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 S06: Quenched atomic gasesLive
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Chair: Bhuvanesh Sundar, U Colorado |
Thursday, June 3, 2021 10:30AM - 10:42AM Live |
S06.00001: Non-Equilibrium Dynamics of Trapped Fermi gases with Time-Dependent interactions: Consequences of Conformal Symmetry and Power-Law Damping Jeff A Maki, Shizhong Zhang, Fei Zhou Conformal symmetry greatly restricts the dynamics of scale invariant quantum gases. This symmetry is extremely important as it can preclude entropy production. The absence of entropy production for scale invariant gases can be readily detected in undamped large amplitude oscillations in quenched harmonic traps. Away from resonance there will be damping due to the broken conformal symmetry, which depends not only on the nearby scale invariant point but also the time-dependence of the scale breaking interactions. The time-dependent scale breaking interactions allow one to tune the non-equilibrium signatures of broken conformal symmetry, and can even lead to power-law damping of the the large amplitude oscillations.. |
Thursday, June 3, 2021 10:42AM - 10:54AM Live |
S06.00002: Quench dynamics of one dimensional Bose polarons Jonas Jager, Ryan Barnett We consider the dynamics of a quantum impurity after a sudden interaction quench into a one-dimensional degenerate Bose gas. We use the Keldysh path integral formalism to derive a truncated Wigner like approach that takes the back action of the impurity onto the condensate into account already at the mean-field level and further incorporates thermal and quantum effects up to one-loop accuracy. This framework enables us to obtain the real space trajectory of the impurity as well as the impurity Green's function and the absorption spectrum of the polaron. We find that quantum corrections and thermal effects play a crucial role in the impurity momentum and the impurity Green's function at weak to intermediate impurity-bath couplings. We also observe the broadening of the absorption spectrum with the increasing temperature. |
Thursday, June 3, 2021 10:54AM - 11:06AM Live |
S06.00003: Observation of quasiparticle pair-production and quantum entanglement in atomic quantum gases quenched to an attractive interaction Cheng-An Chen, Sergei Khlebnikov, Chen-Lung Hung Coherent pair-production processes are enabling mechanisms for quantum entanglement generation in continuous variable states. In this talk, we present an experimental scheme to initiate pair-production of quasiparticles in atomic quantum gases by quenching to an attractive interaction. We characterize non-classical correlation in quasiparticles by quenching the atomic interaction back to repulsive, and by monitoring the in situ density noise power spectrum, which effectively measures a homodyne interference between ground state atoms and quasiparticles of opposite momenta. We observe large amplitude growth in the power spectrum and subsequent coherent oscillations in a wide spatial frequency band, demonstrating coherent quasiparticle generation and evolution. The spectrum is observed to oscillate below a limit set by the Peres-Horodecki separability criterion of continuous-variable states, thereby confirming quantum entanglement between interaction quench-induced quasiparticles. |
Thursday, June 3, 2021 11:06AM - 11:18AM Live |
S06.00004: Implosions in Bose Einstein Condensates as a probe for quantum and thermal fluctuations Michael J Van de Graaff, Eli J Halperin, John L Bohn, Jun Ye, Eric A Cornell Understanding the nature of fluctuations within a Bose-Einstein Condensate poses a difficult experimental challenge. When a BEC initially with positive interactions is quenched to a large negative scattering length, it is known that the resulting gas will be unstable and begin to collapse. Any initial perturbations of the density will be amplified as they seed the ensuing implosions. Using a well understood initial perturbation provided by an optical lattice potential, we characterize the experimental signatures of the microscopic implosions. This sets the stage for future experiments where the implosions are seeded by intrinsic quantum or thermal fluctuations, and thus the implosions will become an experimental tool for measuring fluctuations in a BEC. |
Thursday, June 3, 2021 11:18AM - 11:30AM Live |
S06.00005: Kibble-Zurek dynamics in a trapped ultracold Bose gas I-Kang Liu, Jacek Dziarmaga, Shih-Chuan Gou, Franco Dalfovo, Nick Proukakis The study of driven phase transitions is a central question of non-equilibrium physics. Central to this is the Kibble-Zurek (KZ) scaling law, describing how fundamental observables behave close to criticality and their scaling with quench duration. Significant experimental work on this has been done in recent years, including in controlled experiments in elongated 3D harmonic traps [1], which we have previously shown to reproduce by means of stochastic numerical simulations [2]. A related question concerns whether, and under what conditions, the inhomogeneous nature of the trapping potential is consistent with predictions of the standard (homogeneous) KZ law as the system is driven across the Bose-Einstein condensation phase transition. To address this question, we analyze our simulated dynamics for the experimental conditions in the context of the linearized stochastic Gross-Pitaevskii model in the homogeneous limit. We find an exponential scaling behaviour of the momentum occupation after the transition sets in and the corresponding determined phase domain and defect number match the KZ prediction [3]. Specifically, considering the sonic horizon condition [4], we demonstrate that Ref. [1,2] fall deeply within the "homogeneous" KZ regime, with the role of inhomogeneity requiring much slower quench speeds. Our findings serve as a guide for choosing appropriate observables and parameter regimes for further experiments aimed at probing inhomogeneous effects during a driven phase transition. |
Thursday, June 3, 2021 11:30AM - 11:42AM Live |
S06.00006: Radiofrequency spectroscopy of trapped Bose polarons: crossover from the adiabatic to the diabatic regime Simeon Mistakidis, Georgios Koutentakis, Fabian Grusdt, Hossein R Sadeghpour, Peter Schmelcher The crossover of the impurity-induced spin dynamics, in trapped Bose polarons subject to radio frequency (rf) pulses of varying intensity, covering the crossover from the adiabatic to the diabatic regime is unraveled. For adiabatic pulses various polaronic excitations and mode-couplings are spectrally resolved. A temporal orthogonality catastrophe manifests in the excitation spectra, for strongly repulsive impurity-bath interactions, associated with a vanishing coherence of the impurity. Interestingly impurity-impurity correlations, for either attractive or strong repulsive couplings, are revealed inducing a spectral shift of the resonances with respect to the single impurity. Considering a heavy impurity, the polaronic peak is accompanied by a series of equidistant side-band resonances, related to interference of the impurity spin dynamics and the sound waves of the bath. By entering the diabatic transfer regime, for an increasing Rabi frequency of the applied rf field, a Lorentzian spectral shape featuring a single polaronic resonance is identified. Our findings on the effects of the external trap, rf pulse and impurity-impurity interactions provide new insights related to contemporary cold-atom experiments. |
Thursday, June 3, 2021 11:42AM - 11:54AM Live |
S06.00007: Generalized hydrodynamics in strongly interacting quenched 1D Bose gases Neel Malvania, Yicheng Zhang, Yuan Le, Jerome Dubail, Marcos Rigol, David S. Weiss The dynamics of strongly interacting quantum many-body systems are notoriously complicated and difficult to simulate. A recently developed theory called generalized hydrodynamics (GHD) promises to simplify calculations for nearly-integrable systems by following the evolution of the distribution of rapidities, which are the momenta of underlying quasiparticles. To test GHD, we initialize bundles of 1D Bose gases in both the strong and intermediate coupling strength regimes. We then perform large trap quenches and directly measure the rapidity distributions as they evolve [1]. We find excellent agreement between the evolution in these experiments and GHD theory for dimensionless coupling parameters that range from 0.3 to 9.3, demonstrating that the approximations intrinsic to GHD apply in many cold-atom experiments. We also measure the 1D momentum distributions after the quench, allowing us to infer the way in which the quasiparticles themselves evolve. |
Thursday, June 3, 2021 11:54AM - 12:06PM Live |
S06.00008: Information Scrambling in Energy-Space Lattices Saeed Pegahan, Ilya Arakelyan, John E Thomas Weakly interacting Fermi gases simulate spin lattices in energy space, offering a rich platform for investigating information spreading and spin coherence in a large many-body quantum system. We show that the collective spin vector can be determined as a function of energy from the measured spin density, enabling general energy-space resolved protocols. We measure an out-of-time-order correlation function in this system and observe the energy dependence of the many-body coherence, which is not fully substantiated by our collective spin vector model. |
Thursday, June 3, 2021 12:06PM - 12:18PM Live |
S06.00009: Quantum Phases of Time Order in Many-Body Ground States Tie-Cheng Guo, Li You Understanding phases of matter is of fundamental importance. Prior to the widespread appreciation and acceptance of topological order, the paradigm of spontaneous symmetry breaking, formulated along the Landau-Ginzburg-Wilson (LGW) dogma, is central to understanding phases and transitions between phases associated with order parameters of distinct symmetries. This work identifies ground state phases of quantum many-body system in terms of time order based on twisted vector, which is defined by us as the ground state acted on by a symmetry order parameter operator. Any nontrivial temporal structure in the two-time auto-correlation function of twisted vector implicates time order. The time order phase diagram for spin-1 atomic Bose-Einstein condensate (BEC) and quantum Rabi model are fully worked out. As a special case, the (symmetry protected) time periodic ordered phase implies the presence of continuous time crystal (CTC) and underlines the essence of CTC. We further explore the intriguing phases of time crystalline order and time functional order in non-Hermitian interaction spin models. |
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