Hydrodynamic instabilities in classical fluids, often characterized by the exponential growth of a well-defined pattern, are encountered in many mundane situations: the development of ocean waves, the periodic array of water droplets in a spider web or the mushroom-like clouds resulting from volcano eruptions are all examples of such instabilities. Increasing our understanding of the...
Atoms are employed as highly sensitive sensors in a wide range of applications, including metrology, precision gravimetry, and magnetometry. Atom lasers offer a compelling platform for mapping fields due to their large sampling area, tunable accelerations, and high atomic sensitivity.
In our work, we have conducted a series of experiments investigating the interaction of atom lasers with...
We utilize the rapidly developing capabilities of atom tweezer arrays to advance the studies of quantum optics, open quantum mechanics, and cavity QED. Single atoms in optical tweezers are used as scanning-probe microscopes to map out the structure of optical cavity modes.
We demonstrate rapid, high-fidelity, mid-circuit readout of an atom tweezer array using cavity-enhanced optical...
Understanding many-body systems far-from equilibrium is an outstanding challenge in physics. It was proposed that such systems generically feature universal dynamic scaling while approaching non-thermal fixed points; the associated dynamical scaling exponents would provide a classification of the nonequilibrium phenomena analogously to the equilibrium universality classes. First evidence for...
First, I will discuss the new possibilities that bulk molecular Bose-Einstein condensates may open up for dipolar many-body physics in the near future. Building on our work on dipolar droplets and supersolids that form from weakly dipolar atoms, I will show how ultracold molecules and microwave shielding can provide fundamentally new insights into these exotic states of matter. Second, I will...
We experimentally realize various dynamical phases such as a dissipative discrete time crystal [1], dynamical bond density wave phase [2-4], and limit cycle phase [5]. Our setup consists of a Bose-Einstein condensate of $^{87}$Rb atoms overlaps with a single mode optical cavity. The key feature of the cavity is a very small field decay rate ($\kappa / 2\pi$ = 3.6kHz), which is in an order of...
We study quantum many-body dynamics after a quantum quench in systems of optical lattices loaded with ultracold Bose gases, which can be quantitatively described by the Bose-Hubbard model. We focus on two kinds of dynamics, namely, spreading of spatial correlations and non-ergodic dynamics associated with the Hilbert space fragmentation. For the former case, we start with a Mott-insulating...
Supersolidity is an exotic phase of quantum matter which combines the characteristics of a superfluid with the crystalline spatial structure of a solid, resulting from the spontaneous breaking of both $U(1)$ phase symmetry and translational invariance. In spin-orbit-coupled Bose-Einstein condensates (SOC BECs), a spatially modulated density profile in the form of stripes emerges from the...
Hydrodynamics provides a successful framework to effectively describe complex many-body phenomena by coarse graining over microscopic constituents yielding macroscopic quantities. The requirement on the number of averaged microscopic particles is an outstanding question in various fields, ranging from nuclear to high energy physics.
Here, we challenge this condition by using few strongly...
Recent experiments with ultracold atoms in tilted optical lattices demonstrated unconventional relaxation dynamics of far-from-equilibrium initial states. Instead of the conventional diffusive relaxation, excitations decay only subdiffusively in these systems or may even come to a full stop. Here, we discuss how these observations can be understood by emergent fracton constraints. These...
Engineering long-range interactions in cold-atom quantum simulators can lead to exotic quantum many-body behaviour, becoming and enabling tool in the simulation of relevant problems in condensed matter or quantum chemistry [1]. In addition to recent efforts with bosonic species [2,3], fermionic atoms in ultracold atomic mixtures can also act as mediators. This gives rise to long-range...
Although non-local interactions characterize a variety of experimental setups their full control remains challenging. In this talk I will discuss two novel schemes where non-local interactions can be engineered and naturally put into competition with geometrical frustration. The first scheme is based on Cesium atoms trapped in a one-dimensional optical lattice at the anti-magic wavelength....
One of the most important challenges for fermionic systems in optical lattices is the quest for low temperatures. Only at temperatures below a few percent of the Fermi temperature, correlation lengths become sizeable. This is the regime in which the system behaves highly collective, and where new quantum phases are expected to emerge. Despite significant progress in recent years, the required...
Ultracold polar molecules promise a wide range of exciting new opportunities for quantum information processing, quantum simulations, cold chemistry, and precision measurements. I will present how microwave (MW) shielding of ground-state NaK molecules stabilizes collisions allowing us to evaporate dipolar molecules in 3D to quantum degenerate temperatures of 0.36 times their Fermi temperature....
Our group is studying the unique features of lanthanide atoms, such as dysprosium, for molecular quantum science.
We are building a new apparatus for controlling ultracold reactions between dysprosium atoms and dimers using an optical cavity. We report on the realization of a MOT of dysprosium and how we plan to achieve a molecular BEC.
On the side, we are exploring the optical spectra of...
The Fermi polaron, a particle dressed by excitations of a fermionic medium, has been extensively studied in ultracold atomic gases. Recently, it was realised that the optical response of doped atomically thin semiconductors also corresponds to a quantum impurity problem, where excitons are introduced into an electronic medium. I will discuss three scenarios where we have recently used...
We investigate the Fermi-Hubbard model with a Floquet-driven impurity in the form of a local time-oscillating potential. For strong attractive interactions a stable formation of pairs is observed. These pairs show a completely different transmission behavior than the transmission that is observed for the single unpaired particles. Whereas in the high-frequency limit the single particles show a...
Mixtures of Bose-Einstein condensates offer situations where the usually dominant mean-field energy in weakly interacting systems can be reduced such that higher-order (for example beyond-mean-field) terms may play a dominant role in the equation of state. In this context, the case of coupled two-component $^{39}$K Bose-Einstein condensates is specifically addressed. First, large attractive...
In quantum mechanics, collisions between two particles are captured by an energy-dependent scattering matrix describing the transfer from an initial entrance state to an outgoing final state. The scattering matrix can be analytically extended to a plane of non-physical complex energies where, remarkably, poles of this continued S-matrix will be intimately related to scattering resonances of...
Kinetic frustration is opening a new paradigm in cold atomic systems, as it induces non-trivial magnetic and spin-charge correlations at temperature scales of the order of the tunneling strength. This phenomenon appears in the strongly interacting regime of doped Fermi- and Bose-Hubbard Hamiltonians in non-bipartite lattices, such as the two-dimensional triangular lattice, and bipartite...
Conventional superconductivity emerges from pairing of charge carriers mediated by phonons. In many unconventional superconductors, the pairing mechanism is conjectured to be mediated by magnetic correlations, as captured by models of mobile charges in doped antiferromagnets. However, a precise understanding of the underlying mechanism in real materials is still lacking and has been driving...
Heat engines convert thermal energy into mechanical work both in the classical and quantum regimes. However, quantum theory offers genuine nonclassical forms of energy, different from heat, which so far have not been exploited in cyclic engines. We here experimentally realize a novel quantum many-body engine fuelled by the energy difference between fermionic and bosonic ensembles of ultracold...
For the past two decades harmonically trapped ultracold atomic gases have been used with great success to study fundamental many-body physics in flexible experimental settings. However, the resulting gas density inhomogeneity in those traps makes it challenging to study paradigmatic uniform-system physics (such as critical behavior near phase transitions) or complex quantum dynamics.
The...
We explore the interaction between two trapped ions mediated by a surrounding quantum degenerate Bose or Fermi gas. Using perturbation theory valid for weak atom-ion interaction, we show analytically that the interaction mediated by a Bose gas has a power-law behavior for large distances whereas it has a Yukawa form for intermediate distances. For a Fermi gas, the mediated interaction is given...
Weakly interacting quantum gases offer a very convenient platform for the study of superfluid dynamics. One of the many intringuing properties of superfluids is their behavior in the presence of an imposed rotation. At zero temperature, the ground state of the rotating gas supports a triangular vortex lattice, the vortex density being set by the rotation frequency. As temperature increases,...
For a thorough investigation of both elastic and inelastic three-body interactions, ranging from universal Efimov physics to non-univeral species-dependent collisions, one needs a three-body collision model that can handle all regimes of interaction strength. We developed a full three-body spin-dependent coupled-channels model in momentum space, with a very accurate expansion of the full...
Photon-mediated interactions between atoms coupled to an optical cavity are emerging as a powerful tool for engineering entangled states and many-body Hamiltonians. In a next-generation cavity QED (CQED) experiment currently approaching completion at LKB, we combine a strong-coupling fiber Fabry-Perot microcavity with state-of-the-art atomic tweezer techniques for single-atom addressing and...
I will discuss the presence of non-ergodic extended states in many-body interacting systems in disorder. Our preliminary calculations indicate that these novel states can be present in the one-dimensional Hubbard model with on-site disorder for two-component fermions. These calculations rely on exact diagonalization and are able to provide results only for fairly small systems, namely up to 24...
We envision a hybrid quantum network of individually trapped polar molecules interfaced with Rydberg atoms. The nodes of the network are single molecules, where information is stored. The links are Rydberg atoms which mediate strong, long-range interactions between nodes. This hybrid network leverages the long-lived internal states of molecules and the strong interactions provided by Rydberg...
We demonstrate that the one-axis twisting (OAT), a versatile method of creating nonclassical states of bosonic qubits, is a powerful source of many-body Bell correlations. We develop a fully analytical and universal treatment of the process, which allows us to identify the critical time at which the Bell correlations emerge and predict the depth of Bell correlations at all subsequent times....
I will present three of our latest results on atomic quantum gases with engineered dissipation. This includes a joint work with the group of Artur Widera, where we investigate a phase transition in time during the transient relaxation dynamics of an open quantum systems [1], concepts for controlled state preparation using quantum feedback control in atomic cavities [2], as well as ideas...
We investigate the induced Casimir interaction between two impurities in superfluid atomic gases. With the help of effective field theory (EFT) for a Galilean invariant superfluid, we find that the induced impurity-impurity potential at long distance does not fall off exponentially as a Yukawa potential, but instead exhibits a universal power-law scaling. We show that the exchange of two...
Strongly correlated fermionic matter is at the heart of many open questions in quantum science, ranging from electon-Volt scale problems in condensed matter physics to Giga-electon-Volt dynamics in heavy ion collisions. Ultracold fermionic atoms are a unique platform, where the dynamics of interacting fermions can be probed using time- and particle-resolved correlation measurements.
In...
Supersolidity has recently been discovered in ultra-cold dipolar Bose gases. This intriguing state of matter is characterized by the spontaneous and simultaneous breaking of phase and translational symmetry, resulting in the non-intuitive coexistence of superfluid and crystalline features.
One of the fundamental characteristics of superfluidity is the existence of quantized vortices....
Ultracold atoms in triangular optical lattices are a versatile platform to study strongly correlated systems in which exotic states of matter appear due to the interplay between charge and magnetic order. Large degeneracies in the many-body ground state of triangular lattices could result in a quantum spin liquid that has been numerically predicted to appear between the metallic and...
When charged particles are placed in a magnetic field, the single-particle energy states form discrete, highly-degenerate Landau levels. Since all states within a Landau level have the same energy, the behaviour of the system is completely determined by the interparticle interactions and strongly-correlated behaviour such as the fractional quantum Hall effect occurs. Here, we present recent...
Central spin models, where a single spinful particle interacts with a spin environment, find wide application in quantum information technology and can be used to describe, e.g., the decoherence of a qubit over time. We propose a method of realizing an ultracold quantum simulator of a central spin model with XX (spin-exchanging) interactions. The proposed system consists of a single Rydberg...
Due to advances in ultracold gas experiments and the recent unexpected discovery of superconductivity in magic-angle twisted bilayer graphene and other moiré materials, much effort is currently being devoted to understand superconductors and superfluids in the strongly correlated regime characterized by electronic energy bands with very small, or even vanishing, bandwidth. According to...
Anyons are particles with exchange statistics that are neither bosonic nor fermionic, but that interpolate between these two limits. We realize a one-dimensional Anyon-Hubbard model (AHM) with ultracold Rubidium 87 atoms in an optical lattice. To engineer the desired Hamiltonian, we use a novel three-tone lattice amplitude modulation technique that allows us to tune the exchange phase of two...
Finite temperature damping of rotons in elongated Bose-condensed dipolar gases which are in the Thomas-Fermi regime in the tightly confined directions, is discussed. The presence of many branches of excitations which can participate in the damping process is shown to result in significant increase of the damping rate. It is found, however, that even rotons with energies close to the roton gap...
We study driven atomic Josephson junctions realized by coupling two two-dimensional atomic clouds with a tunneling barrier. By moving the barrier at a constant velocity, dc and ac Josephson regimes are characterized by a zero and nonzero atomic density difference across the junction respectively. Here, we monitor the dynamics resulting in the system when, in addition to the the above...
The demanding experimental access to the ultrafast dynamics of materials challenges our understanding of their electronic response to applied strong laser fields. In this work, we show that trapped ultracold atoms with highly controllable potentials can become an enabling tool to describe phenomena in a scenario where some effects are more easily accessible and twelve orders of magnitude...
Bright solitons in atomic Bose-Einstein condensates are strong candidates for high precision matter-wave interferometry, as their inherent stability against dispersion supports long interrogation times. An analog to a beam splitter is then a narrow potential barrier. A very narrow barrier is desirable for interferometric purposes, but in a typical realization using a blue-detuned optical...
We employ spectroscopic tools to study interactions and emergent order in an ultracold mixture of a Bose-Einstein Condensate (BEC) and spin-polarized Degenerate Fermi Gas (DFG). We characterized the effect of fermion-mediated interaction on the boson clock transition [1]. We now extend our work by tuning the fermion-mediated effect on the Bogoliubov excitation spectrum through a Feshbach...
Following a quick review of the existence of supersolid and melted supersolid phases (hexatic superfluids) in two-dimensional continuum dipolar boson systems [1], the emergence of supersolid phases of dipolar and spin-orbit coupled bosons in optical lattices is discussed. For dipolar systems, it is shown that the ground state phase diagram is very sensitive to the direction of an externally...
Optical box traps offer new possibilities for quantum-gas experiments. Building on their exquisite spatial and temporal control, we propose to engineer system-reservoir configurations using box traps, in view of preparing and manipulating topological atomic states in optical lattices. First, we consider the injection of particles from the reservoir to the system: this scenario is shown to be...
When s-wave scattering length diverges in the vicinity of Feshbach resonances the system of three particles exhibits bound states characterized by universal properties [1,2]. A well-known fact is that near a narrow Feshbach resonance the existence range of these states shrinks down as a function of the narrowness of the resonance. Empirically, however, this is not the case for bosonic lithium....
Degenerate quantum gases with strong permanent dipole moments are a robust platform for studying anisotropic and long-ranged phenomena in strongly correlated quantum systems [1]. When subjected to a rotating magnetic field, the resulting precession of the dipole moments of a magnetic dipolar Bose-Einstein condensate (dBEC) imparts angular momentum to the system. Due to the superfluidity of an...
General relativity predicts that the curvature of spacetime induces spin rotations on a parallel transported spinful particle. We have deployed Unruh's analogue gravity picture and have considered an ordinary quantised vortex as a charged particle embedded in a two-dimensional scalar Bose--Einstein condensate (BEC). We have shown, backed by direct numerical simulations, that the vortex in a...