Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session L01: Long-Ranged Interactions and Nonequilibrium SystemsPrize/Award
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Sponsoring Units: DAMOP Chair: Mikael Rechtsman, Pennsylvania State University Room: 103 |
Wednesday, March 4, 2020 8:00AM - 8:36AM |
L01.00001: George E. Valley Jr. Prize Talk: Prethermal phases of matter in long-range interacting and classical many-body systems Invited Speaker: Norman Yao Recent advances suggest that physical systems, which are taken out of equilibrium, can exhibit phenomena fundamentally richer than their static counterparts. For example, certain phases of matter that are provably forbidden in equilibrium, such as discrete time crystals, have found new life in periodically driven, non-equilibrium systems. In this talk, I will define the essential features of time crystalline order and describe two new venues where such order can be observed: 1) in a 1D disorder-free, long-range interacting system and 2) in a classical spin system. In both cases, the underlying workhorse is Floquet prethermalization - a phenomena which occurs in the high frequency limit of periodically driven many-body systems; in particular, when the drive frequency is large compared with the local energy scales of the system, there can exist a long-lived quasi-steady state - a so-called "prethermal" state - in which ordered phases of matter can remain stable for exponentially long time scales. |
Wednesday, March 4, 2020 8:36AM - 8:48AM |
L01.00002: Spin squeezing in the XXZ model with power-law interactions Chunlei Qu, Ana M. Rey Spin squeezed states are known to be a useful resource for quantum metrology. Although there have been many proposals on how to generate spin squeezing, most of the dynamical generations involve collective Ising interactions via the so-called one axis twisting (OAT) model. In this talk, we will present our recent results on spin squeezing generation in the XXZ model with power-law interactions. Despite the inhomogeneous character of the spin couplings, we find this system can exhibit a level of spin-squeezing similar to that generated by the OAT model. We will report on our systematic investigation of this model and explain the mechanism responsible for the large spin squeezing generation. Our results are useful for state-of-the-art ultracold polar molecular experiments where pinned molecules in an optical lattice can interact with each other by long-range dipolar interactions and for trapped ion crystals featuring long-range interactions mediated by the phonon modes of the crystal. |
Wednesday, March 4, 2020 8:48AM - 9:00AM |
L01.00003: Persistence of power-law correlations in nonequilibrium steady states of gapped quantum spin chains Jarrett Lancaster, Joseph P Godoy The existence of quasi-long range order is demonstrated in nonequilibrium steady states in isotropic XY spin chains including of two types of additional terms that generate a gap in the energy spectrum. The system is driven out of equilibrium by initializing a domain-wall magnetization profile through application of external magnetic field and switching off the magnetic field at the same time the energy gap is activated. An energy gap is produced by either applying a staggered magnetic field in the transverse direction or introducing a modulation to the XY coupling. The magnetization, spin current and spin-spin correlation functions are computed in the thermodynamic limit at long times after the quench. For both types of systems, we find the persistence of power-law correlations despite the ground state correlation functions exhibiting exponential decay. It is discussed how these power-law correlations appear related to the periodic nature of the perturbation which generates the energy gap. |
Wednesday, March 4, 2020 9:00AM - 9:12AM |
L01.00004: Locality and Heating in Periodically Driven, Power-law Interacting Systems Minh Cong Tran, Adam Ehrenberg, Andrew Guo, Paraj Titum, Dmitry Abanin, Alexey V Gorshkov Periodically driven quantum systems with local interactions take exponentially long to heat up. We study the heating time in periodically driven D-dimensional systems with interaction strengths that decay with the distance r as a power-law 1/rα. Using a theory based on linear response, we show that the heating time is exponentially long as a function of the drive frequency for α > D. For systems that may not obey linear response theory, we use a more general Magnus-like expansion to show the existence of quasi-conserved observables, which implies exponentially long heating time for α > 2D. We also generalize recent state-of-the-art Lieb-Robinson bounds for power-law systems from two-body to k-body interactions and thereby obtain a longer heating time than previously established in the literature. Additionally, we conjecture that the gap between the bounds from the linear response theory and the Magnus-like expansion does not stem from physical differences in the theories, but rather from the lack of tight Lieb-Robinson bounds for power-law interactions. We show that the gap vanishes in the presence of a hypothetical, tight bound, and report on recent steps toward achieving this ideal bound for one-dimensional systems. |
Wednesday, March 4, 2020 9:12AM - 9:24AM |
L01.00005: Origin of the slow growth of entanglement entropy in long-range interacting spin systems Silvia Pappalardi, Alessio Lerose Long-range interactions allow far-distance quantum correlations to build up very fast. Nevertheless, numerical simulations demonstrated a dramatic slowdown of entanglement entropy growth after a sudden quench. In this work, we unveil the general mechanism underlying this counterintuitive phenomenon for generic d-dimensional quantum spin systems with slowly-decaying interactions. We demonstrate that the semiclassical rate of collective spin squeezing governs the dynamics of entanglement, leading to a universal logarithmic growth in the absence of semiclassical chaos. In fact, the standard quasiparticle contribution is shown to get suppressed as the interaction range is sufficiently increased. All our analytical results agree with numerical computations for quantum Ising chains with long-range couplings. Our findings thus identify a qualitative change in the entanglement production induced by long-range interactions and are experimentally relevant for accessing entanglement in highly-controllable platforms, including trapped ions, atomic condensates, and cavity-QED systems. |
Wednesday, March 4, 2020 9:24AM - 9:36AM |
L01.00006: Orthogonality catastrophe with long-range interactions Wei Xia, Xiaopeng Li Anderson orthogonality catastrophe is a fundamental property of fermions with a fermi surface subjected to a scattering potential. The case of finite-range potential has been well-understood. Recently, long-range interaction has been achieved in numerous quantum systems such as trapped ions, Rydberg atoms, and polar atoms/molecules. In this talk, I will present our recent study on Anderson orthogonality catastrophe with long rang interaction in one, two, and three dimensions. With a power-law type long-range interaction 1/r^α, we find in one dimension that there is critical α below which the conventional AOC scenario does not hold. In both two and three dimensions, we establish that the AOC holds generically for any value of α This can be attributed to the energy barrier produced by angular motion in two and three dimensions, which is absent in one dimension. We show our theoretical results can be readily tested in trapped ions and tweezer-array confined Rydberg atoms. |
Wednesday, March 4, 2020 9:36AM - 9:48AM |
L01.00007: Measurement-Induced Phase Transitions in Long-range Quantum Circuits Maxwell Block, Yimu Bao, Soonwon Choi, Ehud Altman, Norman Yao Hybrid quantum circuits, in which random unitary gates are interspersed with projective measurements, can exhibit a phase transition between volume- and area-law scaling of steady-state entanglement entropy, owing to the competition between information scrambling and measurements. Long-range interactions can scramble information parametrically faster than short-range interactions, suggesting they may qualitatively modify the transition. In this talk, we study 1D long-range hybrid quantum circuits where each unitary is a random two-qubit Clifford gate with range sampled from a 1/r^α power law distribution. We find that the presence of long-range interactions changes the universality of the transition: for α>3, the critical exponents agree with studies of nearest-neighbor hybrid circuits, while for α<3 the critical exponents change continuously with α. In particular, we find the dynamical exponent z<1 for α<3, indicating the transition cannot be described by conformal field theory. Moreover, for α<2 the area-law scaling crosses over to a sub-volume law scaling in which entanglement entropy grows with system size, even under high measurement rates. Our work is especially relevant for hybrid quantum circuits realized in experimental systems with inherently long-range interactions. |
Wednesday, March 4, 2020 9:48AM - 10:00AM |
L01.00008: Quantum Simulation and Computation with Programmable Rydberg Atom Arrays Alexander Keesling, Harry Levine, Ahmed Omran, Giulia Semeghini, Sepehr Ebadi, Dolev Bluvstein, Hannes Pichler, Markus Greiner, Vladan Vuletic, Mikhail Lukin Arrays of neutral atoms in reconfigurable geometries has arisen as a powerful platform for quantum science in the past few years. Strong and controllable interactions introduced through the Rydberg blockade mechanism lead to a rich set of both equilibrium and non-equilibrium many-body phenomena. Recently we have used a one-dimensional version of this platform to study the critical properties of various quantum phase transitions, generate large N-partite entangled states, and develop new techniques to implement two- and three-qubit quantum logic gates with high fidelity. |
Wednesday, March 4, 2020 10:00AM - 10:12AM |
L01.00009: Observation of nanoscale hydrodynamics in a strongly interacting dipolar spin ensemble in diamond --- Theory Francisco Machado, Chong Zu, Bingtian Ye, Bryce H Kobrin, Thomas Mittiga, Satcher Hsieh, Prabudhya Bhattacharyya, Tim O Hoehn, Soonwon Choi, Christopher Laumann, Dmitry Budker, Norman Yao Establishing a quantitative connection between the microscopic description of a quantum many-body system and its emergent macroscopic phenomena remains an important open problem. In this talk, we introduce a novel method that combines analytical, numerical, and experimental approaches to address this challenge. Strongly motivated by recent experiments that utilize strongly interacting dipolar spin ensembles in diamond, we present a framework to efficiently describe the spin dynamics. More specifically, starting from a microscopic Hamiltonian description of the spin ensemble, we construct an effective classical description of the spin polarization dynamics that accurately captures the experimental observations. Our method highlights a hybrid approach to study emergent hydrodynamics in strongly interacting quantum systems. |
Wednesday, March 4, 2020 10:12AM - 10:24AM |
L01.00010: Observation of nanoscale hydrodynamics in a strongly interacting dipolar spin ensemble in diamond --- Experiment Chong Zu, Francisco Machado, Bingtian Ye, Bryce H Kobrin, Thomas Mittiga, Satcher Hsieh, Prabudhya Bhattacharyya, Tim O Hoehn, Soonwon Choi, Christopher Laumann, Dmitry Budker, Norman Yao Bridging the gap between microscopic quantum dynamics and macroscopic emergent phenomena is an important open problem in quantum many-body physics. In this talk, we introduce a novel platform, based upon nitrogen-vacancy (NV) color centers surrounded by a dense ensemble of substitutional nitrogen (P1) centers in diamond, to experimentally probe nanoscale spin diffusion. In this platform, the NV centers serve as both entropy sinks for initializing the P1 ensemble and time-resolved probes of local spin dynamics. Using a combination of static and driven fields, we are able to independently control different parameters such as the strength of interaction and disorder, allowing us to probe the quench dynamics of the strongly interacting spin ensemble under various conditions. We find that the late time dynamics of the P1 ensemble agrees with an effective description based on emergent hydrodynamics, from which we estimate diffusion coefficients. |
Wednesday, March 4, 2020 10:24AM - 10:36AM |
L01.00011: A reconfigurable blue-detuned lattice for neutral atom quantum computing Brandon Grinkemeyer, Trent Graham, Minho Kwon, Zachary A Marra, Xiaoyu Jiang, Martin Lichtman, Matthew F Ebert, Mark Saffman We present a novel approach to forming a blue-detuned optical lattice for single Cesium atoms. This approach makes use of Acousto-Optic Deflectors (AOD) in conjunction with diffractive elements to form a lattice of crossed lines. Due to the frequency shifts introduced by the AOD we eliminate Talbot planes that have posed problems for previous blue-detuned trapping schemes. By using AODs we also gain control over the size and spacing of the traps. The tunability of the size of the trap offers a parameter that can be used to find a magic trapping condition for the ground and Rydberg states of the atom. Additionally, the ability to reconfigure spacing allows us to tune Rydberg interaction strengths. The combination of these degrees of freedom makes this trap ideal for studying quantum computation and simulation with neutral Rydberg atoms. |
Wednesday, March 4, 2020 10:36AM - 10:48AM |
L01.00012: The Measurement-Driven Entanglement Phase Transition: Relation to Cluster Fragmentation Sagar Vijay We study the dynamics of a collection of spins evolving under unitary gates and random projective measurements, and in the absence of spatial locality. For a certain choice of Clifford unitary gates, we map the wavefunction of the spins to the state of an evolving cluster, which undergoes a dynamical "fragmentation" transition as a function of the measurement rate. This classical dynamical transition corresponds to a phase transition in the asymptotic state of the spins; above a critical rate of applied measurements, the system exists in a product state over extensively many subsystems, while below this threshold, the wavefunction is no longer separable, and all subsystems develop volume-law entanglement. We show that the scaling of the entanglement entropy, which is related to the connectivity of the evolving cluster, distinguishes between the two phases, and identify a protocol to measure a local order parameter for this transition. The dynamics of the cluster may be studied analytically to determine other properties of the state of the spins, such as the distribution of stabilizer lengths. We discuss the relevance of our results to the measurement-driven entanglement transition that has been observed in higher dimensions. |
Wednesday, March 4, 2020 10:48AM - 11:00AM |
L01.00013: Measurement-Induced Phase Transitions in Many-Body Localized and Integrable Systems Yimu Bao, Soonwon Choi, Ehud Altman Recent works have shown the competition between scrambling unitary dynamics and local projective measurements can lead to a phase transition in the dynamics of entanglement entropy. In integrable systems, the extensive number of conserved quantities strongly constrains the information scrambling. Here, we show that such systems can still exhibit an entanglement phase transition given an appropriate choice of measurement basis. We analyze a toy model of many-body localized systems as a paradigmatic example. If the observables being measured are not scrambled in unitary evolution, the growth of entanglement is prohibited by any finite rate of measurements. In contrast, if measured observables are scrambled, the unitary evolution can hide and protect quantum correlations from measurements, leading to a phase transition at a nonvanishing measurement rate. The phase transition in other integrable systems, such as free fermionic and Bethe-ansatz solvable systems are also explored. Our results further corroborate the understanding of the phase transition in terms of quantum error correcting properties of the scrambling dynamics. |
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