Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session F50: Non-Equilibrium Physics with Cold AtomsFocus
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Sponsoring Units: DAMOP Chair: Joe Britton, NIST Room: Hilton Baltimore Holiday Ballroom 1 |
Tuesday, March 15, 2016 11:15AM - 11:27AM |
F50.00001: The Way to Phase Space Crystals Lingzhen Guo, Marthaler Michael, Gerd Sch\"on A novel way to create a band structure of the quasienergy spectrum for driven systems is proposed based on the discrete symmetry in phase space. The system, e.g., an ion or ultracold atom trapped in a potential, shows no spatial periodicity, but it is driven by a time-dependent field. Under rotating wave approximation, the system can produce a periodic lattice structure in phase space. The band structure in quasienergy arises as a consequence of the n-fold discrete periodicity in phase space induced by this driving field. We propose explicit models to realize such a phase space crystal and analyze its band structure in the frame of a tightbinding approximation. The phase space lattice differs fundamentally from a lattice in real space, because its coordinate system, i.e., phase space, has a noncommutative geometry. The phase space crystal opens new ways to engineer energy band structures, with the added advantage that its properties can be changed in situ by tuning the driving field’s parameters. [Preview Abstract] |
Tuesday, March 15, 2016 11:27AM - 11:39AM |
F50.00002: Floquet topological systems in the vicinity of level crossings: Reservoir induced coherence of the Floquet density matrix and steady-state entropy production Hossein Dehghani, Aditi Mitra Results are presented for a Floquet topological system for the case where the separation between quasi-energy levels becomes small, and in particular, comparable to the coupling strength to an external reservoir. For this case, even at steady-state, the reduced density matrix in the Floquet basis has non-zero off-diagonal elements, with the strength of the off-diagonal elements increasing as one approaches the level crossings. The steady-state reduced density matrix has oscillations at integer multiples of the periodic drive, and a Fourier decomposition allows the extraction of the occupation of the Floquet quasi-energy levels, which also depends on the coupling to the reservoir. The lack of detailed balance is quantified in terms of an entropy production rate. [Preview Abstract] |
Tuesday, March 15, 2016 11:39AM - 11:51AM |
F50.00003: A quantum resonance catastrophe for a periodically driven impurity Sebastian Eggert, Daniel Thuberg, Sebasti\'an Reyes There has been much interest in creating novel quantum states through active dynamic manipulations (quenches and driving) in a variety of state-of-the-art systems, such as molecular electronics, ultra-cold quantum gases, nanodot arrays, and photonic crystals. We now consider the transport in an extended one-dimensional array of coupled quantum sites which is periodically driven at one impurity location by using an exact solution with help of the Floquet theory. While a static potential barrier is known to always allow transport via tunneling, a corresponding time-periodic impurity shows resonances at special driving frequencies where the transmission is completely blocked. We find that even for an infinitesimally small periodic perturbation there is a breakdown of conductance. Such a quantum resonance catastrophe occurs when the frequency is tuned to couple to bound states just outside the band. Our results show an abundance of tuning possibilities for the transmission and the width of the resonance with frequency, potential barrier and particle energy, leading to versatile opportunities in the design of switches. [Preview Abstract] |
Tuesday, March 15, 2016 11:51AM - 12:03PM |
F50.00004: Stroboscopic Symmetry-Protected Topological Phases Luiz Santos, Thomas Iadecola, Claudio Chamon Symmetry-protected topological (SPT) phases of matter have been the focus of many recent theoretical investigations, but controlled mechanisms for engineering them have so far been elusive. In this talk, I demonstrate that by driving interacting spin systems periodically in time and tuning the available parameters, one can realize lattice models for bosonic SPT phases in the limit where the driving frequency is large. We provide concrete examples of this construction in one and two dimensions, and discuss signatures of these phases in stroboscopic measurements of local observables. Phys. Rev. B 92, 125107 (2015); arXiv:1503.07871 [Preview Abstract] |
Tuesday, March 15, 2016 12:03PM - 12:15PM |
F50.00005: Statistical Transmutation in Periodically Driven Optical Lattices Tigran Sedrakyan, Victor Galitski, Alex Kamenev We show that interacting bosons in a periodically driven two dimensional (2D) optical lattice may effectively exhibit fermionic statistics. The phenomenon is similar to the celebrated Tonks-Girardeau regime in 1D. The Floquet band of a driven lattice develops the moat shape, i.e., a minimum along a closed contour in the Brillouin zone. Such degeneracy of the kinetic energy favors fermionic quasiparticles. The statistical transmutation is achieved by the Chern-Simons flux attachment similar to the fractional quantum Hall case. We show that the velocity distribution of the released bosons is a sensitive probe of the fermionic nature of their stationary Floquet state. [Preview Abstract] |
(Author Not Attending)
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F50.00006: Driven impurity in an ultracold 1D Bose gas with intermediate interaction strength Jean-Sebastien Caux, Steve Simon, Claudio Castelnovo We study a single impurity driven by a constant force through a 1D Bose gas using a Lieb-Liniger based approach. Our calculaton is exact in the interaction amongst the particles in the Bose gas, and is perturbative in the interaction between the gas and the impurity. In contrast to previous studies of this problem, we are able to handle arbitrary interaction strength for the Bose gas. We find very good agreement with recent experiments [Phys. Rev. Lett. 103, 150601 (2009)]. [Preview Abstract] |
Tuesday, March 15, 2016 12:27PM - 12:39PM |
F50.00007: The anomalous Floquet-Anderson insulator as a non-adiabatic quantized charge pump. Paraj Titum, Erez Berg, Mark S. Rudner, Gil Refael, Netanel H. Lindner Periodically driven quantum systems provide a novel and versatile platform for realizing topological phenomena. Among these are analogs of topological insulators and superconductors, attainable in static systems; however, some of these phenomena are unique to the periodically driven case. Here, we show that disordered, periodically driven systems admit an “anomalous” two dimensional phase, whose quasi-energy spectrum consists of chiral edge modes that coexist with a fully localized bulk - an impossibility for static Hamiltonians. This unique situation serves as the basis for a new topologically-protected non-equilibrium transport phenomenon: quantized non-adiabatic charge pumping. We identify the bulk topological invariant that characterizes the new phase (which we call the “anomalous Floquet Anderson Insulator”, or AFAI). We provide explicit models which constitute a proof of principle for the existence of the new phase. Finally, we present evidence that the disorder-driven transition from the AFAI to a trivial, fully localized phase is in the same universality class as the quantum Hall plateau transition. [Preview Abstract] |
Tuesday, March 15, 2016 12:39PM - 12:51PM |
F50.00008: Exact nonadiabatic steering of quantum particles between arbitrary instantaneous eigenstates of time-dependent Hamiltonians Rafael Hipolito, Paul Goldbart We consider a system governed by a Hamiltonian $H[R_n]$ that depends on a set of parameters $R_n(t)$ that can be varied with time. We address the task of steering this system between a pair of eigenstates, one corresponding to $H[R_n(t_i)]$, the other to $H[R_n(t_f)]$. For any parameter history connecting $R_n(t_i)$ and $R_n(t_f)$, we formulate a measure of success with this task, based on a path-integral expression for the overlap between the time-evolved initial state (as driven by $H[R_n(t)]$) and the final state, which is obtained by integrating out the system degrees of freedom but which retains a dependence on the parameter history $R_n(t)$. We discuss various settings in which this program may be carried out with perfect accuracy, by optimizing the measure ofsuccess with respect to the parameter history. The task may be accomplished over timescales that are much shorter than simple adiabaticity would require and are on the order of the intrinsic timescale of the system dynamics. For illustration, we consider the example of a particle (possibly with internal freedoms) that is confined by a harmonic potential having time-varying center, curvature and squeezing parameters , for which we determine the parameter history required to steer the particle with perfect accuracy. [Preview Abstract] |
Tuesday, March 15, 2016 12:51PM - 1:03PM |
F50.00009: Geodesic paths for quantum many-body systems Michael Tomka, Tiago Souza, Steve Rosenberg, Michael Kolodrubetz, Anatoli Polkovnikov The quantum length is a distance between parameter-dependent eigenstates of an adiabatically driven quantum system. Its associated metric has many intriguing properties, for example it is related to the fidelity susceptibility, an important quantity in the study of quantum phase transitions. The metric also appears as the leading adiabatic correction of the energy fluctuations of a quantum system and gives rise to a time-energy uncertainty principle and a geometric interpretation of time. The adiabatic response of an open quantum system can as well be expressed through this metric. Further, the quantum length introduces the notion of Riemannian geometry to the manifold of eigenstates and hence allows one to define geodesics in parameter space. We study the geodesics in parameter space of certain quantum many-body systems, emerging from this quantum distance. These geodesic paths provide a well-defined optimal control protocol on how to drive the system’s parameters in time, to get from one eigenstate to another. Generating optimal evolution plays a central role in quantum information technology, adiabatic quantum computing and quantum metrology. [Preview Abstract] |
Tuesday, March 15, 2016 1:03PM - 1:15PM |
F50.00010: Hysteresis of Current in Noninteracting Atomic Fermi Gases in Optical Ring Potentials Mekena Metcalf, Chih-Chun Chien, Chen-Yen Lai Hysteresis is a ubiquitous phenomenon, which can be found in magnets, superfluids, and other many-body systems. Although interactions are present in most systems exhibiting hysteresis, here we show the current of a non-interacting Fermi gas in an optical ring potential produces hysteresis behavior when driven by a time-dependent artificial gauge field and subject to dissipation. Fermions in a ring potential threaded with flux can exhibit a persistent current when the system is in thermal equilibrium, but cold-atoms are clean and dissipation for reaching thermal equilibrium may be introduced by an external, thermal bath. We use the standard relaxation approximation to model the dynamics of cold-atoms driven periodically by an artificial gauge field. A competition of the driven time and the relaxation time leads to hysteresis of the mass current, and work done on the system, as a function of the relaxation time, exhibits similar behavior as Kramers transition rate in chemical reaction and one-dimensional thermal transport. [Preview Abstract] |
Tuesday, March 15, 2016 1:15PM - 1:27PM |
F50.00011: On Exact Solutions of Novel Multistate Landau-Zener Problems. Aniket Patra, Emil Yuzbashyan A multistate Landau-Zener (MLZ) Hamiltonian is used to model numerous non-equilibrium experiments involving cold atoms, quantum dots and quantum dot molecules. We recently showed that all the known MLZ problems either reduce to the $2 \times 2$ Landau Zener problem or belong to a family of mutually commuting Hamiltonians (that are polynomial in time).\footnote{A. Patra and E. A. Yuzbashyan, J. Phys. A: Math. Theor. {\bf 48}, 245303 (2015).} Based on this classification we identify previously unknown MLZ problems, explicitly obtain their solutions and discuss relevant experimental scenarios. [Preview Abstract] |
Tuesday, March 15, 2016 1:27PM - 1:39PM |
F50.00012: Adiabaticity in a dimerised optical lattice site with increasing laser intensity Scott Taylor, Chris Hooley Recent experiments attempting to simulate magnetic phenomena with cold atoms in optical lattices rely on systems of a few atoms in dimerised lattice sites. These atoms may be manipulated by deformations of the lattice potential, which often need to be adiabatic, but must also happen quickly. We consider such a system of two fermions in a time-dependent double well potential, described by a two-site Hubbard model with time-dependent hopping and interaction energies. The adiabaticity of the following process is analysed: the system is prepared in the ground state of a shallow potential, which is smoothly transformed to a deep potential over some period of time. Experimentally, this corresponds to ramping up the intensity of the lasers generating the lattice. We present numerical and analytical results, demonstrating principles to design fast, adiabatic ramp profiles. [Preview Abstract] |
Tuesday, March 15, 2016 1:39PM - 2:15PM |
F50.00013: Non-equilibrium dynamics of a quantum gas in a box Invited Speaker: Zoran Hadzibabic For the past two decades harmonically trapped ultracold atomic gases have been used with great success to study both equilibrium and non-equilibrium many-body physics in a flexible experimental setting. Recently, we achieved the first atomic Bose-Einstein condensate in an essentially uniform potential of an optical-box trap\footnote{A. L. Gaunt et al., Phys. Rev. Lett. {\bf 110}, 200406 (2013)}, which has opened new possibilities for closer connections with other many-body systems and the theories that rely on the translational symmetry of the system. I will present our recent experiments on non-equilibrium phenomena in this system, including the study of the Kibble-Zurek dynamics of spontaneous symmetry breaking in a quenched homogeneous gas\footnote{N. Navon et al., Science {\bf 347}, 167 (2015) }. [Preview Abstract] |
Tuesday, March 15, 2016 2:15PM - 2:27PM |
F50.00014: Spin diffusion in ultracold spin-orbit coupled $^{40}$K gas T. Yu, M. W. Wu We investigate the steady-state spin diffusion for ultracold spin-orbit coupled $^{40}$K gas by the kinetic spin Bloch equation approach. It is found that the behaviors of the steady-state spin diffusion are determined by three characteristic lengths in the system: the mean free path, the Zeeman oscillation length and the spin-orbit coupling oscillation length. It is further revealed that by tuning the scattering strength, the system can be divided into {\it five} regimes, in which the behaviors of the spacial evolution of the steady-state spin polarization shows different dependencies on the scattering strength, Zeeman field and spin-orbit coupling strength. These rich behaviors of the spin diffusions in different regimes are hard to be understood in the framework of the simple drift-diffusion model or the direct inhomogeneous broadening picture in the literature. However, almost all these rich behaviors can be well understood by means of our {\it modified} drift-diffusion model and/or {\it modified} inhomogeneous broadening picture. Specifically, several anomalous features of the spin diffusion are revealed, which are in contrast to those obtained from {\it both} the simple drift-diffusion model and the direct inhomogeneous broadening picture. [Preview Abstract] |
Tuesday, March 15, 2016 2:27PM - 2:39PM |
F50.00015: Prediction of the~expansion velocity of ultracold 1D quantum gases for integrable models Zhongtao Mei, Lev Vidmar, Fabian Heidrich-Meisner, Carlos Bolech In the theory of Bethe-ansatz integrable quantum systems, rapidities play an important role as they are used to specify many-body states. The physical interpretation of rapidities going back to Sutherland is that they are the asymptotic momenta after letting a quantum gas expand into a larger volume rendering it dilute and noninteracting. We exploit this picture to calculate the expansion velocity of a one-dimensional Fermi-Hubbard model by using the distribution of rapidities defined by the initial state [1]. Our results are consistent with the ones from time-dependent density-matrix renormalization. We show in addition that an approximate Bethe-ansatz solution works well also for the Bose-Hubbard model. Our results are of interests for future sudden-expansion experiments with ultracold quantum gases. [1] Z. Mei et al., arXiv:1509.00828 [Preview Abstract] |
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