Bulletin of the American Physical Society
52nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 66, Number 6
Monday–Friday, May 31–June 4 2021; Virtual; Time Zone: Central Daylight Time, USA
Session C07: Dynamics of Cold Atoms in Optical Lattices ILive
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Chair: Han Pu, Rice University |
Tuesday, June 1, 2021 10:30AM - 10:42AM Live |
C07.00001: Experimental evidence for Hilbert-space fragmentation in tilted Fermi-Hubbard chains Sebastian Scherg, Thomas Kohlert, Pablo Sala de Torres-Solanot, Frank Pollmann, Bharath Hebbe Madhusudhana, Immanuel F Bloch, Monika Aidelsburger Out-of-equilibrium phenomena constitute natural applications of quantum simulators based on ultracold atoms in optical lattices. We utilize them to explore fundamental questions about the thermalization of isolated quantum many-body systems. Generically, thermalization in such systems occurs according to the eigenstate thermalization hypothesis (ETH). In contrast, violation of ETH is believed to occur mainly in two types of systems: integrable models and many-body localized systems (MBL). In between these two extreme limits there is a whole range of models that exhibit more complex dynamics, for instance, due to an emergent fragmentation of the Hilbert space (HSF) into many dynamically disconnected subspaces. We have realized the tilted 1D Fermi-Hubbard model which lies at the interface of MBL and HSF and probe out-of-equilibrium dynamics in this model by preparing an initial charge-density wave state. We observe a robust memory of this initial state over a wide range of parameters. Furthermore, we find a strong initial-state dependent thermalization in the large tilt limit - a smoking-gun signature of Hilbert-space fragmentation. |
Tuesday, June 1, 2021 10:42AM - 10:54AM Live |
C07.00002: Realizing a Fermi gas with strong long-range interactions using Rydberg dressing Elmer Guardado-Sanchez, Benjamin M Spar, Peter Schauss, Ron Belyansky, Jeremy T Young, Przemyslaw Bienias, Alexey V Gorshkov, Thomas P Iadecola, Waseem S Bakr Itinerant quantum gases with strong, long-range interactions can be used for the quantum simulation of many interesting quantum many-body phenomena including quantum magnetism, topological superfluidity and supersolidity. This has spurred the development of various experimental systems with non-local interactions including magnetic atoms and polar molecules, but reaching the regime of non-local interactions strong compared to the kinetic energy has been elusive to date. In this talk, I will present experiments where we induce such interactions in a 2D Fermi gas of lithium-6 atoms using Rydberg dressing. We achieve this by off-resonantly coupling our neutral atoms to a highly excited Rydberg state via a single-photon transition. We measure the interactions using many-body Ramsey interferometry and study the lifetime of the gas in the presence of tunneling, finding that tunneling does not reduce the lifetime. The system is approximately described by a t − V model on a square lattice where the fermions experience isotropic nearest-neighbor interactions and are free to hop only along one direction. To probe the interplay of non-local interactions with tunneling, we investigate the short-time relaxation dynamics of charge density waves in the gas. We find that strong nearest-neighbor interactions slow down the relaxation due to kinetic constraints. Our work opens the door for quantum simulations of other lattice systems with strong non-local interactions such as extended Fermi-Hubbard models. |
Tuesday, June 1, 2021 10:54AM - 11:06AM Live |
C07.00003: Long-lived stripe pattern in tilted optical lattices Henrik P Zahn, Vijay Singh, Luca Asteria, Marcel Kosch, Lukas Freystatzky, Klaus Sengstock, Ludwig Mathey, Christof Weitenberg Tilted lattices show a rich variety of phenomena including Bloch oscillations and Stark localization. In the regime of a bosonic Mott insulator, the system can be mapped to a spin model with an antiferromagnetic ground state corresponding to a charge density wave. Using our new microscopy method, we observe a similar formation of stripe patterns in a weakly-interacting three-dimensional system and extend it to triangular lattices. The stripes correspond to a spontaneous symmetry breaking revealed by the formation of domain walls. Our work sets the stage for the study of general pattern formation and transport in various lattice geometries and inhomogeneous systems. |
Tuesday, June 1, 2021 11:06AM - 11:18AM Live |
C07.00004: Propagation of correlations in the Mott phase of the Bose Hubbard model in dimensions higher than one Malcolm P Kennett, Ali Mokhtari-Jazi, Matthew Fitzpatrick Lieb-Robinson and related bounds set an upper limit on the speed at which information propagates in non-relativistic quantum systems. Experimentally, light-cone-like spreading has been observed for correlations in the Bose-Hubbard model (BHM) after a quantum quench. Using a two-particle irreducible (2PI) strong-coupling approach to out-of-equilibrium dynamics in the BHM we calculate both the group and phase velocities for the spreading of single-particle correlations in one, two, and three dimensions as a function of interaction strength in the Mott insulating phase. Our results are in quantitative agreement with recent measurements of the speed of spreading of single-particle correlations in both the one- and two-dimensional BHM realized with ultracold atoms. We demonstrate that there can be large differences between the phase and group velocities for the spreading of correlations and explore how the anisotropy in the velocity varies across the phase diagram of the BHM. Our results establish the 2PI strong-coupling approach as a powerful tool to study out-of-equilibrium dynamics in the BHM in dimensions greater than one. |
Tuesday, June 1, 2021 11:18AM - 11:30AM Live |
C07.00005: Quantum Gas Microscope of Bosonic Atoms with Tunable Interaction Kiryang Kwon, Kyungtae Kim, Junhyeok Hur, SeungJung Huh, Jae-yoon Choi In this presentation, we report a quantum gas microscope of Lithium-7 atoms in a two-dimensional (2D) square optical lattice. Individual atoms in each lattice site are imaged by Raman sideband cooling in a hybrid potential of the 2D lattice and a single tightly focused optical sheet potential. With a high numerical aperture (NA=0.65) objective, we achieve a point spread function of 600 nm (full width half maximum), which is small enough to resolve the lattice spacing (752 nm). About 3000 photons were collected during 1 s of exposure time with a detection fidelity of 98%. Moreover, using the magnetic Feshbach resonance, we are able to obtain a large size of unity filling Mott insulator containing 1000 atoms. Imaging the atoms in the deep lattice potential with Gray molasses will be also discussed. |
Tuesday, June 1, 2021 11:30AM - 11:42AM Live |
C07.00006: Investigation of Band Structure Topology via Directly Probing a Dirac Point in an Optical Honeycomb Lattice Charles Brown, Shao-Wen Chang, Malte Nils Schwarz, Tsz-Him Leung, Dan M Stamper-Kurn In a system with band structure, a point where two bands become degenerate marks a singularity in the Bloch wavefunction, where it cannot be uniquely determined. Studying such singularities provides a path toward understanding the geometry and topology of the Hilbert space spanned by the Bloch wavefunctions. Several experiments have observed effects of the Abelian Berry connection in a system with a Dirac point (a linear band-touching point), such as the accumulated Berry phase of π after enclosing a Dirac point in a single path-independent loop in quasimomentum. Instead, we study effects of the Berry connection by probing the Dirac point in a new way with a particular set of quasimomentum trajectories. To study this physics, we load a Bose-Einstein condensate into an optical honeycomb lattice with Dirac points, and use feedback control to dynamically translate the lattice in two-dimensions, allowing us to move the atoms along some quasimomentum trajectory. For straight trajectories from zero quasimomentum to the Dirac point, which then turn and exit at some angle, we observe band population transfer that is consistent with non-interacting band-theory. We find that this transfer depends on the exit angle and is independent of the speed (only up to a certain speed) that the trajectory is traversed, indicating that this behavior is the result of band structure topology and not dynamics. |
Tuesday, June 1, 2021 11:42AM - 11:54AM Live |
C07.00007: Observation of stochastic resonance in an optical lattice: Interplay of probe-modified potentials and optical pumping rates Kefeng Jiang, Alexander Staron, Ian T Dilyard, Ajithamithra Dharmasiri, Anthony Rapp, Samir Bali We illuminate cold atoms diffusing around inside a dissipative optical lattice with a weak probe beam and detect the probe transmission spectrum. We find that the probe induces directed propagation of the atoms in a direction perpendicular to the probe propagation, even for probe intensities lower than 1% of the lattice intensity. We observe a resonant enhancement in the directed propagation of the cold atoms as we vary the photon scattering rate. This resonant response of the system (i.e., the atom) as a function of random environmental noise (i.e., photon scattering) is a signature of stochastic resonance. We present a simple one-dimensional model that reveals how the probe-modified ground state lattice potentials and optical pumping rates conspire to produce resonant directed propagation. We also experimentally characterize the stochastic resonance as a function of system parameters such as modulation amplitude and lattice well-depth. |
Tuesday, June 1, 2021 11:54AM - 12:06PM Live |
C07.00008: Observation of confinement-induced resonances in a 3D lattice Deborah Capecchi 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, in isotropic and anisotropic lattice potentials. Two independent models, describing the coupling between the center-of-mass and the relative motion of the particles as mediated by the lattice, predict the resonance positions to a good approximation, suggesting a universal behavior. Our results show that CIRs exist for any dimensionality and open up a new method for interaction tuning and controlled molecule formation under strong 0D confinement. |
Tuesday, June 1, 2021 12:06PM - 12:18PM Live |
C07.00009: NOON states with ultracold bosonic atoms via resonance- and chaos-assisted tunneling Guillaume Vanhaele, Peter Schlagheck We investigate theoretically the generation of microscopic atomic NOON states, corresponding to the coherent |
Tuesday, June 1, 2021 12:18PM - 12:30PM Live |
C07.00010: Quantum speed limits crossover probed by matter wave interferometry Gal Ness, Manolo Rivera Lam, Wolfgang Alt, Dieter Meschede, Yoav Sagi, Andrea Alberti Quantum speed limits dictate the rate of quantum state evolution and thus restrict the maximal performance of any quantum technology. The two most celebrated limits are formulated in terms of the state's energy uncertainty (Mandelstam-Tam bound) and average energy (Margolus-Levitin bound). We perform matter wave interferometry experiments and track the motion of a single atom in a spin-dependent lattice. This setup constitutes an open multi-level quantum system in which we test the speed limits. Our results show that only the combination of the two limits provides the relevant bound. Specifically, we find that at short evolution times, the Mandelstam-Tam limit is always the tighter bound. A crossover to the Margolus-Levitin limit may occur at longer times, depending on the ratio between the first two energy moments. Our work elucidates the role of each quantum speed limit and establishes matter wave interferometry as a powerful tool to study fast quantum state dynamics. |
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