Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session H24: NonEquilibrium Physics in AMO Systems IIFocus

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Sponsoring Units: DAMOP DCMP Chair: Johannes Motruk, Lawrence Berkeley National Laboratory Room: BCEC 159 
Tuesday, March 5, 2019 2:30PM  2:42PM 
H24.00001: Phonon excitations in a one dimensional Bose gas Federica Cataldini, Bernhard Rauer, Thomas Schweigler, SiCong Ji, Mohammadamin Tajik, Joao Sabino, Joerg Schmiedmayer Cold atomic gases provide a powerful tool to investigate quantum manybody systems [1]. Phonons, which are lowenergy collective excitations for one dimensional superfluids, play a major role in the relaxation dynamics of such systems. It has been shown that mechanisms of phonon dephasing and rephasing generate, respectively, losses and recurrences of coherence in a quantum isolated system, and that the long time behavior of the system itself is determined by the spectrum of the phononic modes [2]. In our experiment we are able to excite and detect phonon modes individually and to monitor them over time. 
Tuesday, March 5, 2019 2:42PM  2:54PM 
H24.00002: Exact strongETH violating eigenstates and quasiparticle descriptions of manybody scar states in the Rydbergblockaded atom chain ChengJu Lin, Olexei I Motrunich A recent experiment in the Rydberg atom chain observed unusual oscillatory quench dynamics with a period2 charge density wave initial state (Z2 state), and theoretical works identified a set of manybody ``scar states'' in the Hamiltonian as potentially responsible for the atypical dynamics. In the same nonintegrable Hamiltonian, we discover several eigenstates at infinite temperature that can be represented exactly as matrix product states with finite bond dimension, for both periodic boundary conditions (two exact E = 0 states) and open boundary conditions (two E = 0 states and one each E = ± √2). This discovery explicitly demonstrates violation of strong eigenstate thermalization hypothesis in this model. These states show signatures of translational symmetry breaking with period2 bondcentered pattern, despite being in 1d at infinite temperature. We show that the whole tower of Z2 manybody scar states can be excellently approximated as single or multiple ``quasiparticle excitations" on top of our exact E = 0 states, and propose a quasiparticle explanation of the strong oscillations observed in experiments. We also discuss the possibility of similar construction for Z3 manybody scar states relevant for quench with period3 CDW initial state. 
Tuesday, March 5, 2019 2:54PM  3:06PM 
H24.00003: Observation of NonGaussian Statistics and Levy Flights in Nitrogen Vacancy Centers David Levonian, Michael L Goldman, Kristiaan De Greve, Susanne F Yelin, Mikhail Lukin A nitrogenvacancy center can be used as a probe of the interacting 
Tuesday, March 5, 2019 3:06PM  3:18PM 
H24.00004: Detection of quantum phases via outoftimeorder correlators Ceren Dag, Kai Sun, Luming Duan We elucidate the relation between outoftimeorder correlators (OTOCs) and phase transitions via analytically studying the OTOC dynamics both in nondegenerate and degenerate spectra. Our method indicates that for a wide variety of quantum phase transitions, OTOCs can directly characterize various quantum phases as well as their symmetry breaking patterns. Key ingredients about how to utilize OTOC to detect and characterize a quantum phase transition are presented. We further discuss how our method could be useful to understand the dynamical features of the OTOCs. 
Tuesday, March 5, 2019 3:18PM  3:30PM 
H24.00005: Beyond Bose Fireworks: Stimulated Emission of Exotic Shaken Condensates Han Fu, Jooheon Yoo, Lei Feng, Cheng Chin, Kathryn Levin Periodic modulation of the twobody interaction in a Bose condensate has led to the interesting observation of “Bose fireworks” [Nature 551, 356–359 (2017)]; these were later shown to be well captured by our timedependent GrossPitaevskii simulations [arXiv:1807.08781]. The promise of these experiments is that this stimulated emission may, through the process of parametric amplification, make it possible to unravel the structure (i.e., wavefunction amplitude and phase) of an unknown condensate. We seek to fulfill this promise by presenting numerical simulations of analogous fireworks patterns in more complex systems. We consider single and multiple imprinted vortices (giving rise to "chiral jets") as well as more exotic states. Using the farfield jets to reveal the character of the initial condensate is reminiscent of established procedures in particle physics and we address how this expertise can be exploited. 
Tuesday, March 5, 2019 3:30PM  3:42PM 
H24.00006: Dynamical critical behavior of longrange spin models Paraj Titum, Mohammad Maghrebi Long range interacting spin models exhibit a variety of ordertodisorder phase transitions. We consider prototypical longrange spins models, and investigate dynamical properties of the order parameter as well as entanglement after a sudden quench in the Hamiltonian. The quench dynamics is studied through a combination of exact numerics and analytical calculations. We show that, depending on the nature of quench, different dynamical critical behavior arises. Specifically, we identify regimes when the stationary state at long times exhibits a nonthermal scaling behavior, and describe the signatures in the entanglement. Our results are amenable to realization in experiments with trappedion experiments where longrange interactions naturally arise. 
Tuesday, March 5, 2019 3:42PM  3:54PM 
H24.00007: Floquet resonances from integrability: Spin polarization in a driven central spin model Pieter W. Claeys, Stijn De Baerdemacker, JeanS�bastien Caux Adiabatically varying the driving frequency of a periodically driven manybody quantum system can induce controlled transitions between resonant eigenstates of the timeaveraged Hamiltonian, corresponding to adiabatic transitions in the Floquet spectrum and presenting a general tool in quantum manybody control. Using the central spin model as an application, we show how such controlled driving processes can lead to a polarizationbased decoupling of the central spin from its decoherenceinducing environment at resonance. While it is generally impossible to obtain the exact Floquet Hamiltonian in driven interacting systems, we exploit the integrability of the central spin model to show how techniques from quantum quenches can be used to explicitly construct the Floquet Hamiltonian in a restricted manybody basis and model Floquet resonances. 
Tuesday, March 5, 2019 3:54PM  4:06PM 
H24.00008: FloquetInduced Superfluidity with Periodically Modulated Interactions of TwoSpecies Hardcore Bosons in a Onedimensional Optical Lattice Shijie Hu, Tao Wang, Sebastian Eggert, Axel Pelster, Xuefeng Zhang We consider two species of hardcore bosons in a onedimensional optical lattice with periodically modulated repulsive interactions. Using Floquet theory the periodic can be mapped to an effective Hamiltonian for high frequencies, which is described by a static interaction and hopping parameters that depend on the local densities. In particular, if the density difference of one species is nonzero on neighboring sites, the effective hopping of the other species is reduced and can even take on negative values. Using a combination of analytic calculations and different numerical simulations we establish the full quantum phase diagram for halfinteger filling for this system. The densitydependent reduction of hopping drives a quantum phase transition into a superfluid phase. For negative hopping a previously unknown state is found, where one species induces a gauge phase of the other species, which leads to a new superfluid phase. The corresponding experimental signatures in timeofflight experiments are calculated and show characteristic signatures of the different phases. 
Tuesday, March 5, 2019 4:06PM  4:18PM 
H24.00009: Analysis of weaklydriven multiemitter cQED systems Rahul Trivedi, Marina Radulaski, Kevin A Fischer, Jelena Vuckovic, Shanhui Fan In this work, we show that a weakly driven multiemitter cQED system can be analyzed by approximating the driving coherent state with a single and twophoton Fock state, and using the Scattering matrix formalism to analyze the response of this system to these Fock states. This is a significantly more computationally feasible approach than the master equation formalism, allowing the analysis of multiemitter systems with ~50 emitters. We use this approach to analyze the transmission and second order correlations induced in the incident coherent state by the multiemitter system. In particular, we show that for identical emitters, increasing the number of emitters does not improve the polaritonic photon blockade. Moreover, we analyze the impact of inhomogeneous broadening on the second order correlation function of the light emitted by the multiemitter system with large number of emitters, and analyze the emergence and behaviour of subradiant photon blockade in such multiemitter systems. 
Tuesday, March 5, 2019 4:18PM  4:30PM 
H24.00010: The Density Matrix Renormalization Group for Periodically Driven ManyBody Systems Shaon Sahoo, Imke Schneider, Sebastian Eggert Driving a quantum system periodically in time can profoundly alter its longtime dynamics and trigger exotic quantum states of matter. We propose a new DMRG method which directly deals with the Fourier components of the eigenstates of a periodically driven system using Floquet theory. With this new method we can go beyond effective Hamiltonians and take into account higher Floquet modes. Numerical results are presented for the isotropic Heisenberg antiferromagnetic spin1/2 chain under both local (edge) and global driving for energies, spinspin correlation and temporal fluctuations. As the frequency is lowered, the spin system enters into a Floquet regime with a coherent exciations of a large number of Floquet modes, which shows characteristic quantum correlations that cannot be described by any effective static model. 
Tuesday, March 5, 2019 4:30PM  4:42PM 
H24.00011: Effective Cross Section Enhancement from Embedded Atomic Lattice Impurities Taylor Patti, Dominik S Wild, Ephraim Shahmoon, Mikhail Lukin, Susanne F Yelin Atoms arranged in a twodimensional lattice strongly interact with light via collective excitations. Such lattices can be supplemented with impurity atoms which couple to the collective array modes and permit the manipulation of emission properties. In particular, the combination of strong arraylight coupling and large impurity atom nonlinearity enable highly nonlinear responses to collminated, farfield radiation. We explore the effective enhancement of impurity cross section which results from this coupling in a variety of lattice potentials and parameter regimes. Higherorder photon correlations are calculated and pertinet extensions, such as longlived photon bound states and multiimpurity systems, are discussed. 
Tuesday, March 5, 2019 4:42PM  4:54PM 
H24.00012: Scrambling dynamics across a thermalizationlocalization quantum phase transition Subhayan Sahu, Shenglong Xu, Brian Swingle We study quantum information scrambling, specifically the growth of Heisenberg operators, in large disordered spin chains using matrix product operator dynamics to scan across the thermalizationlocalization quantum phase transition. We observe ballistic operator growth for weak disorder, and a sharp transition to a phase with subballistic operator spreading. The critical disorder strength for the ballistic to subballistic transition is well below the many body localization phase transition, as determined from finite size scaling of energy eigenstate entanglement entropy in small chains. In contrast, at the eigenstate localization transition, the operator dynamics changes from a powerlaw behaviour to logarithmic, which is hard to detect from our numerics. These data are discussed in the context of a universal form for the growing operator shape and substantiated with a simple phenomenological model of rare regions. 
Tuesday, March 5, 2019 4:54PM  5:06PM 
H24.00013: Quantum Brownian motion in a quasiperiodic potential Aaron Friedman, Romain Vasseur, Austen Lamacraft, Siddharth A Parameswaran We study the behavior of a quantum particle in one dimension subject to Ohmic dissipation, moving in a bichromatic quasiperiodic potential. The bath is described by the CaldeiraLeggett model; absent the potentials, the particlebath system resolves the Langevin equation in the classical limit. In a singleperiod potential, the particle undergoes a zerotemperature localizationdelocalization transition as dissipation strength is decreased. We show that the delocalized phase is absent in the quasiperiodic case, even when the deviation from periodicity is infinitesimal. Using the renormalization group, we determine how the crossover time to the localized phase depends on the dissipation strength and incommensurability of the two frequencies, and from this, extract a localization length. Finally, we show that a similar problem can be realized as the strongcoupling limit of a mobile impurity moving in a periodic optical lattice and immersed in a onedimensional Fermi or Bose gas. 

H24.00014: ABSTRACT WITHDRAWN

Tuesday, March 5, 2019 5:18PM  5:30PM 
H24.00015: Memories of Initial States in the Dynamics of Disordered Systems Ahana Chakraborty, Pranay Gorantla, Rajdeep Sensarma We consider the dynamics of a one dimensional closed disordered system of noninteracting bosons/fermions which is initialized to a Fock state with a pattern of 0 and 1 particles on alternating sites. We show that in the long time limit, the imbalance between the densities in the two sublattices reach a finite value in the localized phase given by, I(∞) = Tanh ( 1/ 2 ξ), where ξ is the localization length. For a chain with random potential disorder, the imbalance is finite for any disorder, whereas for the Aubrey Andre model, it shows a localizationdelocalization transition. For a modified Aubrey Andre model, the imbalance as a function of the disorder shows a kink when the mobility edge first appears. We find that in this case, I(∞) = ∑_{i} Tanh [ 1/ 2 ξ^{i}], where ξ^{i }is the localization length corresponding to each of the three bands in the model. Our work relates experimentally measureable nonequilibrium quantities in these systems to the localization length and hence shows a new method for extracting the localization length in these systems. 
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