation between catalyst activity and oxygen vacancy amount and distribution.
In the past years, magnetism-driven ferroelectricity and gigantic magnetoelectric effects have been reported for a number of frustrated magnets with spiral magnetic orders. Such materials are of high current interest due to their potential for spintronics and low-power magnetoelectric devices. However, their low magnetic order temperatures (typically < 100 K) greatly restrict their fields of application.
Recently, we have established that chemical disorder is a powerful tool that can be used to stabilize magnetic spiral phases up to 310 K [1]. Here we explore the design space opened up by this novel stabilization mechanism, recently rationalized in terms of random magnetic exchanges [2]. We show that in CuFe-based layered perovskites Tspiral can be further increased up to 400 K, and we reveal a scaling law between this quantity and the spiral wave vector [3]. This linear relationship ends at a paramagnetic–collinear–spiral multicritical point, which defines the highest spiral-order temperatures that can be achieved in this kind of materials. Based on our findings, we propose a general set of rules for designing magnetic spirals in layered perovskites using external pressure, chemical substitutions and/or epitaxial strain, which should guide future efforts to engineering spiral phases with order temperatures suitable for technological applications.
[1] M. Morin et al., Nature Communications 7, 13758 (2016)
[2] A. Scaramucci et al., Physical Review X, 8, 011005 (2018)
[3] T. Shang et al., Science Advances, 4, eaau6386 (2018)
Spin-rotation coupling is an extension of the Sagnac effect, based upon the inertia of intrinsic spin. To confirm its existence, a neutron interferometer experiment was proposed [1,2] coupling the spin to the rotation of a magnetic field. The results of a neutron polarimeter experiment comply with the prediction but can also be explained semi-classically.
A spin manipulator for a respective interferometer experiment is developed [3] which produces a rotating field while ensuring a non-adiabatic transition, necessary to induce Larmor precession. The observed phase shift of interferograms [4] is linearly dependent on the frequency of the rotating field. This result is purely quantum mechanical.
[1] B. Mashhoon, Neutron interferometry in a rotating frame of reference, Phys. Rev. Lett. 61, 2639 (1988)
[2] B. Mashhoon and H. Kaiser, Inertia of intrinsic spin, Physica B 385–386, 1381 (2006)
[3] A. Danner et al., Development and perfomance of a miniaturised spin rotator suitable for neutron interferometer experiments, J. Phys. Commun. 3, 035001 (2019)
[4] A. Danner et al., Spin-Rotation Coupling Observed in Neutron Interferometry, arXiv 1904.07085
The Poster Session is held on Wed 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 Wed.
The observation of interference phenomena in two-dimensional mesoscopic systems is difficult, and so far constrained to graphene, where certain mechanisms originating in the graphene band structure strengthen the emergence of this phenomenon. Here, we report on the experimental observation of Fabry-Pérot oscillations in electrostatically defined cavities in InAs/GaSb quantum wells. Carriers travelling through the cavity are reflected at the interfaces, leading to interference. The emergence of the interference is a consequence of the band inversion and electron-hole hybridization. Our work expands the field of electron optics to a rich class of two-dimensional systems with tunable band structure.
The last decades have seen significant advances in coherence times of superconducting qubits. This was mainly made possible by reducing charge dispersion of transmon qubits, better thermalization and filtering of the readout and control circuitry as well as improvements in Josephson junction fabrication. Lately, efforts are being made in order to investigate limitations of coherence due to material interfaces and two level fluctuators [1-3].
Here we present our work towards understanding decoherence mechanisms in transmon qubits via surface treatments and sample packaging. We show qubit packaging under UHV or a controlled atmosphere, study surface treatments and discuss coherence data from measured devices.
[1]J.M.Gambetta, et al., IEEE Trans.Appl.Supercond., 27, (2016).
[2]S.DeGraaf et al., Nat.Communications 9, (2017)
[3]C.Müller et al., arXiv:1705.01108 (2017)
Fast and accurate two-qubit gates are a key requirement to perform complex algorithms on current quantum computers. Typical gates have errors less than 5% and take around 200ns. Shorter gates result in unwanted leakage out of the computational subspace. Optimal control theory aims to design fast control pulses that suppress side effects such as cross talk and leakage. However, even with an accurately calibrated system model, control pulses require a tune-up to accommodate for parameter drifts and model inaccuracies. Here, we present our work on methods to simultaneously calibrate control pulses defined by up to 20 parameters. We improve the interplay between the control instruments and the multidimensional optimization algorithms to reduce the hardware constraints to realize efficient tune-up feedback-loops.
This poster studies the entanglement of two and three spin 1/2 particles in (special) relativistic settings, in particular for inertial observers at rest relatively to the entangled particles and in a Lorentz-boosted frame.
Here spin and momentum degrees of freedom of the particles can be viewed as 4-qubit and 6-qubit states, respectively. These states are analysed in terms of their entanglement properties, i.e. how the entanglement is affected for a Lorentz-boosted observer. It turns out that there are partitions for which the entanglement is invariant, for others the opposite is true. Also the effect of Lorentz-boosts on Bell-inequalities is investigated.
The oscillation of neutrinos was predicted in the mid of the last century. Since then they were intensively studied both theoretically and experimentally since a couple of phenomena like e.g CP violation (charge-conjugation-parity) are conjectured. Also, it is not known which neutrino is the heaviest, formulated as the mass hierarchy problem. I will focus on how tools from foundations of quantum mechanics can give answers to these riddles in neutrino physics. In particular, a type of the Leggett-Garg inequalities, kind of time-like versions of Bell inequalities, will be investigated for neutrinos propagating through matter.
We implement a single electron charge qubit in a gate defined linear triple dot array on a GaAs/AlGaAs heterostructure [1,2]. The qubit is strongly dipole-coupled to photons in a high impedance frequency tunable superconducting resonator. We operate the qubit at a higher order sweet spot along one of the detuning axes. Measuring the qubit coherence for different qubit configurations we acquire information about the dominant noise source in our system.
[1] A. J. Landig et al.,arXiv: 1903.04022 (2019)
[2] J. V. Koski et al, Manuscript in preparation
Distributing a secret to many parties such that none alone can reveal it was first proposed by Shamir (1979) and applied in the quantum scheme by Hillery, Bužek and Berthiaume (1999). By a modification of this HBB protocol Hiesmayr, Huber and Schauer showed that the security against eavesdropping or a dishonest party can be based on the physical property due to entanglement, more precise genuine multipartite entanglement of the Greenberger-Horne-Zeilinger-type. In this poster we extend the protocol to higher dimensional quantum systems, show that they provide more aspects and study its security by inequalities witnessing the specific genuine multipartite entanglement.
We explore theoretically the behavior of two coupled nonlinear photonic cavities, in presence of inhomogeneous coherent driving and local dissipations. By solving numerically the quantum master equation, we extrapolate the properties of the system in a well defined thermodynamical limit of large photon occupation. We focus on the peculiar regime where the mean field Gross-Pitaevskii approach predicts a unique parametrically unstable steady-state solution. Here,the dynamics of the open quantum system exhibits a time cristal behavior characterized by the presence of purely imaginary eigenvalues in the spectrum of the Liouvillian superoperator at the thermodynamical limit.When the amplitude of the inhomogeneous driving is changed,we observe the emergence of two dissipative phase transitions from the time cristal to the fully classical coherent phase.
The recently developed theory of entangled two-photon absorption (ETPA) predicts a linear dependence of its rate on the entangled pair flux in the low-power regime, and provides a tool for two-photon studies even on sensitive samples. We experimentally observed this signature for ETPA-induced fluorescence of Rhodamine 6G and its dependence on inter-photon delay, concentration and polarization to find out which degrees of freedom play a role in ETPA. The developed methods have possible applications in sensing, spectroscopy, imaging and fluorescence microscopy, especially for biological objects in vivo, that could be susceptible to damage from intense laser schemes.
Nanomechanical resonators with high quality factors and noise isolation are promising candidates for pushing the frontiers of magnetic resonance force microscopy towards single-spin detection. Single spin detection using state-of-the-art MRFM is hampered by the intrinsic weakness of the kHz-range signal and its frequency mismatch with the MHz-range resonators used to detect it. An alternate sensing scheme is developed here which uses the normal modes of coupled, parametrically driven oscillators, achieving simultaneous amplification of the signal and its frequency conversion. Furthermore, nonlinear corrections to the model predict critical regimes with striking signal-dependent features in the response function, opening up novel weak-force measurement paradigms. Our sensing scheme can be easily implemented using nanomechanical membranes.
We present the coupling of a trapped ion to a nanomechanical oscillator/nanowire in order to study new methods for the preparation of complex motional quantum states that might be challenging to produce by conventional optical means. The quantum dynamics of such a hybrid system have been studied theoretically showing possibilities of creating coherent states, as well as purely non-classical states such as cat-states and others. Here, we discuss the prospects of this approach and its experimental implementation.
The application of quantum-logic techniques to the spectroscopy of trapped molecular ions has enabled the determination of molecular properties at unprecedented levels of precision. Molecules have been proposed as suitable candidates for testing possible time-variation of fundamental constants and precision testing of QED. Further advancement in the measurement accuracy will be enabled through the implementation of network for the distribution of the Swiss frequency standard. We are currently establishing a complete toolbox for high-precision spectroscopy of single molecules using quantum-logic methods, their initialization, coherent manipulation and non-destructive interrogation by coupling them to a co-trapped single atomic ion. We have laid the experimental and theoretical foundations for hyperfine-state initialization of the molecular ions and addressing the suitable extremely narrow infrared transitions.
Discrete time crystals are a many-body state of matter where time translation symmetry is spontaneously broken in a periodically driven system. In view of the intense debate regarding the minimal requirements for the realization of a discrete time crystal, here we present a very pedagogical example of a many-body time crystal using coupled parametric resonators. We use classical bifurcation theory to study this resonator network and provide a clear distinction between an effective single mode and a truly many body time-translation symmetry breaking. We experimentally demonstrate this paradigm using two coupled mechanical oscillators, thus providing a clear route for time crystals realizations in real materials.
We create exciton-polariton condensates in engineered potential landscapes at room temperature by optically exciting a ladder-type conjugated polymer placed inside a tunable optical microcavity. In the upper mirror of the cavity we define multiple in-plane structures (from single defects to lattices). By exciting the system above threshold, we observe polariton condensation. Condensation features such as non-linear emission and linewidth narrowing are shown. Energy dispersions in k-space as well as temporal and spatial coherence are studied for different states by detuning the cavity. Our results represent a step towards the realization of a polariton simulator at ambient conditions.
We propose a triply-resonant electro-optic modulator as an efficient stationary source of entangled microwave and optical radiation, based on a mm-sized high optical $Q$ lithium niobate whispering gallery mode resonator (WGMR) coupled to a superconducting 3D microwave cavity. The creation of entangled microwave and optical photons is possible via spontaneous parametric down conversion (SPDC) in the lithium niobate WGMR. By profiting from the resonance intensity build-up of the modes, the device can achieve creation rates of $\sim10^6$ entangled bits/s for conservative system parameters at optical pump powers in the order of tens of $\mu$W. Furthermore, the implementation of this device as an Einstein-Podolski-Rosen source in a Braunstein-Kimble teleportation set-up allows quantum state transfer between microwave and optical Gaussian states.
Interfaces between stationary and traveling qubits are fundamental building blocks for quantum networks. Cavities are an established approach for an efficient interface; here, we use a fiber cavity to couple trapped ions to photons. Fiber cavities enable access to the strong coupling regime, allowing quantum communication to be carried out over long distances with high fidelity and efficiency. To couple multiple ions, we have designed an ion-cavity system in which fibers are integrated inside electrodes along the axis of a linear Paul trap. As an intermediate step, we have measured heating rates and micromotion of our trap in the absence of fibers. After reassembling the trap with the fiber cavity, we are currently characterizing the full system.
Integrated photonic sources represent a key building block as practical, low-cost, schemes for quantum communication. In the context of photon pair sources, microring-resonators (MRR) are emerging as a viable solution for integrated photon pair sources with advantages for multiplexing and high dimensional entanglement generation.
By exploiting MRR as a photon pair source, sequential time-bin entanglement is generated with 750 MHz pump rate and interference fringes with raw visibility up to 98%. Detected coincidence counts rate of up to 80 kHz was achieved by relying on low loss commercial telecom filters, and state of the art superconducting single photon detectors. We also present several techniques that we have incorporated to characterise and mitigate noise while improving pump rejection and channel selection.
Solid-state electronic spins are promising candidates for various applications in quantum information science, such as quantum communication and computation. However, due to their strong magnetic dipoles they are quite susceptible to magnetic noise, which usually limits their coherence lifetimes. Here we demonstrate the storage of a 100 ns optical pulse in a 171Yb3+:Y2SO5 paramagnetic crystal for more than 1 millisecond. For this we utilize the microwave and optical clock transitions that are present in this material at zero magnetic field. The large hyperfine splittings make this system promising as a broadband quantum memory, and potentially couple for coupling of spin systems to superconducting qubits.
Exploiting the band-gap induced by perpendicular electric fields, charge carriers in bilayer graphene can be confined via electrostatic gating. This realization provides a versatile and tunable platform hosting carbon-qubits.
We confine charge carriers to a narrow channel, defined by lateral gating. Another layer of gates, perpendicular to the transport direction, locally tune the carrier density in this channel. They serve as either plunger gates or tunnel barriers. A range of coupled multi-dot systems are formed, where the occupation can be tuned to the few-carrier regime in single dots. The tunnel couplings can be varied by more than two orders of magnitude, allowing us to study fully tunable quantum dot arrays of arbitrary polarities and couplings.
The accuracy of time information generated by clocks can be enhanced by allowing them to communicate with each other. Here we consider a basic scenario where a quantum clock receives a low-accuracy time signal as input and ask whether it can generate an output of higher accuracy. We propose protocols that, using a clock with a d-dimensional state space, achieve an accuracy enhancement by a factor d (for large d). If no feedback on the input signal is allowed, this enhancement is temporary. Conversely, with feedback, the enhancement can be retained for longer. The protocols may be used to synchronise clocks in a network and de?fine a time-scale that is more accurate than that achieved by non-interacting clocks.
The truncated classical coupled cluster (CC) methods have been known to provide non-variational energies in the systems that present multiconfigurational nature of the ground state. Methods such as paired CC (pCC) and singlet CC (CC0) unreliably correct this failure by eliminating excitations in the cluster operator.
In this work, we show that their unitary implementation (q-pUCC, q-UCC0) on digital quantum computers (QC) using the variational quantum eigensolver algorithm (VQE) with a single Trotter step unconditionally cures the breakdown of their classical counterparts. In addition, the q-UCC0 reproduces the geometric features of the exact energy landscape more accurately than the quantum pCC (q-pUCC) method.
Moreover, we propose a selection criterion that improves on the existing MP2 amplitude-based selection scheme by eliminating the single excitations which enables the optimiser to recover the correlation energy in less iterations. The robustness of these methods is tested on the H4, H2O, N2 molecules and the repulsive Hubbard model, in a QC simulator, Qiskit, using various qubit and circuit depth reduction schemes which are currently necessary for the implementation on the NISQ hardware.
In our experiment, we inductively couple a mechanical oscillator to a microwave circuit. Our magnetic cantilever leads to a position dependent magnetic field. This field is coupled to a microwave resonator via an embedded SQUID i.e. the resonance frequency depends on flux and consequently on the position of the cantilever.
Our first devices indicate a single photon coupling strength of up to 3 kHz (mechanical frequency around 300 kHz). In the near future, we want to investigate cooling of our mechanical cantilever –- a macroscopic object, eventually reaching the quantum ground state.
We numerically study a weakly-interacting, harmonically-trapped boson gas coupled to a high-finesse optical cavity. The bosons self-organise into a lattice when the driving laser is strong enough. When the cavity is blue-detuned, we observe dimerization of lattice sites which leads to states with different atomic correlations. With an even stronger pumping laser, the system is driven into dynamical instabilities, where strange attractor and chaos are observed. Such instabilities are related to Neimark-Sack bifurcation. However, the strange attractor behaviours are extremely vulnerable in the presence of atomic fluctuations and a tight harmonic trap.
The loss of qubits - the elementary carriers of quantum information - poses one of the fundamental obstacles towards large-scale and fault-tolerant quantum information processors. We demonstrate an experimental toolbox for ion-qubit control and implement a full cycle of qubit-loss detection and correction on a minimal instance of the topological surface code. This includes a quantum non-demolition measurement of a qubit-loss event, triggering an in-circuit conditional code-switching operation. This enables the restoration of encoded logical information by mapping it onto a new quantum correcting code on a reduced number of qubits. Together with techniques to correct computational errors, this constitutes essential building blocks for complete and scalable quantum error correction.
The Poster Session is held on Wed 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 Wed.
The chiral-lattice ferrimagnet Cu2OSeO3 has been evidenced to exhibit a second skyrmion phase stabilized by cubic anisotropy well below 57K. It is particularly interesting when aiming at an experimental investigation of magnon band structures in skyrmion lattices and their potential application for microwave devices operating at GHz frequencies. We explored spin excitations in a Cu2OSeO3 single crystal by broadband GHz spectroscopy by high field cooling down. Beyond modes attributed to the conventional low-temperature helical, conical and ferrimagnetic phases, we observe a further weak resonance at a relatively low frequency of about 1.5 GHz which might hint towards excitation of the second skyrmion phase. The work is supported by SNSF via grant 171003 (sinergia project Nanoskyrmionics).
Due to their promising technological applications, magnetic Skyrmions in Chiral magnets, such as Cu$_2$OSeO$_3$, have been the center of attention of the scientific community. By manipulating the crystallite size in the range of a single Skyrmion (62nm), it could be interesting to see if the magnetic phase diagram can be tuned. We have employed solution growth techniques to have controllable size of nanocrystals varying from 35nm to 300nm. The size-specific magnetic phase diagram of nanoparticles has been explored using DC magnetization, AC-susceptibility and Small Angle Neutron Scattering studies. Our experimental results have been further verified using micro-magnetic simulations. We observe a systematical change in the magnetic phase diagram with the change in particle size.
Skyrmions are topologically protected nanometer-sized magnetic vortices interesting for spintronics applications. Current challenges lie in the discovery and synthesis of materials with high critical temperatures ($T_c$) and their implementation in thin-film technology. Here we present an approach for strain-free epitaxial thin-film growth of near-room temperature skyrmion-hosting material Co$_{10-x}$Zn$_{10-y}$Mn$_{x+y}$. $T_c$ can be systematically tuned beyond room temperature by adjusting Co:Zn:Mn composition. We use graphene grown on Si as an underlying substrate for molecular beam epitaxy. Graphene allows us to exploit van der Waals interaction for strain-free growth. We report on the structural, compositional and magnetic properties of Co$_{10-x}$Zn$_{10-y}$Mn$_{x+y}$ ($1 < x, y < 3$) thin films. This growth technique opens a new route for integrating skyrmionic device concepts with silicon electronics.
The Poster Session is held on Wed 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 Wed.
The functionalizing of downscaled solids by precise engineering of small defects, voids, porous structure and the amount, distribution and connectivity of such is a vibrant field of research and in demand of improved descriptors to successfully discriminate the increasing complexity. Positron Annihilation Spectroscopy (PAS) as a non-destructive method employing the unique sensitivity of the annihilation characteristics of positrons to their immediate electronic environment on the nanometer scale hereby yields complementary insight to established techniques. Acting as a dynamic local probe, positrons are able to resolve the smallest structural features in various depth and concentrations. We present recent breakthroughs in the characterization of hierarchical porous materials and highlight other high-impact applications with PAS.
In this work we present the implementation of a sinusoidal modulation of the magnetic field to a Reflectance Difference Magneto-Optical Kerr Effect (RDMOKE) setup with increased sensitivity that allows detecting variations of the Kerr rotation angle below 1 μrad/mT at applied fields of a few mT. We illustrate the capabilities of the setup for Ni thin films grown on Cu(110)-(2x1)O surfaces that exhibit a sharp spin reorientation transition (SRT) of the magnetic easy axis from in-plane to out-of-plane at a coverage of 9 ML. Additional frequency analysis of the magneto-optic response to the magnetic field reveals new details of the Ni-SRT and demonstrates the potential of the setup for studying ultrathin organic/ferromagnetic interfaces.
Interest in ferroelectric perovskites is due to their applications in electronics, and thin films are especially relevant. However, bulk properties, such as ferroelectricity itself, can be compromised at reduced scale. In this work, ferroelectric lead titanate (PTO) thin films are investigated.
Experimental (second harmonic generation) and computational (density functional theory) methods were employed to study thin films of PTO(100). It was found that the polarization in the film is strongly influenced by the geometric and electronic structure of the surface. A stoichiometric PTO(001) surface has a strongly reduced polarization which can be restored by the deposition of adsorbates [1, 2].
References
[1] D. D. Fong et al., Phys. Rev. Lett., 96:127601 (2006).
[2] M. Stengel, Phys. Rev. B, 84:205432 (2011).
In this project we used X-ray Absorption Spectroscopy,X-ray Linear and Magnetic Circular Dichroism at the Mn $L_{3,2}$-edges to understand the ferromagnetic stability in $La_{0.7}Sr_{0.3}MnO_{3}$(LSMO) when interfaced with $SrRuO_{3}$(SRO),which is absent for the LSMO//$SrTiO_{3}$(STO).It has been proposed that charge transfer at the interface between LSMO and SRO allow the $dx^{2}-y^{2}$ orbital to mediate the in-plane double exchange,which stabilizes the ferromagnetic ordering of LSMO down to 1-2 unit cells.We have probed the orbital anisotropy and magnetism of LSMO in LSMO/SRO bilayers varying thickness of LSMO(2/4/8/15 u.c.) and SRO(3/20 u.c.).Antiferromagnetic coupling of 2 and 4 u.c. LSMO with SRO was observed even below critical thickness of LSMO.LSMO/SRO data shows $d3z^{2}-r^{2}$ preferential occupation below 15 u.c LSMO.Our result is in agreement with theoretical prediction.
In the last years we established a new technology by using an in-house build STM in field emission regime. The emitter source (STM tip) is placed few nanometers away from the sample, where direct tunneling is suppressed. A part of the primary beam is backscattered (elastic and inelastic) from the sample and can escape the tip-target junction. The spin polarization of these electrons, which is a fingerprint of the surface magnetization, is analyzed with a Mott detector. We develop a new low-temperature STM (4 K) not only to increase the stability of the experiment and to reduce noise but also to be able to study fundamental spin structures.
The electronic properties of a hexagonal Boron Nitride (h-BN) monolayer on Pt(110) were investigated by ARUPS and compared to DFT-calculations. A work function change of about
-0.74 eV between the h-BN covered Pt(110) surface compared to pristine Pt(110) indicates a net charge transfer from h-BN to Pt. The measured electronic band structure is similar to previously reported band dispersions of h-BN monolayers on transition metals (e.g. Pd(111)[1]) as expected for a weakly interacting adlayer. Due to the (1x5) missing-row-reconstruction of the h-BN/Pt(110) surface, additional umklapp bands in the dispersion plot can be found, which have not been reported on Pt(110) yet [2].
[1] Morscher et al. Surf. Sci. 600 (2006) 3280–4
[2] Achilli et al. Nanotechnology 29 (2018) 485201
The interface effects in cuprate/manganite multilayers are the subject of many studies, which are focused not only on superconducting properties of antagonistic YBa2Cu3O7(YBCO), but also on its magnetic and electronic properties. In this study we will present our last investigations that proved that in Nd1-x(Ca1-ySry)xMnO3/YBCO/NCSMO (NYN) trilayers, the interfacial electron transfer and the orbital reconstruction of the interfacial Cu ions depend significantly on hole doping x, tolerance factor (strontium ratio y), and the subsequent charge/orbital order of the manganite. This interface phenomena can potentially lead to combined superconducting/charge-ordered quantum states in YBCO that can be adjusted via manganite layers and external control parameters like magnetic field or photons, which is an exciting prospect for future technologies.
With the aim of improving detection and analysis of Low-Energy and Secondary Electrons (LEEs and SEs of ≤100eV) in the Scanning Field-Emission Microscope (SFEM) tests are performed on a miniature electron detection unit employing a Bessel Box energy analyser. In electron microscopes, detection of LEEs is inherently difficult due to the presence of electrostatic (and magnetic) fields in proximity of the beam-target interaction region, inhibiting the escape of SEs and complicating the interpretation of their detected signal. The reduced dimensions of such a compact energy analyser (length of 1&1/2 channeltrons) consents its employment close to the sample surface, thus minimising the aforementioned fields effects. Experimental results demonstrating the capability of this analyser to collect electron spectra are discussed.
The tangled processes involved in electron-induced Secondary Electron Emission (SEE), responsible for the generation of the ubiquitous Secondary Electrons in a solid surface, are discussed. The interaction of Low-Energy (LE) Electrons with diverse surfaces, of varying long-range order, was investigated by combining measurements of the Total Electron Yield, single-electron as well as (e,2e)-coincidence spectroscopies. The elementary processes relevant for the understanding of SE-generation probability are identified and fully take into account both conservation laws in the collision and the band structure of the solid. Single ionising scattering events, assisted by collective excitations, i.e. plasmons, constitute one of the fundamental ingredients leading to SEE. In the LE-regime the electron yield of a material is strongly dictated by the target band structure.
A new solvent, formic acid, was used to fabricate sericin films. The effects of formic acid on the structural characteristics and mechanical properties of the sericin films were examined and compared with water. The gelation of sericin solution was retarded in formic acid compared to that of water. Sericin films cast from the formic acid exhibited a much higher crystallinity index than that produced from water. The tensile strength and elongation of the sericin films cast from the formic acid solution were more than double that of the sericin films cast from water. It is expected that high-crystallinity sericin films, which have significantly improved mechanical properties, produced by using formic acid could be utilized in biomedical and cosmetic applications
Electronic spins yield excellent sensors which enable quantitative, nanoscale imaging even down to the level of single spins. I will describe the basic working principles and technological achievements of such quantum sensors and highlight some of their recent scientific applications to open questions in condensed matter physics.
Specifically, I will discuss how we employ single electronic spins in diamond for nanoscale probing of antiferromagnetic systems and high-resolution imaging of atomically thin “van der Waals” magnets. For both, the combination of sensitivity, spatial resolution and quantitative imaging enables unprecedented insights such as quantitative, in-situ determination of magnetic moment densities or the imaging of nanoscale domains.
I will conclude with an outlook of future developments of single spin magnetometers for extreme conditions, such as high magnetic fields, millikelvin temperatures or for high-frequency sensors to probe the dynamics of nanomagnetic systems.
Optical wavefront shaping with spatial light modulators (SLMs), such as deformable mirrors, digital micro-mirror devices or liquid crystal (LC) panels, has become a powerful tool in Biophotonics. “Holographic optical tweezers” are well-known and widespread, but an SLM can also be integrated into optical imaging systems, making the microscope programmable and adaptable with respect to the needs of specific samples. A particular strength of the approach with programmable phase masks is the possibility to multiplex, which means that one can ‘pack’ several tasks into one computer-generated hologram. Wavefront shaping with SLMs also enables targeting structures for optogenetical stimulation of neurons in 3D, or imaging into deeper depth in scattering media.
The Advanced Wakefield Experiment, AWAKE, is an accelerator R&D experiment at CERN using for the first time ever a high-energy proton bunch to drive plasma wakefields in plasma and accelerating electrons to the GeV energy scale and, in the future, takes advantage of the large energy store in the proton bunch to reach very high energy gain in a single plasma.
The principle of the AWAKE experiment is described. We show the experimental results of the seeded self-modulation process of the long 400 GeV/c SPS proton bunch transforming the bunch into a train of bunchlets and driving resonantly the wakefields in the 10 m long Rb plasma. We also show the acceleration results to several GeVs of electrons that have been externally injected into these wakefields.
In addition the next steps of the AWAKE experimental program as well as first possible applications of this acceleration scheme will be described.
Polaritons are half-light half matter quasiparticles resulting from the strong coupling of photons confined in a microcavity with excitons confined in a semiconductor quantum well. Polariton condensates may be created both spontaneously through a “standard” phase transition towards a Bose-Einstein condensate, or be resonantly driven with a well-defined initial phase, speed and spatial distribution.
Thanks to the photonic component of polaritons, the properties of the quantum fluid may be accessed very directly, with in particular the possibility of detailed interferometric studies. This allows for example to probe the long-range coherence properties of a quantum fluid with unprecedented ease. This also allows testing superfluid properties with great precision in space and time.
In this talk, I will review the main achievements in the field of polariton physics, and try to give some perspective for future research tracks. I will show that polaritons are benefiting, through their photonic component, from a very small mass, and at the same time, through their matter component, they are able to interact. The consequences of this double nature are manyfold.
The Poster Session is held on Wed 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 Wed.
Despite the tremendous success of the Standard Model of particle physics, there remain several fundamental aspects of the Universe that are still not understood. One such is the violation of the symmetry of simultaneous charge exchange and parity inversion (CP), which allowed the early Universe to become more abundant in matter than in antimatter. For some 65 years the electric dipole moment of the neutron (nEDM) has been giving an increasing insight into this problem.
An nEDM measurement at the Paul Scherrer Institute in Switzerland has finished taking data with enough statistics to go beyond the present limit standing at 3 × 10-26 ecm (90% C.L.) [1]. In my talk I will explain how we measured the nEDM using the Ramsey interferometry of neutrons. Operating at neV energies, we employed an exciting combination of the gravitational, strong and electromagnetic interactions to guide, store and manipulate the spins of polarised ultracold neutrons. The measurement required magnetic field stabilities on a picotesla level, reaching of which was only possible thanks to an active magnetic field compensation system. I will speak about how it works and, in particular, how we design ten-metre-large colis for that system [2]. Finally, I will show how we could use our measurement for an entirely different purpose: a search for an ultra-low-mass axion dark matter [3].
[1] C. Abel et al. https://arxiv.org/abs/1811.04012 (2018)
[2] M. Rawlik et al. Am. J. Phys. 86, 602 (2018)
[3] C. Abel et al. Phys. Rev. X 7, 041034 (2017)
The XENON project aims to directly detect Dark Matter, employing a dual-phase TPC (Time Projection Chamber) with a xenon target. Located at the Gran Sasso National Laboratory (LNGS), the XENON project began in 2006 with the prototype XENON10, followed by XENON100 in 2008. The third phase, XENON1T, has already achieved the highest sensitivity to the elastic scattering of nucleons and WIMPs (weakly interactive massive particles). Most recently, following an exposure of 1.0 tonne$\times$years, XENON1T has set the strongest limits on WIMP-nucleon spin-independent elastic scattering cross section for WIMP masses above 6 GeV, with a minimum of $4.1\times10^{-47}cm^2$ at 30 GeV/$c^2$ and 90\% confidence level. In addition to this benchmark WIMP search, the results of complementary physics channels will be reported.
The XENON1T dark matter experiment, located at the Laboratori Nazionali del Gran Sasso, currently holds the world-leading limit for direct detection of Weakly Interacting Massive Particles. Due to unprecedented low backgrounds, it also has discovery potential to dark matter in the form of dark photons and axion-like particles via absorption by bound electrons. Here I will present the latest results in the search for dark absorption from a 220-day science run of XENON1T.
The XENON1T experiment searches for Weakly Interacting Massive Particle (WIMP) dark matter candidate with a dual-phase xenon time projection chamber. Following the main result on spin-independent WIMP-nucleon scattering, the effort of the XENON collaboration is directed towards exploring other detection channels. For this purpose the signal reconstruction and data analysis need to be extended up to the MeV energy range, two order of magnitude higher than the standard WIMP analysis. This would allow in particular to perform the analysis on the 136Xe neutrinoless double beta decay, fundamental to prove the Majorana nature and solve the hierarchy problem of the neutrinos. The current achievements and ongoing work aimed to explore the high energies detection channels will be presented.
The current best estimate for the universe’s matter content consists of 84% dark matter, and the search for its composition remains of great interest. One possible candidate is a so far undetected ultra-low-mass axion. Various astronomical observations, and only one laboratory experiment, using ultra-cold neutrons, currently constrain the axion mass and its interaction strength in the allowed phase space. In this talk, the idea of a new complementary laboratory search for an axion-induced oscillating neutron electric dipole moment using a cold neutron beam Ramsey setup will be presented.
The SST-1M project, a 4 m-diameter Davies Cotton telescope with 9 degrees FoV and a 1296 pixels SiPM camera, is designed to meet the requirements of the next generation of ground based gamma-ray observatory CTA in the energy range above 3 TeV.
In this work, a special emphasis will be given to the commissioning results of the SST-1M telescope. The latest performance validation tests such as charge resolution, trigger efficiency together with Monte-Carlo comparison will be given. Preliminary results on the observation of gamma ray emitters will be presented.
Since 2012 the IceCube detection of a diffuse population flux of astrophysical neutrinos confirmed the existence of population of sources emitting neutrinos above the 100 TeV energy scale, the nature of which remains still unknown. The sources of this diffuse neutrino high-energy excess need investigations with point-like source searches (time integrated and time dependent) and a strong multi-messenger program in synergy with other gamma-ray and other energy-band photon experiments, gravitational waves and cosmic-ray experiments. Recent results on high-energy emission from the blazar TXS 056+056 and latest results of point-source searches with 10 years of IceCube data, including observed neutrino emission excess from the active galaxy NGC 1068, will be presented.
Weak measurements [1], introduced more than 30 years ago, underwent a metamorphosis from a theoretical curiosity to a powerful resource for exploring foundations of quantum mechanics, as well as a practical laboratory tool. However, unlike in the original textbook experiment, where an experiment with massive particles is proposed, experimental applications are realized applying photonic systems. We have overcome this gap by developing a new method to weakly measure a massive particle’s spin component. Our neutron optical approach is realized by utilizing neutron interferometry, where the neutron’s spin is coupled weakly to its spatial degree of freedom [1]. This scheme was then applied to study a new counter-intuitive phenomenon, the so-called quantum Cheshire Cat: If a quantum system is subject to a certain pre- and post-selection, it can behave as if a particle and its property are spatially separated, which is demonstrated in an experimental test [2,3]. State tomography, the usual approach to reconstruct a quantum state, involves a lot of computational post-processing. So in 2011 a novel more direct method was established using weak measurements. Because of this weakness the information gain is very low for each experimental run, so the measurements have to be repeated many times. Our procedure is based on the method established in 2011, without the need of computational post processing, but at the same time uses strong measurements, which makes it possible to determine the quantum state with higher precision and accuracy. We performed a neutron interferometric [4] experiment, but our results are not limited to neutrons, but are in fact completely general. In our latest experiment [5] we investigated the paths taken by neutrons in a three-beam interferometer by means of which-way measurements, realized by a partial energy shift of the neutrons so that faint traces are left along the beam path. Final results give experimental evidence that the (partial) wave functions of the neutrons in each beam path are superimposed and present in multiple locations in the interferometer.
[1] S. Sponar, T. Denkmayr, H. Geppert, H. Lemmel, A. Matzkin, J. Tollaksen, and Y. Hasegawa, Phys. Rev. A 92, 062121 (2015).
[2] T. Denkmayr, H. Geppert, S. Sponar, H. Lemmel, A. Matzkin, J. Tollaksen, and Y. Hasegawa, Nat. Commun. 5, 4492 (2014).
[3] S. Sponar, T. Denkmayr, H. Geppert, and Y. Hasegawa, Atoms 4, 11 (2016).
[4] T. Denkmayr, H. Geppert, H. Lemmel, M. Waegell, J. Dressel, Y. Hasegawa, and S. Sponar, Phys. Rev. Lett. 118, 010402 (2017).
[5] H. Geppert ,T. Denkmayr, S. Sponar, H. Lemmel, T. Jenke, and Y. Hasegawa, Phys. Rev. A 97, 052111 (2018).
Standard diffraction experiments are routinely used to investigate the (PERIODIC) structure of materials. However, they only yield information on the amplitudes while the phase information is lost ('phase problem' of diffraction).
In this talk we will experimentally demonstrate by the example of a simple one-dimensional holographic grating how the entire information - amplitude and phase - of the Fourier components for this periodic structure can be retrieved. The wavelength of scattered radiation is intentionally chosen much smaller than the grating spacing so that diffraction occurs in the nonstandard multi-wave regime. By employing the so-called rigorous coupled wave analysis to model the angular dependence of the diffraction efficiencies we are able to determine the refractive-index profile (= the structure) of the holographic grating completely.
The search for a neutron electric dipole moment (EDM) is of significant interest in understanding the observed baryon asymmetry in the universe. Historically, two methods have been employed to measure an EDM, storage of ultracold neutrons (UCN) and cold neutron beams, with the latter being abandoned in the 1980s due to a limiting relativistic systematic effect. The BeamEDM experiment developed at the Universität Bern represents a novel concept to overcome this limitation with cold neutron beams using time-of-flight measurement. The ultimate goal of this project aims to reach a sensitivity competitive with future UCN experiments. This talk presents an overview of the experiment and the latest results.
Recent detector developments lead to enhancement of spatial resolution capabilities of neutron imaging to single digit micrometer level. At PSI, a device that enabled imaging with better than 5 micrometers spatial resolution was developed in the framework of a Neutron Microscope project and is now available to a broad neutron imaging user community at various beamlines. The progress achieved within the framework of this project will be concisely presented.
The above mentioned progress enabled new science to be pursued. Several applications of the high resolution neutron imaging will be presented, namely defects in additively manufactured gold alloys and in uranium oxide TRISO particles,hydrogen distribution in Zircaloy tubes for nuclear fuel element, and others.
Neutron beams enable a large variety of studies in fundamental physics research. In particular, neutron beta decay allows for a detailed study of the weak interaction within the standard model of particle physics and possible extensions beyond it. Among other observables, a number of correlation coefficients may be determined, providing a complementary way to high-energy accelerator experiments.
PERC, a new facility for the high-precison experimental study of neutron decay is currently constructed. It consists of a specifically tailored superconducting magnet system to guide the charged neutron decay products and a special neutron guide arrangement to conserve the initial neutron phase space density. The concept and design of the facility, various components, and information of the current status will be presented.
Neutron grating interferometry (nGI) is an established neutron imaging method that has found successful application in a wide range of scientific fields such as soft matter, magnetism and superconductors.
Here we present the latest developments that enable to achieve directional sensitivity of the scattering signal and retrieve quantitative information about the phase shift induced by the magnetic potential.
Individual charged atoms stored in ion-traps are one of the most promising architectures to build a scalable quantum computer. This presentation will provide an overview of current developments to realize high-fidelity control of an arbitrary subset of qubits in a quantum register, recent cross-verification of quantum computers across several architectures (including photons and superconducting qubits), adaptations to realize ion-trap technologies according to industry-standards, and an outlook on how to connect distant ion-trap quantum computers using a telecom-compatible photonic interface.
Daedalean set out to create a robotic pilot that can outperform the Human on every task as tested in the Commercial Helicopter Pilot skill test, on the principle that if you want to replace the human weaknesses by an automatic system, you have to outperform her on her strenghts first. This requires bringing modern robotics, computer vision and deep learning to the very conservative world of safety critical avionics.
The author is a physicist with no formal training in the use or programming of computers who bluffed his way through a career in software engineering at Google and SpaceX before.
In the last decade multiple corporations have invested heavily in quantum technologies and in particular quantum computing. As such, the number of industry jobs for physicists working in this field has increased significantly. In this talk I will highlight some of the quantum-related thrusts at Microsoft Corporation. This includes building a scalable quantum computer, the development of a complete quantum stack, as well as a focus on quantum-inspired methods with the goal of delivering immediate quantum impact today.
In parallel, I will share my personal experiences on how to jump-start a career in industry.
Over the past few decades, the amount of scientific articles and technical literature has increased exponentially in size. Consequently, there is a great need for systems that can ingest these documents at scale and make the contained knowledge discoverable. Unfortunately, both the format of these documents (e.g. the PDF format or bitmap images) as well as the presentation of the data (e.g. complex tables and figures) make the extraction of qualitative and quantitive data extremely challenging. In this talk, we will present our three pronged approach to this problem and show practical examples in the field of Material Science and Oil&Gas. We will start by introducing a scalable service [1] that is able to ingest documents at scale and exploits state-of-the art AI models to obtain very high accuracies. Next. we will show how the data contained in the ingested documents can be extracted using NLP methods. Finally, we will show how the extracted data can be efficiently queried using Knowledge Graphs and how one can obtain new insights from these graphs by applying advance analytics [2].
[1] https://www.researchgate.net/publication/325359423_Corpus_Conversion_Service_A_Machine_Learning_Platform_to_Ingest_Documents_at_Scale
[2] https://www.researchgate.net/publication/303551320_Stochastic_Matrix-Function_Estimators_Scalable_Big-Data_Kernels_with_High_Performance
Quantum computation promises exciting applications in the field of cryptography, self-learning methods and quantum simulations. Noisy small-scale quantum computers can already be used via cloud services provided by companies like IBM or Rigetti computing; and the technology is improving rapidly. HQS Quantum Simulations is a Karlsruhe-based start-up developing software for chemistry/material simulations that uses quantum computers. We aim to enable relevant utilization of (noisy) quantum computers as early as possible within the next few years, by combining high-end classical simulation methods with optimized quantum algorithms. In the presentation I briefly introduce HQS Quantum Simulations and the daily work there. I show how quantum computing can be applied to chemistry/material simulations, and discuss the possibilities and current state of quantum computing.
This talk shows two examples of applied Industrial Artificial Intelligence at Siemens Austria, which are already close to production quality and usage. They cover a broad range of AI techniques including both symbolic and data-driven AI concepts.
Firstly, a cyber-physical production system with co-operating robots, optimal production planning and deductive reasoning for a so-called producibility check where the product steers its production. Secondly, an application with autonomously flying vehicles (drones) with high-resolution cameras and an image analytics algorithm with machine learning for anomaly detection to spot failures on power line systems.
For such state-of-the-art multi-disciplinary applications new job profiles emerge. Talents understanding physics and informatics plus some background in data analytics and statistics are necessary to cope with those challenges.
Using an atomic defect in diamond, an NV center, we can image miniscule magnetic fields and currents at the nm scale in the lab. Bringing this quanutm technology to a broader market in a turn-key system is the challenge now facing our start up, QZabre LLC. I will talk about our efforts and experiences in moving from research to product development.
Chiral magnetic skyrmions arise due to the Dzyaloshinskii-Moriya interaction (DMI) as a result of the spin-orbit interaction in magnets lacking bulk or structure inversion asymmetry. I start my talk with a micromagnetic formulation of the energy functional and discuss briefly some general fundamental aspects. Using then a three-pronged scale-bridging approach combining DFT calculations with a generalized spin-lattice model containing the Heisenberg, DMI as well as magnetic anisotropy and dipolar interaction, with micromagnetism, we explore materials combinations for interfaces that offer great potentials hosting skyrmions, investigate their phase diagram, stability, lifetime and dynamics, their size as function external magnetic and temperature. We study optimal parameters for the detection by transport. I present our efforts to find skyrmions compatible to technology requirements.
Antiferromagnetic skyrmion crystals are spatially periodic noncollinear magnetic phases predicted to exist in antiferromagnets with Dzyaloshinskii-Moriya interactions. We show for the first time that their bulk magnon band structure, characterized by nonzero Chern numbers, is topologically nontrivial and that they support topologically-protected chiral magnonic edge states. Of particular importance for experimental realizations, magnonic edge states appear within the first bulk magnon gap, at the lowest possible energies they can exist and where magnon-magnon interactions are reduced. Thus, antiferromagnetic skyrmion crystals show great promise as novel platforms for topological magnonics.
[1] S. A. Díaz, J. Klinovaja, and D. Loss, arXiv:1812.11125; Phys. Rev. Lett. (accepted).
The nanometer-scale vortex-like spin textures, such as vortex-anrivortex pairs in ferromagnetic (FM) domain walls [1], votices in superconductors [2], skyrmion (lattice) [3] and antiskyrmions [4] in magnets with inversion symmetry, have recently attracted enormous attention owing to their topological manner[5]. To confirm such minute complex spin textures and their dynamics with external stimuli, the real space observation have been performed by Lorentz transmission electron microscopy (TEM).
[1] X.Z. Yu, et al., Adv. Mater. 29, 1603958 (2017).[2] A. Tonomura, et al., Nature 397, 308 (1999). [3] X.Z. Yu, et al., Nature 465, 901 (2010).[4] Ajaya K. Nayak, et al., Nature 548, 561 (2017).[5] N. Nagaosa and Y. Tokura, Nat. Nanotechnol. 8, 899 (2013).[6] X.Z. Yu, et al., Nature 564, 95 (2018).
In a β-Mn-type chiral magnet Co9Zn9Mn2, we demonstrate the magnetic field-driven collapse of a room temperature metastable skyrmion lattice (SkL) to pass through a regime of partial topological charge inversion. Using Lorentz transmission electron microscopy, we observe the magnetization distribution directly as magnetic fields are applied antiparallel to the original skyrmion core magnetization. Topological protection prevents the transition of the SkL to the helical state, instead, for increasingly negative fields, the metastable SkL transforms into giant topological bubbles. These structures give way to form a near-homogeneously magnetized medium that hosts isolated skyrmions with inverted cores. From micromagnetic simulations, we find that the observed regime of partial topological charge inversion has its origin in the topological protection of the starting SkL.
Skyrmions are topologically protected spin textures that appear in certain chiral magnetic materials. One bulk chiral material in which skyrmions are observed is the multiferroic insulator Cu2OSeO3. In this talk I will present small angle neutron scattering (SANS) and magnetometry work studying skyrmion metastability in zinc-substituted Cu2OSeO3. This substitution dramatically increases the metastable lifetime of skyrmions, by a factor 50 with just 2.5% Zn. Furthermore, we can use SANS to measure the formation time of skyrmions out of the conical state when an electric field is applied to Zn substituted Cu2OSeO3. The temperature dependence of these formation times follow an Arrhenius law dependence, allowing us to extract an energy barrier for the formation of skyrmions of 1.57 eV.
The chiral ferrimagnet Cu2OSeO3 hosts topologically protected spin textures known as magnetic skyrmion lattices and exhibit characteristic magnon band structures. We conducted scanning Brillouin light scattering (BLS) spectroscopy on bulk-shape single crystals of Cu2OSeO3 at low temperature with magnetic field applied along (100). Multiple magnon modes were observed in conical and field-polarized state and attributed to bulk magnon modes with a high wavevector of up to k = 35.6 rad/micrometer. BLS studies hence enable one to explore anisotropic characteristics of magnon bandstructures for differently oriented Cu2OSeO3 crystals. This work is support by SNSF via 171003 and DFG TRR80.
Neutron scattering was used to study frustrated MnSc2S4 spinel with magnetic Mn2+ ions forming the diamond lattice [1]. We present direct experimental evidence for the existence of the spiral spin liquid, which was predicted to occur within the J1-J2 model, when the ratio between the first and second neighbour couplings is |J2/J1|>0.125, unravel three long-range ordered phases supplanting each other on temperature lowering and disclose the triple-q state in applied magnetic fields.
With Monte Carlo simulations we scrutinize further details of the spin Hamiltonian, ie. the 3rd neighbour coupling, single ion anisotropy and exchange anisotropy and establish that this set of parameters stabilizes the lattice of dense topological objects akin to skyrmions.
[1] S.Gao, O.Zaharko, V.Tsurkan, et al. Nature Physics,13,157–161(2016).
The field of terahertz (0.1-10 THz) science and technology has had an exotic standing for a long time, due to the lack of performant sources and detectors. In this range, both electronics and optics fail to provide a performant solution. The scope of this work was to initiate experiments in quantum optics at terahertz frequencies, which lead to the exploration of the characteristics of quantum states of light in the time-domain. Using in-house developed ultrasensitive field measurement techniques we measure, for the first time, the field correlation on the electromagnetic vacuum state as a function of time and space.
Positronium and Muonium are excellent systems to test bound-state QED theory to high precision. This has motivated numerous precise experiments aimed at measuring the hyperfine splitting and 1S-2S transition of these atoms.
Currently, there is some disagreement with the most recent bound-state QED calculations for the hyperfine splitting in positronium. Our approach to resolve this, PHySES, eliminates several possible sources of systematics present in earlier experiments by a novel experimental design.
Furthermore, measurements of the 1S-2S transition can test bound state QED in the ppb range and determine fundamental constants, e.g., the muon mass.
Here we present current efforts to reach this sensitivity.
Spatial hole burning prevents single-frequency operation of thin-disk lasers when the thin disk is used as a folding mirror. We present an evaluation of the saturation effects in the disk for disks acting as end-mirrors and as folding-mirrors explaining one of the main obstacles towards single-frequency operation. It is shown that a twisted-mode scheme based on a multi-order quarter-wave plate combined with a polarizer provides an almost complete suppression of spatial hole burning and creates an additional wavelength selectivity that enforces efficient single-frequency operation. We want to discuss the disadvantages and benefits of spatial hole burning in different laser systems.
The ground state of electromagnetic radiation is characterized by the presence of fluctuating zero-point electric fields. A direct method to characterize their spectral composition is still missing. In this work, we present the first direct electric field correlation measurement on the electromagnetic vacuum state at terahertz frequencies. It presents a peak value of 6.20 *10^-2 volts squared per square meter at zero time delay. Its measurement has been performed using a combination of electro-optic detection and ultrashort pulses. The spatial dependence of the field coherence has been investigated, together with the influence of the probed space-time volume on the detection bandwidth. We also provide a model for the quantitative prediction of the experimental result.
We study a paradigmatic quantum-optical model, where a collection of two-level systems interact with both quadratures of a cavity mode. The closed system exhibits rich physics, including discrete and continuous symmetry-breaking phase transitions. Exploring the dynamical response, we find an additional transition manifesting in the system's frequency response. Particle-hole like processes exchange due to a soft mode gap closing. In the driven-dissipative version of this model the phase diagram is profoundly altered. Novel regions of coexistence of phases appear at the expense of broken continuous symmetry transitions. Using Keldysh formalism, we show that the phase transition in frequency domain survives and the system shows signature of a Fano resonance. Our predictions pave the way for experimental observation of this effect.
Low-temperature decoherence in many quantum systems, such as magnons or NV centers, is attributed to the interaction with the atomic impurities in the sample. We propose a model describing effective dynamics of a harmonic oscillator in the presence of impurities based on master equation formalism, to model such behaviour. Impurities are modelled as a bath of two-level atoms, which is a rather unconventional scenario, since in the context of quantum optics the bath is usually bosonic. We use our model to study the dependence of the Kittel magnonic mode linewidth in a Yittrium-iron-garnet sphere in a ferromagnetic resonance experiment, where the driving field affects not only the magnon, but also the two-level atoms, and compare our results with recent experiments.
Elastic strain engineering utilizes stress to realize unusual material properties. Here we show that geometric strain engineering combined with soft-clamping can produce unprecedentedly high quality factor nano-mechanical resonators. Specifically, using a spatially non-uniform phononic crystal pattern, we co-localize the strain and flexural motion of a SiN nano-beam, while increasing the former to near the yield strength. This combined approach produces string-like resonators with room-temperature Q × f > 1015 Hz, far exceeding previous values for a mechanical oscillator of any kind. At room temperature, this device can achieve force sensitivity of ~1 aN / sqrt(Hz), performs hundreds of quantum coherent cycles, and attain Q > 109 at megahertz frequencies.
When particles with opposite spin scatter, momentum is transferred from one spin species to the other causing a spin drag - a friction between the relative motion of the two spin components. This phenomenon is relevant for spintronics devices, and has also been explored in experiments with ultracold atoms. Motivated by recent experiments [1,2], we consider spin drag in a one-dimensional quantum wire. For attractive interactions, a nonzero spin drag is caused by pairing of fermions with opposite spin. We investigate analytically and numerically the possibility of spin drag when interactions are repulsive and the ground state is a spin density wave.
[1] S. Krinner et al., PNAS 113, 8144 (2016)
[2] M. Lebrat et al., PRX 8, 011053 (2018)
By solving the Bogoliubov--de Gennes equations analytically, we derive the fermionic zero-modes satisfying the Majorana property that exist in vortices of a two-dimensional $s$-wave Fermi superfluid with spin-orbit coupling and Zeeman spin-splitting. The Majorana zero-mode becomes normalisable and exponentially localised to the vicinity of the vortex core when the superfluid is topologically non-trivial. We calculate the energy splitting due to Majorana hybridisation and identify that the $s$-wave Majorana vortices obey non-Abelian statistics.
The Pauli exclusion principle $0 \leq n_k\leq 1$ is a kinematical constraint on fermionic occupation numbers which strongly shapes fermionic quantum systems on all length scales. We demonstrate that this fundamental restriction can also be interpreted dynamically: the fermionic exchange symmetry manifests itself in the one-fermion picture in the form of an ``exchange force'' which repulsively diverges on the boundary of the allowed region, preventing fermionic occupation numbers $n_k$ from leaving their domain $0 \leq n_k\leq 1$. Moreover, for translationally invariant one-band lattice models, we exploit the knowledge of the natural orbitals (momentum states) and discover the form of the exact one-particle reduced density matrix functional $\mathcal{F}(\vec{n})$. Remarkably, $\mathcal{F}(\vec{n})$ turns out to be strongly shaped by Pauli's exclusion principle.
We show electronic transport data on a particular interesting carbon system: Two vertically stacked layers of graphene that are twisted with respect to each other. With the twist angle, the properties change fundamentally. The two layers are decoupled at large and strongly coupled at small angles. It is even possible to achieve superconductivity at a certain twist angle.
To probe the system we make use of an electronic Fabry-Pérot interferometer. We probe a network of topological channels at tiny twist angles [1] and the physics of decoupled graphene layers at very large twists.
[1] P. Rickhaus, et.al. Nano Lett. 18, 11, 6725 (2018)
We investigate the electronic structure of IrTe$_2$ to elucidate the origin of its charge-ordered phase transitions. Here, we present an X-ray photoemission spectroscopy study as a function of temperature across the IrTe$_2$ phase transitions. Our surface sensitive measurements reveal new results on the specific nature of the transitions in contradiction with the literature. According to our measurements, the transition at 270 K remains first-order, occurring within only a few Kelvin, while the transition at 180 K is second-order, developing over a range of several tens of Kelvin. In parallel, we perform an angle-resolved photoemission spectroscopy study as a function of temperature, which allows us to confirm the previous deductions.
Novel properties and exciting perspectives are offered by two-dimensional magnetic materials, like binary MX2 and ternary MYZ3 (M is a metal element; X is a halogen; Y = Si, Ge or P; Z is a chalcogen). Various complementary growth techniques are employed to produce these materials in crystalline form, namely the Chemical Vapor Transport and the high temperature solution (flux) growth. Here we summarize the growth techniques and conditions, as well as the recent advances in the crystal growth of magnetic van der Waals materials. The quality of the bulk crystals is proven by structural and chemical investigations and the study of magnetic properties. These materials can be successfully exfoliated and are being applied in atomically thin devices.
The electronic structure of 2D materials undergoes significant changes as their thickness is reduced down to the atomic limit. In few layer black phosphorus (BP) crystals, a promising semiconductor for optoelectronic and electronic applications, the bandgap increases drastically and the effective mass at the valence band and conduction band edges changes significantly. Here, we present the first direct electronic structure measurements on ultrathin BP. As BP is an air sensitive material, this is achieved by encapsulating exfoliated flakes in graphene or hBN. Our results reveal the quantum well states in the valence band and give a mapping of the anisotropic bandstructure of thin BP flakes. In particular, we determine the anisotropic effective mass at the valence band edge.
We will report on a templated electrochemical technique for patterning arrays of single-crystalline Si nanowires with feature dimensions down to 5 nm. This technique, termed three-dimensional electrochemical axial lithography (3DEAL),[1] allows the design and parallel fabrication of hybrid silicon nanowire arrays decorated with complex metal nano-ring architectures in a flexible and modular approach. 3DEAL is based on simple chemical and electrochemical approaches that were developed previously[2] and can produce homogeneous macroscale metal-Si wire arrays.
[1] F. J., Wendisch, M. Saller, A. Eadie, A. Reyer, M. Musso, M. Rey, N. Vogel, O. Diwald, G. R. Bourret Nano Letters 2018, 18, 11, 7343-7349
[2] T. Ozel, G. R. Bourret and C. A. Mirkin Nat. Nanotech. 2015, 10, 319–324
We have previously demonstrated a novel approach for the growth of III-V nanowires on Si, using focused ion beam (FIB) -implanted Ga as nucleation points for self-catalysed GaAs nanowire growth. In this work, we have further investigated the possibility of growing optically active nanowires using this technique, via the growth of GaAs nanowires containing single InGaAs quantum wells in the shell. The nanowires show good emission, proving the high material quality of NWs grown via FIB-implantation. By comparison with randomly nucleated NWs, we find some C-doping of the NW core, attributed to the implantation process.
Graphene is a promising candidate for nano-electronic devices, due to the expected long spin lifetimes and high carrier mobilities. Improvements in fabrication for graphene nanostructures have leveraged their quality to such an extent, that quantum dots in bilayer graphene are comparable to the best devices in gallium arsenide [1].
We use finite bias spectroscopy to identify the single-particle and many-body ground- and excited states of electrostatically-defined quantum dots in bilayer. The results of our experiments allow us to propose a clear level scheme for two-particle spectra, in which the spin- and valley-entanglement and the exchange interactions play a crucial role [2].
[1] M. Eich, et al., Phys. Rev. X 8, 031023 (2018).
[4] A. Kurzmann, et al., arXiv:1904.07185 [cond-mat.mes-hall] (2019).
Bilayer-Graphene based Nanostructures promise unique opportunities in the field of quantum electronics. However, the endeavor to form quantum electronic building blocks such as Quantum Point Contacts (QPCs) and Quantum Dots (QDs) is significantly hampered by the presence of disorder.
To understand the influence of disorder on the formation of QPCs and QDs in Graphene, we employ Scanning Gate Microscopy on a 3um-long, splitgate-defined channel on encapsulated bilayer graphene. By scanning the voltage-biased metallic tip of an atomic force microscope over the graphene channel, we perturb the potential landscape of the channel locally. This allows us to infer the local disorder potential within the channel.
This talk focus on the control and understanding of a gravitationally interacting elementary quantum system using the techniques of gravitational resonance spectroscopy (GRS) and ultracold neutrons (UCN). It offers a new way of looking at gravitation at short distances based on quantum interference.
In the past years, the qBOUNCE collaboration designed and built a new Ramsey-type experiment at the Institute Laue-Langevin (Grenoble). In 2018, we were able to measure gravitational state transition with the complete assembled experiment for the first time. In June 2019, another 200 days of measurements will start.
We will present the status of the data analysis and a novel search strategy using GRS to differentiate between Einstein’s cosmology constant and dark energy theories.
MAGIC and FACT investigate the very-high-energy (E>100GeV) gamma rays emitted by blazars, whose relativistic jets points towards the observer. Past observations have revealed that the blazar 1ES2344+51.4 can show strong flux variability and the spectral energy distribution shifts towards unusual high energies during flares. We report a flaring episode of 1ES2344+51.4 during August 2016, where the VHE flux measured by MAGIC and FACT is comparable to the historical maximum, while the spectrum is the hardest for this object above 100GeV. Combining multi-wavelength observations, we obtain an unprecedented characterisation of the inverse Compton peak.
A precise characterization of neutrino oscillation parameters is very important to search for physics beyond the standard model. T2K, located in Japan, is one of the leading long-baseline neutrino oscillation experiments. It measures a muon (anti-)neutrino flux, with energy peaked at ~0.6 GeV, produced at the J-PARC facility 295 kilometers east of the SuperK far detector. One of the most important limiting factors to precise oscillation measurements are the systematic uncertainties on the neutrino-nucleus interactions. A near detector, ND280, located at 280 meters, is used to constrain the flux of the beam and gain better understanding of the nuclear effects which are poorly understood. We will present the latest techniques and results from cross-section measurements at the near detector.
Supersymmetry and Grand Unified Theories predict several nucleon decay modes with lifetimes between $10^{28}$ and $10^{39}$ years. The Deep Underground Neutrino Experiment (DUNE) will be able to test many of the predicted decay modes for lifetimes up to $10^{35}$ years. DUNE's far detector will comprise four 10-kiloton Liquid Argon Time Projection Chambers (LAr TPCs) installed 1475 meters underground. Its design combines high precision calorimetry with an exposure of several 100 kiloton-years in a low-background environment, which makes it especially suitable for proton decay searches via $p \rightarrow K^+ + \bar{\nu}$. I will present a sensitivity study for this channel in DUNE, using a fully simulated and reconstructed signal and atmospheric neutrino background sample in a 10-kiloton dual phase LAr TPC.
The discovery of neutrinoless double beta decay would establish neutrinos as Majorana fermions and imply a violation of lepton number conservation. The leading experiment based on $^{76}$Ge is GERDA, which operates a 36\,kg array of germanium detectors, enriched in $^{76}$Ge directly immersed in liquid argon. The argon acts a a coolant and active shield against background radiation due to its scintillating capabilities. GERDA was the first experiment in the field to reach a half-life sensitivity of $10^{26}$\,yr, and it will take data until the end of 2019. Its successor is LEGEND-200, which will operate about 200\,kg of enriched $^{76}$Ge-detectors in liquid argon at LNGS. We will present the latest results of GERDA and plans for LEGEND-200 and beyond.
The DARWIN experiment is a next-generation dual-phase time projection chamber which will operate 50 tonnes of natural xenon and whose primary goal will be to explore the entire experimentally accessible parameter space for WIMPs. Besides its unprecedented sensitivity to WIMPs, such a large detector, with its low-energy threshold and ultra low background level, will also be sensitive to other rare interactions like the neutrinoless double beta decay of 136Xe. In addition, DARWIN will be able to measure low energy solar neutrinos, observe the coherent neutrino-nucleus interaction and detect galactic supernovae. We discuss here the concept of DARWIN and the sensitivity for the different physics channels.
DARk matter WImp search with liquid xenoN (DARWIN) will be a direct dark matter detection experiment using a multi-ton time projection chamber at its core. While DARWIN is designed to explore the entire experimentally accessible parameter space for WIMPs, the detector will also be sensitive to other rare interactions. One ambitious goal is the search for the neutrinoless double beta decay of 136-Xe which has an abundance of 8.9% on natural xenon. We present the sensitivity estimation of DARWIN to this rare nuclear decay process, based on detailed Monte Carlo simulations of the backgrounds from detector materials, intrinsic sources to the xenon, as well as solar neutrinos.
MicroBooNE is the first of three liquid argon time projection chambers (LArTPCs) of the Short-Baseline Neutrino Program at Fermilab. Located on the Booster Neutrino Beamline, MicroBooNE has been collecting data since October 2015 to determine the source of the low-energy electromagnetic event excess previously reported by MiniBooNE and LSND. In addition, MicroBooNE is studying neutrino interactions on liquid argon, measuring low-energy neutrino cross sections, and developing technological advancements for future LArTPC experiments such as DUNE. This talk will give an overview of the MicroBooNE experiment, as well as discussing the principal physics goals of MicroBooNE and highlighting recent physics results.
Angle-resolved photoemission spectroscopy (ARPES), and its extension in the time-resolved regime (TR-ARPES), has revealed to be a powerful technique to study of unconventional superconductivity. In this contribution I will present our TR-ARPES measurements on the cuprate Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. By employing a pulse of duration comparable to the timescales of the superconducting state we demonstrate the capability of the pump pulse to manipulate the phase fluctuations [1] and the electron-bosons coupling [2] independently of the pairing.
[1]F. Boschini, E. H. da Silva Neto, E. Razzoli, et al., “Collapse of superconductivity in cuprates via ultrafast quenching of phase coherence” Nature Materials 17, 416(2018).
[2]E. Razzoli, F. Boschini et al., “Ultrafast reduction of electron-boson kink induced by phase coherence loss in cuprates” in submission(2019).
Revealing the dynamics of collective excitations (e.g. excitons, phonons, plasmons, magnons…) in quantum materials is a central topic in condensed matter physics, as collectivity lies at the origin of several cooperative phenomena that lead to profound transformations, instabilities and phase transitions. Here, we will explore the dynamics of such collective excitations from the perspective of ultrafast science, presenting novel spectroscopic methods that can track the real-time evolution and the interactions of distinct collective modes. Special emphasis will be given to the rising fields of excitonics and phononics in materials governed by strong interactions and correlations.
Furka, the end-station for condensed matter and quantum materials at Athos beamline, will be dedicated to time resolved Resonant Inelastic and Elastic X-ray Scattering (tr-RIXS and tr- REXS) and time-resolved soft X-ray diffraction (tr-SXRD) studies. The intriguing properties of correlated materials originate from the strong coupling between charge, orbital, spin, and lattice degrees of freedom. Ultrafast spectroscopy and tr-SXRD are unique tools to disentangle different degrees of freedom. After a brief overview of the Athos project describing its unique features, we will present the Furka’s scientific case giving a general concept of the instrument. In the future it will be investigated the option to perform experiments in the nonlinear optics regime, taking advantage of the multicolour and TeraWatt-attosecond pulses provided.
Magnonics, the study and development of devices utilising collective spin excitations, is a rapidly growing field, covering both fundamental topics (antiferromagnetism, quasiparticle condensates) and technological applications (MRAM, spintronics). Yttrium iron garnet (YIG) is a ferrimagnetic insulator with the lowest known magnon damping factor of any material. This low damping leads to a prevalence of nonlinear effects and notably the room temperature Bose-Einstein condensation (BEC) of magnons first reported by Demokritov et al in 2006, and subject of a number of investigations since. Ultrathin structures will be required for applications but remain largely unexplored. Here I report on the design, fabrication and characterization of microwave devices based on such ultrathin structures (YIG thickness~100 nm). The spin wave dynamics were measured using both Brillouin Light Scattering (BLS) and time resolved scanning transmission x-ray microscopy (TR-STXM), locked in phase with microwave stimulation of the devices. A number of milestones are reached for our novel devices. First, we have explicitly measured the spin wave dispersion in YIG, and demonstrated the existence of the finite momentum minimum required for magnon BEC. Second, the BLS data demonstrate that the condensate exists in our samples. These results are a key development towards adding condensate phenomena to the thin film magnonics toolbox.
Ultrafast electron microscopy provides the possibility to conduct time-resolved experiment in three independent dimensions: real space, reciprocal space and energy domain. Being promising for condensed matter and material research it also serves as a platform for electron-light interaction. There are two mechanisms which facilitate the strong interaction regime: interaction with near-fields and interaction via inverse transition radiation. We utilise these effects to demonstrate:
1) Momentum exchange between electron and photon;
2) Generation of electron vortex facilitated by orbital angular momentum conservation upon absorption of circularly polarized photons
3) Coherence interaction involving multiple optical fields, used for time-holography of optical fields.
Zurich Instruments AG was founded in 2008 as a spinoff of ETH Zurich's Physics Department. Since then the company has grown to more than 70 people in 6 countries and serves advanced research laboratories with best-in-class measurement instruments. After successfully disrupting the lock-in amplifier market, Zurich Instruments started to engage in quantum computing about 3 years ago. Today Zurich Instruments aims at establishing the first commercial quantum computer control system in the world. The presentation tells the story of how things happened, the challenges the company is facing today and how you fit in.
Being a theoretical physicist by training, I will retrace my path from quantum information theory as a postdoc in academia to machine learning research in the corporate world at the Bosch Center for Artificial Intelligence. I will describe research challenges that await physicists in the corporate research division at Bosch, in the fields of both quantum technologies and machine learning.
Quantum effects not only provide deeper insights into fundamental physics, but can also be exploited to advance a broad range of technologies. TOPTICA Photonics is deeply rooted in the quantum technology community, developing and manufacturing high-end laser systems for scientific and industrial applications. I will present opportunities and challenges TOPTICA faces by providing enabling technologies for quantum technologies and give examples of TOPTICA’s direct involvement in this field, e.g. the development of an optical atomic clock. My own career path reflects the entanglement between academic research and industry, as my curiosity for quantum effects and enthusiasm for technology took me from research on quantum effects at ETH Zurich and MPQ Garching to become TOPTICA’s Application Specialist for Quantum Technologies.
The commercial potential of artificial intelligence and the promise of quantum computing has increasingly opened the door for researchers to step outside the academic world to apply their skills at global tech companies and startups.
I will give a brief overview of typical entry points, roles and topics and open up the forum for a Q&A session.
The transfer is done by public transportation. Tram departure at the stop "Irchel". For detailed information see the black board at the registration desk.
Only for participants who have registered in advance. On-site registration is not possible.
Nanowires are filamentary crystals with a tailored diameter in the range of few tens of nanometers. Their particular morphology and size renders them particularly attractive for a manifold of applications and fundamental experiments. We present recent results in the area of compound semiconductor nanowires. We review the fundamental properties that render them attractive for solar cells and quantum technologies. We will show their enhanced light absorption results in materials savings up to a factor 1000 thanks to photonic properties and enahnced carrier collection.Finally, we propose a novel setting for the growth of nanowire networks in a scalable manner. So far, these structures have been considered for topological schemes of quantum computing (using Majorana Fermions that are topologically protected).
Artificial photosynthesis is a direct and promising option to store solar light as sustainable hydrogen fuel. However, the water oxidation half reaction remains a serious bottleneck for applications and a major challenge for catalyst design. To this end, we pursue a three-pillar approach. (1) Bio-inspired strategies: Our recent progress includes tailored cobalt cubane cut-outs of oxide catalyst surfaces or unraveling new soft-templating strategies in a high-performance electrocatalyst.[1] (2) Targeted nanomaterials design: We established facile pathways to environmentally friendly InP/ZnS quantum dots for hydrogen production or to transition metal electrocatalyst-carbon nanotube architectures.[2, 3] (3) Monitoring the synthetic and operational pathways of water oxidation catalysts: We obtained new insight into the operando properties of unconventional non-oxide electrocatalysts and into unexpected formation pathways of cobalt oxide nanocatalysts.[4] Furthermore, we pursue overarching concepts to bridge molecules and solids in artificial photosynthesis, e.g. through hybrid photoanodes and single atom catalysts on graphene supports. These strategies will finally be contrasted with our work on oxide materials for solar-driven thermochemical CO2 splitting.[5]
[1] F. Song, K. Al-Ameed, M. Schilling, T. Fox, S. Luber, G. R. Patzke, J. Am. Chem. Soc. 2019, DOI: 10.1021/jacs.9b01356.
[2] S. Yu, X.-B. Fan, X. Wang, J. Li, Q. Zhang, A. Xia, S. Wei, L.-Z. Wu, Y. Zhou, G. R. Patzke, Nat. Comm. 2018, 9, 4009.
[3] W. Wan, S. Wei, J. Li, C. A. Triana, Y. Zhou, G. R. Patzke, J. Mater. Chem. A 2019, in print.
[4] R. J. Müller, J. Lan, K. Lienau, R. Moré, C. A. Triana, M. Iannuzzi, G. R. Patzke, Dalton Trans. 2018, 47, 10759.
[5] R. Jacot, J. M. Naik, R. Moré, R. Michalsky, A. Steinfeld, G. R. Patzke, J. Mater. Chem. A 2018, 6, 5807.
(combined session)
We present a model for the spread, transmission, and competition of skills in a population of individuals with finite life span and asexual reproduction. Emphasis is placed on the role of spatial mobility of individuals. In the initialization, individuals may have no skill or either skill A or B. Later on, individuals are born unskilled and may acquire skills by being taught from a skilled individual. Skill A results in a small reproductive advantage but is easy to transmit, whereas skill B is harder to teach but results in a higher benefit. The model exhibits a rich behavior including phase transitions at critical migration rates.
The coupled dynamics of the radial profiles (magnetic and kinetic) in a tokamak
are described by a set of non-linear partial differential equations. RAPTOR is a
control-oriented core transport code, solving these equations based on empirical
or first-principle-based models for the heat transport. The present work presents
the extension of RAPTOR to allow rapid calculation of consistent stationary
solutions, either imposing all actuator inputs, or the plasma loop voltage. The
fast stationary state solver is embedded in a numerical optimization algorithm,
yielding a valuable tool for optimization of the flat-top phase of tokamak dis-
charges. Formulating different parameter optimization problems, this tool can
rapidly explore advanced tokamak scenarios, optimizing confinement and exter-
nal power requirements.
Non-thermal electron distributions can be generated by various means in magnetically confined plasmas. On TCV, non-thermal electron populations are routinely generated using electron cyclotron current drive (ECCD), in the presence of magnetohydrodynamic (MHD) instabilities and during disruptions. The kinetic energy of the non-thermal electrons can range from several tens to a few hundred kilo electron volts. Diagnosis of the non-thermal electrons can be partially achieved using electrn cyclotron emission (ECE) radiometers, measuring emission in the frequency range 70GHz to 140GHz. On TCV, a suite of ECE radiometers exists and there are several lines of sight available to make measurements. We will describe the available instrumentation, lines of sight, calibration and examine the potential analysis techniques open to us.
Understanding turbulence and anomalous transport in tokamaks remains an important open issue in plasma physics for fusion devices. A prominent feature of turbulence in the edge region of a plasma are coherent filamentary plasma structures that drift across the magnetic field lines at high velocities (~km/s).
In 2018, commissioned a Gas Puff Imaging (GPI) diagnostic at TCV. Data is acquired with an avalanche photo-diode array at 2MHz, such that we can resolve structures with the diameter of the order of a cm with velocities of the order of km/s. We will present size and velocity distributions of the filaments, obtained with pattern recognition algorithms, and compare them to previous, more indirect measurements deduced from electrostatic diagnostic probes.
Cellulose is a carbohydrate present at least in the composition of food, paper, textile and wood. In wood it is the most abundant component. The thermal characteristics of the polysaccharide cellulose in relation to forest fire are mainly:
specific heat, exothermic decomposition (pyrolysis) onset temperatures, enthalpy of decomposition (pyrolysis), (self)-ignition temperature, heat of combustion, explosion parameters, flammability. Data of most of these parameters will be indicated and the instruments used for their determinations (high pressure Differential Thermal Analysis (DTA), heat flux calorimetry, Siwek 20 l sphere,...) will be presented briefly (1).
Strategies of intervention against forest fire will also be proposed for discussion.
1) A. Raemy, P. Lambelet and J. Loeliger, Thermochim.Acta, 95 (1985) 441-446.
High-power laser oscillators are a simple, compact and reliable alternative to multi-stage laser amplifier systems. In particular, Kerr lens mode-locked (KLM) thin-disk laser (TDL) oscillators are capable of generating directly sub-100-femtosecond pulse durations at megahertz repetition rates and high average powers. Peak powers at the mega-watt level enable to drive non-linear processes outside as well as inside the laser cavity. We present recent advances in ultrafast KLM TDL oscillators and discuss their application for broadband THz and intracavity high harmonic generation.
Broadband and high-power THz radiation spanning several THz at mW power levels is so far available using highly complex multistage laser amplifier systems or large-scale facilities. We demonstrate a broadband THz source (spanning nearly 5 THz at 0.3 mW of average power) based on optical rectification in GaP driven directly by an ultrafast high-power thin-disk laser oscillator. The synergy of low-complexity, high average power and a broad spectrum will benefit many spectroscopic and THz imaging applications.
C$_2^-$ and other anionic molecules produced in an electric discharge in an Even-Lavie valve are accelerated to 1.8 keV in a pulsed electric field; the C$_2^-$ is then mass selected in a Wien filter. Subsequent deceleration in the static electric field of a resistive tube with a potential difference of 1.8 kV reduces the energy of the particles to a trappable range. A digital RF trap on the same 1.8 kV potential stores the C$_2^-$ molecules for subsequent experimentation with cooling lasers. A successful cooling of anionic C$_2^-$ would open up novel experiments based on sympathetic cooling of antiprotons and other anionic systems to sub-Kelvin temperatures.
The mid-infrared spectral region is referred to as fingerprint region since molecules have their unique fundamental absorption features there. Addressing this optical regime, quantum cascade technology provides innovative optoelectronic devices to significantly improve integration and performance in chemical sensing. In this work, we present a room-temperature monolithically-integrated quantum cascade laser detector device for on-chip liquid-sensing of µl-samples, with a footprint smaller than a ping-pong ball. A surface plasmon polariton waveguide connecting laser and detector enables high coupling efficiencies and maximizes the interaction volume with the surrounding analyte. Concentration-dependent absorption, rapid-response and long-term-stability measurements are shown in the first proof-of-principle experiments.
Quantum cascade laser (QCL) has established itself as the main laser source in the mid-infrared portion of the electromagnetic spectrum. Due to a substantial third-order non-linearity in the laser active region, QCLs can work in a self-starting frequency comb regime, making them interesting for spectroscopic applications. A model based on Maxwell-Bloch equations was developed in order to study phase locking dynamics of a free running mid-infrared QCL frequency comb. A thorough study of the impact of the dispersion and optical non-linearities on the cavity mode dynamics was conducted. Recent experimental findings, showing chirped frequency modulated output, were reproduced for the first time, giving important insight into the governing mechanisms responsible for the modal phase-locking.
We present a dual-comb spectrometer consisting of a free running frequency comb quantum cascade laser (QCL) and its Doppler shifted counterpart reflected from a fast scanning mirror. The stable multi-heterodyne signal is centered at $\sim$ 400 kHz and well defined by the linear scanning velocity of the reflector. This dual comb spectrometer features higher stability than the standard dual comb spectrometers, in which the mutual coherence of the two utilized combs limits the acquisition time to typically less than tens of $\mu$s. This brings indeed a great simplification compared to dual comb spectrometers, where the phase noise of the combs needs to be either actively suppressed or measured continuously and adaptively adjusted.
Quantum cascade lasers (QCL) are a compact and electrically pumped source of coherent mid-infrared light. Recently, it was discovered that QCLs can operate as frequency combs whose output is characterized by suppression of amplitude modulation and strong frequency modulation. However, the generation of short pulses by mode-locking of mid-infrared QCLs remains challenging to date due to their ultrafast gain dynamics. We report on active mode-locking of mid-infrared QCLs resulting in the emission of intense picosecond pulses. We investigate the temporal dynamics of the QCL using both linear and quadratic autocorrelation techniques. Both methods confirm independently that the QCL emits a train of isolated pulses.
Frequency combs are ideal candidates to realize miniaturized spectrometers without moving parts. We present an overview of our current research on mid-infrared frequency comb generation using interband and quantum cascade lasers (ICLs and QCLs). Our work ranges from fundamental laser physics to the realization of monolithic devices. We will highlight similarities and differences between these two types of lasers and show how both frequency modulated and pulsed frequency combs can be realized. In the last part, we will discuss why the ICL comb platform is a perfect candidate for the realization of miniaturized and battery driven mid-infrared spectrometers.
THz radiation is subject to a wide range of research and technological efforts, but it is limited by a lack of compact and powerful THz sources. A promising candidate is the quantum cascade laser (QCL), although it currently requires cryogenics since they only operate below 200 K. We present the first THz QCL operating on a thermoelectric cooler, up to a record-high temperature of 210 K. The design achieves high-temperature operation thanks to a systematic optimization by means of a nonequilibrium Green's function model, which also reliably reproduces the experimental results. Thanks to the relatively high peak power measured at 206 K (>1 mW), the laser spectra were acquired with a commercial room-temperature detector, making the whole setup cryogenic free.
We present the first interband cascade lasers fabricated into ring-shaped cavities emitting in continuous wave operation. A second order distributed feedback grating is used for single mode emission and light outcoupling in vertical direction through the GaSb substrate. In addition, the implementation of an epitaxial-side down mounting scheme facilitates improved heat transport from the active region. The devices with a waveguide width of ~5 µm and an outer diameter of 800 µm show light emission at a wavelength of ~4.38 µm. These newly developed devices are employed in a project for trace gas analysis via the principle of photothermal interferometry.
The performance of state-of-the-art GaAs-based THz-QCLs is limited by parasitic LO phonon transitions, preventing above-200 K operation. This can be overcome by using material systems with higher LO-phonon energies like ZnO, for which above-room-temperature operation in THz-QCLs is predicted. Using novel optoelectronic materials like wurzite Zn(Mg)O with no internal fields in the m-plane [10-10] orientation, simplifies the design of any QC structure. After the recent demonstration of intersubband absorption in such m-plane ZnMgO structures, we present the first mid-IR Zn(Mg)O-based QCD with peak responsivity of 0.15 mA/W (77 K) at 3 µm wavelength. The responsivity persists up to 300 K.
In addition, we show first photoluminescence measurements from m-plane Zn(Mg)O THz-QCL structures, emitting at ~4.8 THz at liquid-nitrogen temperatures.
Exploiting intersubband transitions in Ge/SiGe quantum cascade devices provides a way to integrate terahertz light emitters into silicon-based technology. To date all electroluminescence demonstrations of Si-based heterostructures have been p-type using hole-hole transitions. In the pathway of realizing an n-type Ge/SiGe terahertz quantum cascade laser, we present electroluminescence measurements of quantum cascade structures with top diffraction gratings. The devices for surface emission have been fabricated out of a 4-well quantum cascade laser design with 30 periods. An optical signal was observed with a maximum between 8-9 meV and full width at half maximum of roughly 4 meV.
Superfluorescence is a many-body collective coupling phenomenon, where coherence is established through spontaneously triggered correlations of quantum fluctuations from initially fully uncorrelated excited emitters. Here, we investigate densely packed cuboidal arrays of fully inorganic cesium lead halide perovskite quantum dots, known as superlattices and we observe key signatures of superfluorescence: A more than twenty-fold accelerated radiative decay with dynamically red-shifted emission, photon bunching, extension of the first-order coherence time and an intensity-dependent time delay after which the photon burst is emitted. Also, at high excitation density, the superfluorescent decay exhibits a Burnham-Chiao ringing behavior, reflecting the coherent Rabi-type interaction.
References:
Rainò, G.; Becker, M.A.; Bodnarchuk, M.I.; Mahrt, R.F.; Kovalenko, M.; Stöferle, T.; Nature, 563, 671-675, (2018)
The first periodic table published by D. I. Mendelejeev in 1869 based on atomic masses and had empty positions that paved the way for the discovery of several new elements. With the discovery of Pu by Glenn Seaborg as a transuranium element a worldwide race for synthesis of new elements started, mostly at LBNL (Berkeley, USA) and JINR (Dubna, Russia), later also at GSI (Darmstadt, Germany) and at RIKEN (Japan). Currently, 118 elements are known and approved by IUPAC. The heaviest is Oganesson completing the 7th period of the periodic table. While all elements up to Md have been discovered by chemists, heavier ones were found in physics experiments. Chemical experiments have so far reached atomic number 114 (Fl). Efforts are actually made to extend the periodic table into the 8th period starting with element 119. The ultimate limit of the periodic table is predicted at atomic number 172 being the heaviest element with a stable electron shell structure.
The question of the origin of the elements of the Mendeleev table has triggered many lively discussions in the first part of the twentieth century. Some researchers thought that all the elements were produced during the early phase of the evolution of the Universe, while others had the opinion that the stars were the cauldrons in which all the nuclear cooking occurred. I shall explain why neither of these views was correct and how it was possible to make progresses in our understanding. I shall then continue by reviewing the physical principles that govern the evolution of stars and by describing the main nucleosynthetic events at the origin of the elements up to iron. I shall then illustrate the whole process of studying the origin of one element by focussing on the case of oxygen. I shall remind the first ideas about the nuclear processes involved, the astrophysical sites, how this knowledge can be used to make models for the chemical evolution of galaxies and how the predictions of these models can be compared with observational constraints. I shall conclude by describing a present-day highly debated question concerning this element: what is the abundance of oxygen in the Sun?
The build-up of elements up to Fe in stars is governed by fusion reactions in stellar burning stages. The sequence of burning stages is led by the principle that ashes of the previous stage become the fuel of the following one. After the depletion of one fuel, not permitting anymore to make up for the continuing radiation losses which make stars shining, contraction sets in, leading to a temperature increase via the gain of gravitational binding energy. This continues until temperatures pass a threshold, permitting the fusion of reacting charged particles and nuclei via velocities (kinetic energies) which can overcome the repelling Coulomb forces. This stabilizes the star for the next burning stage until its fuel is also depleted. This sequence of events continues until nuclei with the highest binding energy per nucleon are reached, i.e. isotopes of Fe and Ni. What options remain to produce heavier nuclei ? Neutrons do not experience repelling Coulomb forces and neutron capture on nuclei can take place for any temperature. With sufficient amounts of neutrons available, heavy nuclei can be produced by a sequence of neutron captures and beta-decays up to the heaviest nuclei known in nature. The question is how such amounts of unstable neutrons can be provided in stellar environments. The answer is, either (a) via neutron-producing reaction in stellar evolution, or (b) in explosive events originating under conditions of highest densities, where capture of electrons (with high Fermi energies) on protons produced ample amounts of free neutrons. We will connect this to He-burning in stars, as well as neutron star mergers (only observed recently) and a rare class of supernovae.
The development of methods for coherent manipulation of single isolated molecules has made rapid progress in recent years with exciting applications in the fields of precision spectroscopy, fundamental-physics-theories tests, atomic clocks and quantum-controlled chemistry.
In this talk, I will describe our advances for achieving quantum control over a single molecule. In our experiment, a molecular beam is overlapped with a radio-frequency ion trap. We ionize nitrogen ($\textrm{N}_2$) molecules into a specific rotational-vibrational state. The molecular ion is co-trapped with an atomic ion for ground-state cooling and for molecular-state detection by entangling the molecular state with the atomic-ion motion.
While we use $\textrm{N}_2^+$ as a prototype molecule, our methods can be extended to a general class of diatomic and polyatomic molecules.
Atom interferometry has proven within the last decades its surprising versatility to sense with high precision tiniest forces. In this talk I will give an overview of our recent work using an optical cavity enhanced atom interferometer to sense with gravitational strength for fifths forces [1] and for an on the first-place counter-intuitive force due to blackbody radiation[2,3].
[1] M. Jaffe et al., Testing sub-gravitational forces on atoms from a miniature, in-vacuum source mass, Nat. Phys. 13 (2017) 938-942.
[2] P. Haslinger et al., Attractive Force on Atoms due to Blackbody Radiation, Nat. Phys. 14 (2018) 257–260.
[3] M. Sonnleitner et al., Attractive Optical Forces from Blackbody Radiation, PRL 111 (2013) 023601.
We present the novel Long-Baseline Universal Matter-wave Interferometer (LUMI) in Vienna, a near-field, Kapitza-Dirac-Talbot-Lau type interferometer designed for quantum interference of high-mass molecules. It improves on an earlier Kapitza-Dirac-Talbot-Lau interferometer [1] by a factor of 10 in length and a factor 100 in inertial force sensitivity.
The modular design of the experiment permits the in-vacuum exchange between optical and material diffraction gratings as well as the introduction of electric and magnetic fields, collision cells or spectroscopy lasers to explore the electronic, optical, magnetic and structural properties of a very diverse class of particles. We discuss new experiments with atoms, complex molecules and future prospects for high-mass clusters with improved precision over previous devices.
[1] S.Gerlich et al., Nat.Phy.3, 711-715 (2007)
We are developing a highly compact and high-performance vapor-cell atomic clock operating in time-domain Ramsey scheme [1]. Here, we present an analysis of the dominant contributions to the clock instability at the level of 10$^{-14}$, on long-term timescales up to one day. Main limitations arise from light-shift effects, the barometric effect (i.e. the sensitivity to environmental pressure variations), and microwave power-shift effects. The full detailed instability budget will be discussed at the conference. The clock reaches a measured instability of <2x10$^{-14}$ at one day.
[1] S. Kang, et al., Journal of Applied Physics 117, 104510 (2015).
The quantum-to-classical transition is one of the great frontiers of pure physics research. Generating large and long-lived entanglement is a path to exploring it. To reach this path we are using large ensembles of rare-earth ions doped into transparent crystals. Due to their appealing optical and microwave transitions, combined with unparalleled coherence properties, they have been a strong candidate for studying macroscopic entanglement. Here, we try to push the “macroscopicity” of the entangled state, both in atom number and coherence time, by spin-squeezing a large ensemble of Europium ions doped into Y2SiO5. To achieve this, we implement quantum non-demolition measurements on our solid-state system, using a frequency-domain optical interferometer. The generated spin-squeezed states will also be invaluable to quantum sensing.
Levitodynamics, studying the dynamics of levitated massive particles in vacuum, is currently finding applications in high-end sensing. Within fundamental physics, investigating quantum mechanics or thermodynamics at the mesoscale are driving forces of the emerging field. All these areas of levitodynamics rely on tightest control over the center-of-mass (c.m.) motion of the particle.
Here, we experimentally realize [1] cavity cooling of all three c.m. motional degrees of freedom of a levitated nanoparticle in vacuum. The particle is trapped in an optical tweezer and is cooled by coherently scattering tweezer light into the cavity mode. We discuss [2] methods, limits, and opportunities of our approach.
[1] Phys. Rev. Lett. 122, 123601 (2019)
[2] arXiv:1902.01282 (2019)