We investigate a homogeneous system of dipolar bosons in 2D including a short-range repulsion. Varying the strength of this repulsion and the angle of the dipoles with respect to the 2D plane, we find strong evidence for the formation

of a striped and self-bound state in the form of a diverging peak at finite wave vector in the structure factor. We employ the variational

hypernetted-chain...

We present our studies on polarons in a strongly interacting mixture formed by bosonic 41K impurities immersed in a Fermi sea of ultracold 6Li atoms, investigated by means of radio-frequency spectroscopy. The impurities can be either a thermal cloud or a partial Bose-Einstein condensate. The polaron energy for both the thermal cloud and the thermal part of the partial condensate can be...

We report on the realization of a novel, strongly interacting degenerate Fermi-Fermi mixture, which is a promising system for creating a mass-imbalanced fermionic superfluid. The mixture is brought into the deeply degenerate regime at low magnetic field: A narrow-line laser cooling stage allows for an optimization of the starting conditions for the subsequent evaporative cooling. We found a...

We report on the observation of confinement-induced resonances (CIRs) for strong zero-dimensional (0D) confinement in a three-dimensional (3D) optical lattice potential. Starting from a Mott-insulator state with mainly single-site occupancy, we detect loss and heating features at specific values for the confinement length scale and the 3D scattering length. Two independent models, describing...

In our current experiments we are focusing on the dynamics of an impurity subjected to a uniform velocity in a highly confined and correlated system. If the initial velocity of the impurity is above the super sonic value the final velocity is not constant but rather displays a small oscillation. These unexpected dynamics have been coined quantum flutter in previous publications [2,3]. Here we...

Topological pumps allow robust quantized transport of particles in periodic potentials. Their topological origin is analogous to the quantum Hall effect. In atomic physics, ultracold atoms in optical lattices are versatile systems to observe such effects. Yet, charge pumping has been limited to super-lattices operating with a sliding potential. Here, we experimentally realize a topological...

The time evolution of a quantum system can be strongly affected by dissipation. In our experiment, we study a Bose-Einstein Condensate coupled to a high finesse resonator. The cavity mode is populated via the atoms, such that the sum of the coupling beam(s) and the intracavity standing wave gives an optical lattice potential. When the dissipative and the coherent timescales are comparable, we...

We consider a V-shaped three-level system coupled to orthogonal quadratures of a dissipative cavity field, and observe a significant multistability of states with inverted atomic population. The stability of these inverted states are closely related to properties of dark states, and is a combined result of the cavity dissipation and the underlying SU(3) symmetry of the atomic subsystem. The...

Quantum emitters forming nanoscopic polygon shaped arrays posses sub-radiant states with an exciton lifetime growing exponentially with emitter number. Placing an extra resonant dipole as absorber at the ring center creates a highly efficient single photon antenna. Interestingly for exactly nine emitters in a nonagon, as it appears in a biological light harvesting complex LHC2, we find a...

Semiconductor quantum dots are bright, on-demand single photon sources to realise quantum communication devices. An important requirement to realise such devices is the high-fidelity preparation of the biexciton state since the subsequent radiative decay produces entangled photon pairs. Although resonant excitation to the biexciton state has been successful, its sensitivity to the excitation...

We present resonant tunneling diodes, which feature intersubband transitions that are strongly-coupled to the cavity field. By using double-metal cavities with different resonant frequencies we show the infamous avoided-crossing property of the intersubband polaritons.

Resonant tunneling diodes are ideal systems for investigating resonant electronic transport in systems, which are...

Optical antennas have been widely used for manipulating light-matter interactions at the nanoscale in order control the emission intensity and directivity of single molecules. However, to date, precisely controlling the interaction between molecules and antennas at the single level is still challenging. In this contribution, we exploit the DNA origami technique to self-assemble ultra-compact...

Nonlinear optical processes are widely used in quantum communication and computation, as well as laser engineering. In particular, difference frequency generation can be utilized to erase spectral distinguishability between single photons or generate laser light in otherwise hard to reach wavelength regimes. In this work, we present an AlGaAs Bragg-reflection waveguide with an embedded...

We explore the evolution of the electronic spectrum of potassium compounds isolated in helium droplets from single atoms and molecules up to nanosized clusters, using a novel combination of experimental methods. The employment of a time of flight mass spectrometer enables the spectroscopy of atomically precise potassium clusters up to K_{110}. Spectra for larger clusters within a...

Semiconductor lasers with ultra-low thresholds and minimal footprints are of great interest. For high-reflectivity-coated ridge-lasers, a low threshold can only be achieved by suppressing the diffraction losses arising at laser facets. We show that, counter-intuitively, opening a carefully designed aperture in a metallic facet coating can simultaneously enhance both its transmission and modal...

High harmonic generation in a noble gas target is the most common method for table top generation of coherent XUV light. We discuss the recent progress and perspectives of high harmonic generation driven directly inside the cavity of an ultrafast thin-disk laser oscillator. Our laser system operates at a record high intracavity performance of any laser oscillator with > 1 GW of peak power, > 1...

We developed a spectroscopy method for quantum sensing based on sequential weak measurements to detect the free-induction decay (FID) signal of a single carbon-13 nuclear spin. We showed that such measurements mitigate the unwanted quantum back-action, and provide a number of further advantages, including a large frequency bandwidth and possibility of efficient Fourier Nuclear Magnetic...

The Coupled Dark State Magnetometer is a scalar magnetometer based on coherent population trapping within the ^{87}Rb D_{1} line, which is especially designed for scientific space missions. It is developed in a cooperation between the Institute of Experimental Physics of Graz University of Technology and the Space Research Institute of the Austrian Academy of Sciences.

The...

We discuss quantum variational optimization of Ramsey interferometry with ensembles of N-entangled atoms, and its application to atomic clocks based on a Bayesian approach to phase estimation. We identify best input states and generalized measurements within in form of entangling and decoding quantum circuits. These circuits are built from basic quantum operations available for the particular...

Frequency dissemination in phase-stabilized optical fiber networks for metrological frequency comparisons and precision measurements are promising candidates to overcome the limitations imposed by satellite techniques. However, network constraints restrict the availability of dedicated channels in the commonly-used *C-band*. Here, we demonstrate the dissemination of an SI-traceable ultrastable...

We present a study of the Rydberg spectrum in $^{166}$Er for series connected to the $4f^{12}(^3H_6)6s$, $J_c=13/2$ and $J_c=11/2$ ionic core states using an all-optical detection based on electromagnetically induced transparency in an atomic beam. Identifing approximately 550 states, we find good agreement with a multi-channel quantum defect theory (MQDT) which allows assignment of most...

Ultra-narrow atomic transitions have been extensively used for high-precision measurements and for the manipulation of quantum systems.

Here, we report on the observation of a narrow inner-shell orbital transition of erbium at 1299.21nm, and, for the first time, on coherent control of the atomic state with this optical transition. High-resolution spectroscopy is performed on five erbium...

Positronium is an excellent system to test bound state QED theory to very high precision, since it is almost exlusively governed by the electro-magnetic force and does not exhibit finite size effects. Numerous precise experiments have therefore been conducted in the past to measure the fine and hyperfine splitting. However, some experiments show disagreements of up to 4.5σ with most recent...

We are building a cryogenic hydrogen (H) beam and pulsed ultraviolet laser detection system for the first demonstration of Quantum Gravitational States (QGS) of atoms. The enhanced statistics available through use of hydrogen atoms versus ultracold neutrons will increase sensitivity to short-range forces predicted in extensions of the Standard Model that would alter these states. Additionally,...

We report on measurements of the anisotropic dynamical polarizability of Dy on both sides of the 626-nm intercombination line, employing modulation spectroscopy in a one-dimensional optical lattice. To eliminate large systematic uncertainties, we use K as a reference species with accurately known polarizability. Our derived natural linewidth is in excellent agreement with literature values,...

We present the first experimental realization of Bragg diffraction for polar and non-polar molecules [1]. Using a thick laser grating at 532 nm, we diffract a molecular beam and observe Bragg diffraction in the far-field. We study this effect for the dye molecule phthalocyanine and the antibiotic ciprofloxacin and observe a pronounced angular dependence and asymmetry in the pattern,...

Vienna’s Long-Baseline Universal Matter-wave Interferometer (LUMI) has successfully demonstrated interference of massive molecules consisting of up to 2000 atoms and with masses up to 28.000 amu. LUMI’s high force sensitivity of $10^{-26}$ N has also been used to sense electronic, optical, magnetic and structural properties of a very diverse class of particles. For example, measuring the...

The phenomenon of the Quantum Cheshire Cat is a paradoxical effect in which different properties of a particle seem to be spatially separated. To observe the effect, weak disturbances are applied in between the pre and postselection procedure in an interferometer setup. One may perform weak measurements and use weak values to quantify the perceived path occupations of the properties. Some...

Many of the breakthroughs in quantum science and technology rely on engineering strong Hamiltonian interactions between quantum systems. Typically, strong coupling relies on short-range forces or on placing the systems in high-quality electromagnetic resonators, which restricts the range of the coupling to short distances. We show how a loop of laser light can generate Hamiltonian coupling...

Owing to its excellent isolation from thermal environment, an optically levitated silica nanoparticle in ultra-high vacuum is a strong candidate to observe quantum behavior of massive objects at room temperature, with applications ranging from sensing to testing fundamental physics. With the help of a new, non-standard cavity interaction – cavity cooling by coherent scattering – we have...

Gravity continues to pose some of the most outstanding open problems to modern physics: it remains resistant to unification within the standard model and its underlying concepts appear to be fundamentally disconnected from quantum theory.

Thus far, testing gravity involves mainly macroscopic masses on the kg-scale and beyond. Here we show gravitational coupling between two gold spheres of 1...

It is unclear how our classical world emerges from the quantum world. It is also unclear how to incorporate effects of gravity into quantum mechanics. To get experimental insights into these problems, we need to prepare larger masses in quantum states.

Magnetically-levitated superconducting microparticles make promising systems for doing this. We work with a lead microsphere of ~10^18 amu...

Quantum tunneling reactions can play a significant role in chemistry, and hydrogenic systems allow for first-principles calculations. The rate of the tunneling reaction H$^2$ + D$^- \rightarrow$ HD + H$^-$, for which the collision complex is closely related to the H$^-_3$ anion, has been calculated but has lacked verification. Here we present high-sensitivity measurements of the reaction rate...

Tracing ultrafast processes induced by interaction of light with matter is often very challenging. In molecular systems, the initially created electronic coherence becomes damped by nuclear rearrangement on a femtosecond timescale which makes observations of electron dynamics in molecules particularly difficult. We demonstrate that the attosecond transient absorption spectroscopy (ATAS) can be...

The main goal of the project is to find a machine learning approximation for the kinetic energy functional of orbital-free density functional theory,

\begin{equation}

T[n] = \int \tau[n] \,\mathrm{d}x,

\end{equation}

where the function $\tau[n]$ is represented using a feed forward neural network. Since it is known that the function $\tau$ is translationally invariant and non-local,...

Quantum chemistry has become an important tool to analyze and predict the properties of molecules. Coupled cluster (CCSD(T)) is considered to be the gold standard as it gives accurate results and can be improved in a well-known manner, but is computationally expensive. If one wants to compute the properties of molecules containing heavy elements relativistic contributions need to be included...

Recently, stacked sheets of nanoporous graphene have been suggested for the separation of racemic mixtures with respect to molecular chirality. Different pore arrangements lead to different barrier heights for the two enantiomers of a given molecule. We are investigating the performance of these membranes via a combination of a recent force-field ansatz of the Grimme group with...

We extend the time-dependent Variational Monte Carlo method to a new way of accessing the dynamic structure factor of strongly correlated one-dimensional bosonic systems in continuous space. In order to extract the response of the system in the form of density fluctuations, we use the stochastic noise inherent to this Monte Carlo simulations. We present the details of the method and show the...