Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session L27: Driven and Dissipative AMO Systems 
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Sponsoring Units: DAMOP DQI Chair: Fernando Sols, Universidad Complutense de Madrid Room: LACC 404B 
Wednesday, March 7, 2018 11:15AM  11:27AM 
L27.00001: ColdAtom Quantum Simulation of Ultrafast Dynamics Ruwan Senaratne, Shankari Rajagopal, Toshihiko Shimasaki, Peter Dotti, David Weld We demonstrate a quantum simulator of ultrafast phenomena, in which timevarying forces on neutral strontium atoms in a tunable optical trap emulate the electric fields of a pulsed laser acting on electrons or nuclei in a binding potential. The simulator operates in regimes equivalent to those of ultrafast and strongfield pulsedlaser experiments, opening up an unexplored application of quantum simulation techniques and a complementary path towards investigating open questions in ultrafast science. The wide difference in energy scales between simulator and simuland gives rise to a temporal magnification factor of up to twelve orders of magnitude, simplifying experimental access to the dynamics. The correspondence with ultrafast science is demonstrated by a sequence of experiments: we perform nonlinear spectroscopy of a manybody bound state, control the excitation spectrum by shaping the potential, observe subcycle unbinding dynamics during a strong fewcycle pulse, and directly measure carrierenvelope phase dependence of the response to an ultrafastequivalent pulse. 
Wednesday, March 7, 2018 11:27AM  11:39AM 
L27.00002: Nonequilibrium Phases of an Incoherently Driven Strongly Correlated Photonic Lattice Alberto Biella, Florent Storme, Jose Lebreuilly, Davide Rossini, Rosario Fazio, Iacopo Carusotto, Cristiano Ciuti We explore theoretically the physics of a lattice of coupled resonators with giant optical nonlinearities where optical gain is provided by incoherently pumped twolevel systems [1]. Within a Gutzwiller meanfield approach, we predict the emergence of a dissipative phase transition associate with the spontaneous breaking of the U(1) symmetry, from a localized Mottlike phase of photons to a coherent delocalized phase, which is akin to a coherent laser of strongly correlated photons. The essence of the meanfield predictions is corroborated by finitesize simulations obtained with matrix product operators [2] and cornerspace renormalization [3] methods. An extension of the model, involving the coupling to a reservoir of populationinverted twolevel emitters with a broad distribution of transition frequencies, will be discussed [4]. 
Wednesday, March 7, 2018 11:39AM  11:51AM 
L27.00003: Hybrid model reduction techniques for semiclassical dynamics with strong quantum features Tatsuhiro Onodera, Edwin Ng, Nikolas Tezak, Hardeep Sanghera, Hideo Mabuchi While quantum models for manybody dynamical systems quickly become intractable to numerically analyze, turning to naive semiclassicalization also precludes key features such as entanglement or nonGaussianity. Often however, these features only manifest in a handful of degrees of freedom (e.g., strongly coupled atoms), while the remainder of the state remains close to some simple, lowdimensional manifold. We demonstrate a model reduction technique based on the formalism of [1], where a dynamic basis transformation using manifold coordinates can be used to reduce the complexity of the state, while retaining a full quantum description up to truncation. For concreteness, we apply this technique to a multiatom cavity QED system, where a handful of atoms strongly couple to the cavity field amidst a background of many weakly coupled atoms. We show that the manifold coordinate evolution corresponds to MaxwellBloch dynamics, while the residual quantum state features JaynesCummings physics. 
Wednesday, March 7, 2018 11:51AM  12:03PM 
L27.00004: BathInduced Interactions in a OneDimensional Dissipative Spin Chain Matthew Butcher, Jed Pixley, Andriy Nevidomskyy The spinboson model has been widely studied for its rich physics and potential for controlling entangled quantum states. In this context, we consider a onedimensional chain of quantum spins which are coupled to a common dissipative bath, which can be realized in ultracold atomic mixtures of BoseFermi gases trapped in an optical lattice. This "multiple spin boson model" has been studied for spins with effectively zero spatial separation [1], but the case of many, finitelyseparated spins has not been previously investigated due to algorithmic difficulties. When the spins are finitely separated, the bath induces longrange, frustrated spinspin interactions in both space and imaginary time. To study the effects of these induced interactions, we employ a quantumtoclassical mapping [2] to derive the action of the corresponding classical Ising model in two dimensions. We investigate the spin localization and spatial ordering in this model with classical Monte Carlo simulations, using parallel tempering and cluster update algorithms to mitigate the difficulties of dealing with a highly frustrated spin system. 
Wednesday, March 7, 2018 12:03PM  12:15PM 
L27.00005: General Linearized Theory of Quantum Fluctuations around Arbitrary Limit Cycles Carlos NavarreteBenlloch, Talitha Weiss, Stefan Walter, Germán de Valcárcel The theory of Gaussian quantum fluctuations around classical steady states in nonlinear quantumoptical systems (also known as standard linearization) is a cornerstone for the analysis of such systems. Its simplicity, together with its accuracy far from critical points or situations where the nonlinearity reaches the strong coupling regime, has turned it into a widespread technique, being the first method of choice in most works on the subject. However, such a technique finds strong practical and conceptual complications when one tries to apply it to situations in which the classical longtime solution is time dependent, a most prominent example being spontaneous limitcycle formation. Here, we introduce a linearization scheme adapted to such situations. On a conceptual level, the scheme relies on the connection between the emergence of limit cycles and the spontaneous breaking of the symmetry under temporal translations. On the practical side, the method keeps the simplicity and linear scaling with the size of the problem (number of modes) characteristic of standard linearization, making it applicable to large (manybody) systems. 
Wednesday, March 7, 2018 12:15PM  12:27PM 
L27.00006: Shortcuts to Isothermality: From Ideal to Implementable Protocols Tamiro Villazon, Dries Sels, Anushya Chandran, Anatoli Polkovnikov Fast changes in system parameters can mimic adiabatic or isothermal evolution if the system’s Hamiltonian is engineered appropriately. Constructing and implementing these Hamiltonians can be a challenging task, especially in open systems whose nonequilibrium dynamics depend on dissipative interactions with the environment. In this work, we present an ideal dissipationless protocol for a particle in a tunable harmonic potential that maintains a quasistatic isothermal state by means of a counterdiabatic driving field. We compare this benchmark to protocols which also maintain isothermality by controlling only system degrees of freedom, and provide a simple variational minimization approach to generate approximate local escorting potentials which are experimentally realizable. 
Wednesday, March 7, 2018 12:27PM  12:39PM 
L27.00007: Critical slowing down in drivendissipative BoseHubbard lattices Filippo Vicentini, Fabrizio Minganti, Riccardo Rota, Giuliano Orso, Cristiano Ciuti Dissipative phase transitions in lattice systems are currently being explored both theoretically and experimentally, but very little is known about the dynamics of such critical phenomena. After a brief introduction of the topic, we present our recent results [1] about the dynamical properties of a firstorder dissipative phase transition in coherently driven BoseHubbard systems, describing, e.g., lattices of coupled nonlinear optical cavities. Via stochastic trajectory calculations based on the truncated Wigner approximation, we investigate the dynamical behavior as a function of system size for 1D and 2D square lattices in the regime where meanfield theory predicts nonlinear bistability. We show that a critical slowing down emerges for increasing number of sites in 2D square lattices, while it is absent in 1D arrays. We characterize the peculiar properties of the collective phases in the critical region. 
Wednesday, March 7, 2018 12:39PM  12:51PM 
L27.00008: Tunnelling and Superposition in a Nonorthogonal TwoState Model Shane Kelly, Eddy Timmermans, Shanwen Tsai The twostate model has demonstrated great success in describing a variety of phenomena in Bose Einstein condensates, including Josephson oscillations, self trapping and collapse and revival. We extend this model to allow the manybody states to be constructed from nonorthogonal singleparticle orbitals. This allows us to consider more intuitive singleparticle orbitals. The use of the intuitive singleparticle orbitals uncovers hidden structure in the revivals. In addition, the possibility of using nonorthogonal orbitals to construct manybody wavefunctions allows us to numerically consider a twostate model with orbitals that adapt to their occupation number. We use this possibility to study superposition of a BEC bubble immersed in a bath condensate. 
Wednesday, March 7, 2018 12:51PM  1:03PM 
L27.00009: Wigner Function from Keldysh Field Theory Rajdeep Sensarma, Ahana Chakraborty The Wigner function is a crucial construction in the tomography of a quantum state/density matrix. Negativity of the Wigner function indicates the presence of nonclassical correlations in a system. We show a new technique to calculate Wigner functions from Keldysh field theory, which allows us to compute Wigner functions of many body density matrices. We extend the Keldysh field theory to include arbitrary initial density matrices and construct the corresponding Wigner functions. 
Wednesday, March 7, 2018 1:03PM  1:15PM 
L27.00010: Nonlocal Random Walk over Quasienergy Levels of a Driven Quantum Oscillator Mark Dykman, Yaxing Zhang, Steven Girvin The thermal distribution over the energy levels of a quantum system weakly coupled to a bath is formed as a result of the couplinginduced interlevel transitions. The transitions are thermally activated and, in a multilevel system, can be thought of as a random walk over the levels. Usually only transitions between a few neighboring levels matter. We show that a different situation occurs for periodically driven quantum oscillators. Such systems are described by Floquet (quasienergy) states. Here, the quantum noise that invariably accompanies relaxation, leads to transitions between the quasienergy levels even for T=0. We find that the stationary distribution is formed due to transitions not only between neighboring, but also between remote levels, even though the transition rates exponentially fall off with the number of intermediate levels. We study an oscillator driven close to its tripled eigenfrequency. In many respects, this is a generic example of a classically multistable driven system. It has three period3 states, and the nonlocality of the interlevel transitions determines the rate of switching between these states. Surprisingly, this switching occurs via transitions over the quasienergy barrier rather than tunneling. 
Wednesday, March 7, 2018 1:15PM  1:27PM 
L27.00011: Subsecond Coherence Against Infrared Radiation of an Atomic Cloud Trapped in a 1D Optical Lattice Superimposed on a Magic Magnetic Trap below a Persistent Supercurrent Atom Chip Tetsuya Mukai We tried to extend the coherence time of a trapped atomic cloud against D_{1}line stimulated Raman transition. As far as internal state operations of atoms are carried out for millisecond or longer, the atomic cloud must be confined in a trapping potential. The trapping potential for neutral atoms is usually constituted with an inhomogeneous magnetic or optical field, and induces energy shift, which generally causes the difference of time evolution of atomic wave function and reduces the coherence time of the trapped atomic ensemble. The coherence time of trapped atomic cloud is also limited by the other factors, e.g., atomatom collisions, environmental noise, spontaneous emission from the intermediate states, Gaussian beam profile of interacting field, and photon recoil of Raman transitions. To ameliorate these influences, we employed a 1dimensional optical lattice potential superimposed on a field insensitive (magic field) magnetic trap below a persistent supercurrent atom chip. With this setup we obtained subsecond T_{2} coherence time measured with the Ramsey interferometric technique. 
Wednesday, March 7, 2018 1:27PM  1:39PM 
L27.00012: Dipolar phase transition in the Dicke model with infinitely coordinated frustrating interaction Sergei Mukhin, Nikolay Gnezdilov We consider the Dicke Hamiltonian of a system of N half spins with infinitely coordinated antiferromagnetic interaction. This Hamiltonian arises when one considers a singlemode microwave cavity coupled to lowcapacitance Josephson junctions via the gaugeinvariant Josephson phases. We found analytically a critical coupling strength causing a first order quantum phase transition of the system into dipolar phase with symmetry breaking coherent electromagnetic field emerging in the cavity. A new analytic tool: selfconsistently ’rotating’ HolsteinPrimakoff representation for the Cartesian components of the total spin is proposed. 
Wednesday, March 7, 2018 1:39PM  1:51PM 
L27.00013: Symmetry breaking and amplification in a drivendissipative 1D cavity array Alexander McDonald, Aashish Clerk, Tami PeregBarnea We study theoretically a onedimensional array of parametrically driven photonic cavities where timereversal symmetry is broken through the parametric pump. This simple model exhibits an unusual symmetry broken phase, in which the properties of a finite chain with boundaries strongly diverge from those of an infinite system or ring. We discuss the steadystate correlation properties of this phase, as well as implications for transport and amplification. The system could be realized either using superconducting microwave circuits (see e.g. Ref. [1]), or with photonic cavities. [1] Mattias Fitzpatrick, Neereja M. Sundaresan, Andy C. Y. Li, Jens Koch, and Andrew A. Houck. Phys. Rev. X 7, 011016,(2017). 
Wednesday, March 7, 2018 1:51PM  2:03PM 
L27.00014: Interactioninduced timesymmetry breaking in driven dissipative quantum systems Christoph Bruder, Niels Lörch, Mark Dykman

Wednesday, March 7, 2018 2:03PM  2:15PM 
L27.00015: Transitionless Quantum Driving (Shortcut to Adiabaticity) via Judicious Coupling to Suitably Fluctuating External Fields Rafael Hipolito, Paul M. Goldbart For a quantum system driven by a timedependent Hamiltonian $H_0(t)$, Berry has shown that complete suppression of transitions between its instantaneous eigenstates is always possible via the addition of an auxiliary term to the Hamiltonian, $H_1(t)$, determined by $H_0(t)$. The resulting quantum evolution (driven by $H_0+H_1$), referred to as transitionless quantum driving (TQD), is then exactly adiabatic with respect to the instantaneous eigenstates of $H_0(t)$. We report an alternative way of achieving TQD, via the coupling of the quantum system to an external fluctuating field, with coupling parameter $J(t)$ and external field correlators (EFC) properly chosen. Averaging over the external field yields TQD with respect to the original quantum system. To illustrate this result, we explore the suppression of the Schwinger paircreation effect in a (1+1)D gas of Dirac fermions coupled to a timedependent electric field $E(t)$. We show that to completely suppress the Schwinger effect requires $J\propto\sqrt{E}$, and the EFCs to mimic the correlators of a 'partner' system of the original system. This partner shares properties with the SUSY partner of the Dirac fermions, suggesting a possible connection between TQD and a modified SUSY that needs to be explored further. 
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