Bulletin of the American Physical Society
48th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 62, Number 8
Monday–Friday, June 5–9, 2017; Sacramento, California
Session B3: Focus Session: Floquet PhysicsFocus
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Chair: Trey Porto, Joint Quantum Institute, NIST and UMD Room: 308 |
Tuesday, June 6, 2017 10:30AM - 11:00AM |
B3.00001: Rigidity, Criticality and Prethermalization of Discrete Time Crystals Invited Speaker: Norman Yao Despite being forbidden in equilibrium, spontaneous breaking of time translation symmetry can occur in periodically driven, Floquet systems with discrete time-translation symmetry. The period of the resulting discrete time crystal (DTC) is quantized to an integer multiple of the drive period, arising from a combination of collective synchronization and many body localization. In this talk, I will describe a simple model for a one dimensional discrete time crystal which explicitly reveals the rigidity of the emergent oscillations as the drive is varied. I will analyze the properties of the dynamical phase transition where the time crystal melts into a trivial Floquet insulator. Effects of long-range interactions and pre-thermalization will be considered in the context of recent DTC realizations in trapped ions and solid-state spins. [Preview Abstract] |
Tuesday, June 6, 2017 11:00AM - 11:12AM |
B3.00002: Probing the quantum limit of a chaotic system. Jackson Angonga, Eric Meier, Fangzhao An, Bryce Gadway The study of quantum chaos presents the opportunity to observe new and interesting phenomena. This work focuses on the quantum limit of a classically chaotic system. Our approach involves mapping the dynamics $^{\mathrm{87}}$Rb condensate in a (2J$+$1)-site momentum-space lattice to those of an effective non-linear spin-J model. By performing spin rotations and squeezing operations we implement the quantum kicked top, a paradigmatic model for studying chaotic dynamics. We present linear entropy measurements as a probe of the quantum-classical crossover in our kicked top lattice. We also highlight, for a squeezing Hamiltonian, the first atomic quantum gas measurements of out-of-time ordered correlators, which serve both as signatures of quantum chaos and as a measure of information scrambling in complex quantum systems. [Preview Abstract] |
Tuesday, June 6, 2017 11:12AM - 11:42AM |
B3.00003: Quantum Lyapunov Exponent of an Atomic Kicked Rotor Invited Speaker: Victor Galitski One of the most intriguing phenomena in the studies of classical chaos is the butterfly effect, which manifests itself in that small changes in initial conditions lead to drastically different trajectories. It is characterized by a Lyapunov exponent that measures divergence of the classical trajectories. The question how/if this prototypical effect of classical chaos theory generalizes to quantum systems (where the notion of a trajectory is undefined) has been of interest for decades, but became more popular recently, when it was realized that there exist intriguing connections to string theory and general relativity in some quantum chaotic models. At the center of this activity is the so-called out-of-time-ordered correlator (OTOC) - a quantity that in the classical limit seems to approximate the classical Lyapunov correlator. However, there are very few solvable models where one can actually calculate Lyapunov exponent and/or OTOC. In this talk, I will discuss the standard model of quantum and classical chaos - kicked rotor - calculate the correlator and Lypunov exponents, and show how classical chaos and Lyapunov divergence develop and cross-over to the quantum regime. We will see that the quantum out-of-time-ordered correlator exhibits a clear singularity at the Ehrenfest time, when quantum interference effects sharply kick in: transitioning from a time-independent value to its monotonous decrease with time. In conclusion, I will discuss possible experimental realizations of the model and predicted phenomena in ultracold quantum kicked rotors. [Preview Abstract] |
Tuesday, June 6, 2017 11:42AM - 11:54AM |
B3.00004: Floquet engineering of unconventional Hubbard terms and heating timescales in an interacting fermionic system Frederik Gorg, Michael Messer, Gregor Jotzu, Kilian Sandholzer, Rémi Desbuquois, Tilman Esslinger Periodically modulated systems have recently attracted much interest both from a theoretical and experimental perspective, since they can be used to create novel effective Hamiltonians which feature terms that are not accessible in static systems. In this context, we experimentally demonstrate how Floquet engineering can be used to create unconventional Hubbard terms for interacting Fermions in an optical lattice. By modulating the lattice position at a frequency close to the interaction energy of a two-body system, we can tune both the sign and magnitude of the magnetic exchange energy independently of the single particle tunneling. An open question in this context is if experimental heating timescales are favorable enough to study driven interacting many-body systems. To investigate this problem, we measure spin-spin correlations in a shaken three dimensional lattice and directly compare them to an equivalent static configuration. In addition, we perform a detailed heating study by measuring the lifetime of magnetic correlations as a function of the driving parameters. [Preview Abstract] |
Tuesday, June 6, 2017 11:54AM - 12:06PM |
B3.00005: Observation of discrete time-crystalline order in a disordered dipolar many-body system Soonwon Choi, Joonhee Choi, Renate Landig, Georg Kucsko, Hengyun Zhou, Junichi Isoya, Fedor Jelezko, Shinobu Onoda, Hitoshi Sumiya, Vedika Khemani, Curt von Keyserlingk, Norman Yao, Eugene Demler, Mikhail Lukin The interplay of periodic driving, disorder, and strong interactions has recently been predicted to result in exotic ``time crystalline’’ phases, which spontaneously break the discrete time translation symmetry of the underlying drive. Here, we report the experimental observation of such discrete time crystalline order in a driven, disordered ensemble of dipolar spin impurities in diamond at room temperature. We observe long lived temporal correlations at integer multiples of the fundamental driving period, experimentally identify the phase boundary and find that the temporal order is protected by strong interactions; this order is remarkably stable against perturbations, even in the presence of slow thermalization. We provide a theoretical description of approximate Floquet eigenstates of the system based on product state ansatz and predict the phase boundary, which is in qualitative agreement with our observations. Our work opens the door to exploring dynamical phases of matter and controlling interacting, disordered many body systems. [Preview Abstract] |
Tuesday, June 6, 2017 12:06PM - 12:18PM |
B3.00006: Emergent Floquet states in strongly-driven optical lattices Zachary Geiger, Kurt Fujiwara, Kevin Singh, Ruwan Senaratne, Shankari Rajagopal, Mikhail Lipatov, David Weld We report on progress towards experimental observation of an emergent state of matter using ultracold lithium in an amplitude-modulated optical lattice. In the presence of very strong (sign-changing) modulation in a specific frequency range, a dynamically stable state emerges which can be understood as a direct quantum-mechanical analogue of the classical Kapitza pendulum. Realization of such a state provides an experimental context in which the effects of tunneling and tunable interactions on Floquet phases of matter can be controllably explored. [Preview Abstract] |
Tuesday, June 6, 2017 12:18PM - 12:30PM |
B3.00007: Mott Time Crystal: Models and Realizations in Cold Atoms Biao Huang, Ying-Hai Wu, W Vincent Liu Time crystals, a phase showing spontaneously breaking of time-translation symmetry, has been an intriguing subject for systems far away from equilibrium. Recent experiments found such a phase both in the presence and absence of localization, while in theories localization is usually assumed a priori. In this work, we point out that time crystals can generally exist in systems without disorder and is not in a pre-thermal state. A series of driven interacting ladder models are proposed to demonstrate this unexpected result in principle. Robust time crystalline orders are found in the Mott regime due to the emergent integrals of motion in the dynamical system, which can be characterized by the out-of-time-order correlators (OTOC). We propose two cold atom experimental schemes to realize the Mott time crystals, one by making use of dipolar gases and another by synthetic dimensions. [Preview Abstract] |
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