Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session F27: Non-Equilibrium Physics with Cold Atoms and Molecules, Rydberg Gases, and Trapped Ions IFocus Live
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Sponsoring Units: DAMOP DCMP Chair: David Weld, University of California, Santa Barbara |
Tuesday, March 16, 2021 11:30AM - 11:42AM Live |
F27.00001: Eta-Pairing in Hubbard Models: From Spectrum Generating Algebras to Quantum Many-Body Scars Sanjay Moudgalya, Nicolas Regnault, Andrei Bernevig We revisit the eta-pairing states in Hubbard models and explore their connections to quantum many-body scars to discover a universal scars mechanism. Eta-pairing occurs due to an algebraic structure known as a Spectrum Generating Algebra (SGA), giving rise to equally spaced towers of eigenstates in the spectrum. We generalize the original eta-pairing construction and show that several Hubbard-like models on arbitrary graphs exhibit SGAs, including ones with disorder and spin-orbit coupling. We further define a Restricted Spectrum Generating Algebra (RSGA) and give examples of perturbations to the Hubbard-like models that preserve an equally spaced tower of the original model as eigenstates. The states of the surviving tower exhibit a sub-thermal entanglement entropy, and we analytically obtain parameter regimes for which they lie in the bulk of the spectrum, showing that they are exact quantum many-body scars. The RSGA framework also explains the equally spaced towers of eigenstates in several well-known models of quantum scars, including the AKLT model. |
Tuesday, March 16, 2021 11:42AM - 11:54AM Live |
F27.00002: From tunnels to towers: quantum scars from Lie algebras and q-deformed Lie algebras Nicholas O'Dea, Fiona Burnell, Anushya Chandran, Vedika Khemani We present a general symmetry-based framework for obtaining many-body Hamiltonians with scarred eigenstates that do not obey the eigenstate thermalization hypothesis. Our models are derived from parent Hamiltonians with a non-Abelian (or q-deformed) symmetry, whose eigenspectra are organized as degenerate multiplets that transform as irreducible representations of the symmetry ('tunnels'). We show that large classes of perturbations break the symmetry but preserve a particular low-entanglement multiplet of states -- thereby giving generic, thermal spectra with a shadow of the broken symmetry in the form of scars. Our framework applies to several known models, and we introduce new models with scars that transform as irreps of symmetries such as SU(3) and q-deformed SU(2), as well as new examples of generalized AKLT models with scar states that do not transform in an irreducible representation of the relevant symmetry. |
Tuesday, March 16, 2021 11:54AM - 12:06PM Live |
F27.00003: Field tuning to avoid the heat death of a charge-density-wave chain James Freericks, Manuel Weber Time-dependent driving of quantum systems has emerged as a powerful tool to engineer |
Tuesday, March 16, 2021 12:06PM - 12:18PM Live |
F27.00004: Theory of Resonances in Floquet Scattering Christoph Dauer, Axel Pelster, Sebastian Eggert Feshbach resonances are a common tool in order to control the scattering length in ultracold quantum gases. Using time-periodic driving one is able to induce novel resonances that are fully controllable by the parameters of the drive. In this talk we provide a deeper understanding of these driving induced resonances by introducing a theory of Floquet resonances. Our method is capable of describing resonance positions and widths for general inter-particle potentials. We show our results exemplarily in the case of a driven pseudopotential. |
Tuesday, March 16, 2021 12:18PM - 12:30PM Live |
F27.00005: Analog reheating of the early universe in the laboratory Kevin Geier, Aleksandr Chatrchyan, Markus Oberthaler, Jürgen Berges, Philipp Hauke Cosmic reheating describes the transition of the post-inflationary universe to a hot and thermal state. To shed light on the nature of this process, we propose a quantum simulation of cosmic reheating in an ultracold Bose gas. In our setup, we leverage modern experimental capabilities of modulating atomic interactions in order to account for the expansion of the universe as well as to induce parametric instabilities, mimicking the explosive particle production in the early universe. Non-linear interactions drive the system into a far-from-equilibrium state, characterized by a turbulent transport of energy towards higher moments. As we illustrate by means of classical-statistical simulations, our work opens new perspectives for an experimental study of self-similar dynamics in both universal and prescaling regimes. The proposed experiment has the potential of going beyond the weak-coupling regime of quantum field theory and access the elusive quantum-dominated relaxation to thermal equilibrium at late times. |
Tuesday, March 16, 2021 12:30PM - 12:42PM Live |
F27.00006: Adiabatic eigenstate deformations as a sensitive probe for quantum chaos Mohit Pandey, Pieter W Claeys, David Campbell, Anatoli S Polkovnikov, Dries Sels In the past decades, it was recognized that quantum chaos, which is essential for the emergence of statistical mechanics and thermodynamics, manifests itself in the effective description of the eigenstates of chaotic Hamiltonians through random matrix ensembles and the eigenstate thermalization hypothesis. Standard measures of chaos in quantum many-body systems are level statistics and the spectral form factor. In this work, we show that the norm of the adiabatic gauge potential, the generator of adiabatic deformations between eigenstates, serves as a much more sensitive measure of quantum chaos. We are able to detect transitions from non-ergodic to ergodic behavior at perturbation strengths orders of magnitude smaller than those required for standard measures. Using this alternative probe in two generic classes of spin chains, we show that the chaotic threshold decreases exponentially with system size and that one can immediately detect integrability-breaking (chaotic) perturbations by analyzing infinitesimal perturbations even at the integrable point. In some cases, small integrability-breaking is shown to lead to anomalously slow relaxation of the system, exponentially long in system size. |
Tuesday, March 16, 2021 12:42PM - 12:54PM Live |
F27.00007: Fate of quantum many-body scars in the presence of disorder Ian Mondragon, Maxim G Vavilov, Ivar Martin State-of-the-art quantum simulators have recently accessed new regimes of nonequilibrium many-body quantum dynamics. In particular, simulators based on arrays of interacting Rydberg atoms have shown unexpected non-ergodic oscillations of local observables due to the presence of quantum scars in the energy spectrum. A question, however, that has not been addressed concerns the stability of scar states against disorder. In this talk, we show, using a model of interacting disordered Rydberg atoms, that non-ergodic oscillations continue to occur near the same frequency of the clean system. This is due to the presence of multiple towers of scar resonances that remain approximately centered at the same scar energies of the clean system. We illustrate these results by calculating the magnetization and spatio-temporal correlators of the system, which we use to map out a diagram of the possible dynamical regimes. We thus show that the non-ergodic dynamics due to quantum scars is robust against disorder, which lays the groundwork for understanding experimentally realistic systems. |
Tuesday, March 16, 2021 12:54PM - 1:06PM Live |
F27.00008: Nonergodic Quantum Dynamics from Deformations of Classical Cellular Automata Thomas Iadecola, Sagar Vijay Classical reversible cellular automata (CAs), which describe the discrete-time dynamics of classical degrees of freedom in a finite state-space, can exhibit exact, nonthermal quantum eigenstates despite being classically chaotic. We show that families of periodically-driven (Floquet) quantum dynamics that include a classical CA in a special limit retain certain nonthermal eigenstates of the CA. These dynamics are nonergodic in the sense that certain product states on a periodic classical orbit fail to thermalize, while generic initial states thermalize as expected in a quantum chaotic system. We demonstrate that some signatures of these effects can be probed in quantum simulators based on Rydberg atoms in the blockade regime. These results establish classical CAs as parent models for a class of quantum chaotic systems with rare nonthermal eigenstates. |
Tuesday, March 16, 2021 1:06PM - 1:18PM Live |
F27.00009: Dissipation-induced collective excitations and nonequilibrium phase transition in fermionic superfluids Kazuki Yamamoto, Masaya Nakagawa, Naoto Tsuji, Masahito Ueda, Norio Kawakami Collective excitations in fermionic superfluids have been widely studied in condensed matter physics. In particular, recent experimental progress has enabled the studies of out-of-equilibrium dynamics of superfluid order parameters. For example, a periodic modulation of the amplitude of the order parameter excites the Higgs amplitude mode, which has been realized with ultracold atomic gases [1]. However, they inevitably suffer from atomic loss due to inelastic scattering, which has received little attention in literature. |
Tuesday, March 16, 2021 1:18PM - 1:54PM Live |
F27.00010: Optically Programmable Interactions for Cold Atoms Invited Speaker: Monika Schleier-Smith Optically controlled interactions are a powerful tool for studies of non-equilibrium physics in quantum simulators and can furthermore enable applications in quantum sensing and computation. I will report on experiments in which we use light to induce long-range spin interactions among cold atoms, and to tailor the interactions in space and time. By one approach, Rydberg dressing, we observe the mean-field dynamics of a transverse-field Ising model, including dynamical signatures of a paramagnetic-ferromagnetic phase transition. In a complementary platform, we demonstrate programmable long-range interactions in a millimeter-scale array of atomic ensembles within an optical resonator. Our scheme allows an arbitrary magnon dispersion relation to be specified via the modulation waveform of a control laser, opening the door to studies of frustrated magnetism and enabling explorations of quantum spin dynamics in exotic geometries and topologies. |
Tuesday, March 16, 2021 1:54PM - 2:06PM Live |
F27.00011: Minimal Model for Fast Scrambling Ron Belyansky, Przemyslaw Bienias, Yaroslav Kharkov, Alexey V Gorshkov, Brian Swingle We study quantum information scrambling in spin models with both long-range all-to-all and short-range interactions. We argue that a simple global, spatially homogeneous interaction together with local chaotic dynamics is sufficient to give rise to fast scrambling, which describes the spread of quantum information over the entire system in a time that is logarithmic in the system size. This is illustrated in two tractable models: (1) a random circuit with Haar random local unitaries and a global interaction and (2) a classical model of globally coupled nonlinear oscillators. We use exact numerics to provide further evidence by studying the time evolution of an out-of-time-order correlator and entanglement entropy in spin chains of intermediate sizes. Our results pave the way towards experimental investigations of fast scrambling and aspects of quantum gravity with quantum simulators. |
Tuesday, March 16, 2021 2:06PM - 2:18PM Live |
F27.00012: Correspondence principle for many-body scars in ultracold Rydberg atoms Christopher Turner, Jean-Yves Desaules, Kieran Bull, Zlatko Papic The theory of quantum scarring – a remarkable violation of quantum unique ergodicity – rests on two complementary pillars: the existence of unstable classical periodic orbits and the so-called quasimodes, i.e., the non-ergodic states that strongly overlap with a small number of the system’s eigenstates. Recently, interest in quantum scars has been revived in a many-body setting of Rydberg atom chains. While previous theoretical works have identified periodic orbits for such systems using time-dependent variational principle (TDVP), the link between periodic orbits and quasimodes has been missing. Here we provide a conceptually simple analytic construction of quasimodes for the non-integrable Rydberg atom model, and prove that they arise from a “requantisation” of previously established periodic orbits when quantum fluctuations are restored to all orders. Our results shed light on the TDVP classical system simultaneously playing the role of both the mean-field approximation and the system’s classical limit, thus allowing us to establish a rigorous link between the eigenstate scarring in the Rydberg atom chains and the single-particle quantum systems. |
Tuesday, March 16, 2021 2:18PM - 2:30PM Live |
F27.00013: Quantum phonon lasing with mixed species trapped ions Thanh Long Nguyen, Tanja Behrle, Florentin Reiter, Jonathan P Home Active control of the interaction between a quantum system and its environment, a.k.a quantum reservoir engineering (QRE) has been proved to be a rich resource for quantum state preparation and quantum computation. It also provides the possibility to study open quantum systems, in particular quantum phase transitions driven by dissipation. To explore this direction, we implement QRE on a mixed species ion crystal consisting of a calcium ion and a beryllium ion. This allows us to realize a phonon laser and study the lasing phase transition deep in the quantum regime. We also demonstrate phase locking of such a phonon laser, which can find applications in quantum sensing. The rich toolbox provided by QRE on a mixed species ion crystal enables us to further investigate a nonclassical lasing regime. Such states are of great interest for quantum-enhanced parameter estimation. |
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