Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session M01: Non-Equilibrium Physics with Cold Atoms and Molecules, Rydberg Gases, and Trapped IonsFocus
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Sponsoring Units: DAMOP DCMP Chair: Vito Scarola, Virginia Tech Room: 103 |
Wednesday, March 4, 2020 11:15AM - 11:51AM |
M01.00001: Probing quench dynamics across a quantum phase transition into a 2D Ising antiferromagnet Invited Speaker: Waseem Bakr Strongly interacting dynamics of quantum magnets is a frontier area of many body physics, and Prof Bakr's results are some of the most exciting in the area. |
Wednesday, March 4, 2020 11:51AM - 12:03PM |
M01.00002: Dynamics of a hole in a quantum antiferromagnet Annabelle Bohrdt, Fabian Grusdt, Michael Knap, Jayadev Vijayan, Pimonpan Sompet, Guillaume Salomon, Joannis Koepsell, Sarah Hirthe, Immanuel Felix Bloch, Christian Groß Understanding the properties of a single mobile hole doped into an antiferromagnet allows one to reveal the interplay of spin and charge degrees of freedom. This constitutes a crucial step in the theoretical description of the Fermi-Hubbard model and by extension, strongly correlated cuprate compounds. We experimentally study the dynamical deconfinement of spin and charge excitations in real space in one dimensional Fermi-Hubbard chains of ultracold atoms. Using space- and time-resolved quantum gas microscopy, we track the evolution of the excitations through their signatures in spin and charge correlations. We numerically study the real-time dynamics of a single hole created in the ground state of the t−J model on a square lattice. Initially, the hole spreads ballistically with a velocity proportional to the hopping matrix element. At intermediate to long times, the hole propagates again ballistically but with a velocity proportional to the spin exchange coupling, showing the formation of a magnetic polaron. We provide an intuitive explanation of this dynamics in terms of a parton construction. |
Wednesday, March 4, 2020 12:03PM - 12:15PM |
M01.00003: Many-Body Dephasing after Quantum Quench with a Trapped Ion Quantum Simulator Lingzhen Guo, Harvey B Kaplan, Wen Lin Tan, Arinjoy De, Guido Pagano, Florian Marquardt, Christopher Roy Monroe We investigate many-body dephasing in the 1D transvese-filed Ising chain with long-range power-law interactions. We work in a regime where the properties of the system are closely related to the integrable Hamiltonian with global spin-spin coupling, which enables analytical predictions even for the long-time non-integrable dynamics. We study the dependence of temporal fluctuations of the average magnetization as a function of the system size. Using the eigenstate thermalization hyperthesis (ETH), we are able to give an analytical expresssion for the temopral fluctuations. We also show the first experimental observation of persistent temporal fluctuations after a quantum quench. The measured fluctuations are exponentially suppressed with increasing system size, which is consistent with our theoretical predictions. |
Wednesday, March 4, 2020 12:15PM - 12:27PM |
M01.00004: Subdiffusion and Heat Transport in a Tilted 2D Fermi-Hubbard System Elmer Guardado-Sanchez, Alan Morningstar, Benjamin M Spar, Peter T Brown, David Huse, Waseem S Bakr We study the late-time effective hydrodynamics of an isolated cold-atom Fermi-Hubbard system subject to an external linear potential (a “tilt”). We do this by observing the decay of prepared initial density waves as a function of wavelength λ and tilt strength and find that the associated decay time τ crosses over as the tilt strength is increased from characteristically diffusive to subdiffusive with τ∝λ4. In order to explain the underlying physics we develop a hydrodynamic model that exhibits this crossover. For strong tilts, the subdiffusive transport rate is set by a thermal diffusivity, which we are thus able to measure as a function of tilt in this regime. We further support our understanding by probing the local inverse temperature of the system at strong tilts, finding good agreement with our theoretical predictions. |
Wednesday, March 4, 2020 12:27PM - 12:39PM |
M01.00005: Reservoir engineering and many-body decoherence in the quantum Ising model Lincoln Carr, Daniel Jaschke, Ines de Vega We present quantitative predictions for quantum simulator experiments on Ising models from trapped ions to Rydberg chains and show how the thermalization, and thus decoherence times, can be controlled by considering common, independent, and end-cap couplings to the bath. We find (i) independent baths enable more rapid thermalization in comparison to a common one; (ii) the thermalization timescale depends strongly on the position in the Ising phase diagram; (iii) for a common bath larger system sizes show a significant slowdown in the thermalization process; and (iv) finite-size scaling indicates a subradiance effect slowing thermalization rates toward the infinite spin chain limit. We find it is necessary to treat the full multi-channel Lindblad master equation rather than the commonly used single-channel local Lindblad approximation to make accurate predictions on a classical computer. This method reduces the number of qubits one can practically classical simulate by at least a factor of 4, in turn showing a quantum advantage for such thermalization problems at a factor of 4 smaller qubit number for open quantum systems as opposed to closed ones. Thus, our results encourage open quantum system exploration in noisy intermediate-scale quantum technologies. |
Wednesday, March 4, 2020 12:39PM - 12:51PM |
M01.00006: Spin squeezing dynamics and large-spin analogues in an optical lattice clock Michael Perlin, Ana Maria Rey Spin squeezing has been studied for decades as a means to overcome the so-called standard quantum limit for measurement precision. Despite numerous poof-of-principle experiments, however, spin squeezing has yet to push the state-of-the-art in any practical sensing application. We summarize a recent proposal to generate spin squeezing dynamics of two-level Sr-87 atoms in a 3D optical lattice clock, a world-class measurement system. Our proposal combines interactions and spin-orbit coupling to generate spin-squeezed states that are robust to typical sources of experimental noise. We then discuss generalizations of our protocol to the case of multilevel fermions with SU(n)-symmetric interactions, which have been experimentally realized with nuclear spin degrees of freedom. We show how the multilevel generalization of interactions, spin-orbit coupling, and external driving fields can be treated in a simple, unified form. Finally, we discuss prospects to explore the rich dynamics of interacting multilevel systems, such as multilevel spin squeezing and SYK-like models that may feature fast scrambling behavior. |
Wednesday, March 4, 2020 12:51PM - 1:03PM |
M01.00007: Dynamic instabilities and universal relaxation in quantum spin systems Joaquin Rodriguez Nieva, Saraswat Bhattacharyya, Dries Sels, Eugene Demler The presence of symmetries and conservation laws can have striking manifestations in the dynamic behavior of interacting quantum systems. I will discuss manifestations of SU(2) symmetry on the universal dynamics of Heisenberg ferromagnets driven out of equilibrium. In particular, I will address the emergence of universal phenomena at two different timescales. Firstly, I will discuss the long-time thermalization behavior of a non-equilibrium incoherent population of magnons, and show that the distribution function can exhibit self-similar behavior in the prethermal regime[1]. Secondly, I will present a new mechanism for dynamic instabilities in a spin spiral state occuring at short timescales, and which originates from the symmetry-constrained quasiparticle interactions[2]. These two seemingly distinct phenomena provide new links between symmetries and universal phenomena occurring at different timescales. |
Wednesday, March 4, 2020 1:03PM - 1:15PM |
M01.00008: Non-local emergent hydrodynamics in a long-range quantum spin system Alexander Schuckert, Izabella Lovas, Michael Knap Generic short-range interacting quantum systems with a conserved quantity exhibit universal diffusive transport at late times. We show [1] how this universality is extended by effective classical Lévy flights in the presence of long-range couplings that decay algebraically with distance as r-α for 0.5<α≤1.5. We investigate this phenomenon in a long-range interacting XY spin chain at infinite temperature by employing non-equilibrium quantum field theory and semi classical phase-space simulations. We find that the space-time dependent spin density profiles are self-similar, with scaling functions given by the stable symmetric distributions. Hence, autocorrelations show hydrodynamic tails decaying in time as t-1/(2α-1). We also extract the associated generalized diffusion constant, and demonstrate that it follows the prediction of Lévy flights; quantum many-body effects manifest themselves in an overall time scale depending only weakly on α. Our findings can be verified with current trapped ion experiments. |
Wednesday, March 4, 2020 1:15PM - 1:27PM |
M01.00009: Nonequilibrium dynamics and transport in the frustrated two bath spin boson model Ron Belyansky, Seth P Whitsitt, Rex Lundgren, Yidan Wang, Alexey V Gorshkov The spin-boson model, describing a single two-level system coupled to an Ohmic bath of harmonic oscillators, is a paradigmatic model of open quantum systems. It has been used to understand the connection between quantum dissipation and classical friction and has been applied to a wide range of phenomena ranging from quantum impurity problems to quantum information, biological systems, and state of the art superconducting circuits experiments. In this work, we use numerical and analytical methods to study the dynamics of a generalized spin boson model where the spin is coupled to two independent Ohmic baths via non-commuting operators. It has already been shown that the two competing baths lead to peculiar effects, namely the absence of the phase transition and the coherent to incoherent crossover in the spin dynamics, both of which are well-known features of the single bath system. Here, we explicitly show how the frustration leads to reduced decoherence in the spin dynamics following a quantum quench. We also study the single-particle transport properties of a quasi 1D realization of the model and show asymmetrical features in the intra- and inter-bath elastic and inelastic scattering. |
Wednesday, March 4, 2020 1:27PM - 1:39PM |
M01.00010: Unravelling open quantum systems on a NISQ Computer Francesco Petruccione, Ilya Sinayskiy, Kyungdeock Park, June-Koo(KEVIN) RHEE It is well-know that the simulation of the stochastic Schrödinger equations unravelling the typical master equations describing the dynamics of open quantum systems is a very useful computational tool. Here, we show how such unravellings can be simulated on a NISQ computer. The quantum algorithm maintains the cost of initial state preparation constant via quantum forking. Quantum forking creates an entangled state in which a single copy of a quantum state is encoded and evolves under independent quantum processes in each subspace, thereby allowing parallel unravelling from one wave function. A protocol for implementing a generic non-Hermitian evolution using quantum circuit elements is described. The algorithm is applied to the simulation of Markovian master equations describing quantum neural networks. |
Wednesday, March 4, 2020 1:39PM - 1:51PM |
M01.00011: Linear response theory for the OTOC and entropy growth in dissipative systems. Xin Chen We formulate the linear response theory to calculate the out-of-time ordered corralator (OTOC) and the entropy growth for dissipative systems, i.e. systems suddenly coupled to a thermal bath, which helps to understand the behavior of the information scrambling in the early stage. In addition, we also discuss the linear response of the OTOC to a perturbation for systems that are constantly coupled to a thermal bath and reaches the non-equilibrium static state. Particulary, we illustrated those calculations in the Dicke model. |
Wednesday, March 4, 2020 1:51PM - 2:03PM |
M01.00012: Prethermal non-equilibrium phases in classical systems Bingtian Ye, Francisco Machado, Norman Yao High-frequency driven quantum systems exhibit long-lived prethermal regimes, where the dynamics are described by effective static Hamiltonians. The existence of such prethermal regime allows exotic non-equilibrium phases to emerge. However, generalizing these phenomena to classical many-body systems remains challenging. In our work, we elucidate the nature of the prethermal regime in classical spin systems. We first demonstrate that the chaotic nature of the classical evolution places an obstacle to define an effective prethermal Hamiltonian: for an initial state, any small error in the dynamics becomes exponentially magnified over time. While such obstacle is inevitable for a single classical trajectory, an effective description can still arise when considering the evolution of an ensemble of states. This then allows us to extend the properties of quantum prethermal dynamics to classical systems. In particular, we prove the existence of an emergent symmetry in the prethermal regime, and utilize this symmetry to generate novel non-equilibrium phases such as classical prethermal discrete time crystals (CPDTC). Finally, we will present an analytical framework as well as numerical demonstration of CPDTC. |
Wednesday, March 4, 2020 2:03PM - 2:15PM |
M01.00013: Engineering generalized Gibbs ensembles with trapped ions Florentin Reiter, Florian Lange, Shreyans Jain, Matt Grau, Jonathan P Home, Zala Lenarcic Generalized Gibbs ensembles (GGEs) have been introduced to describe stationary expectation values of local observables in integrable models with macroscopically many conservation laws. Recent advances showed that GGEs also describe more realistic nearly integrable systems which are weakly driven and open. In this case, integrability breaking perturbations determine the parameters of GGE. By tuning the coupling to the environment, it is thus possible to stabilize a broad range of tailored GGEs. |
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