Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session B41: Non-equilibrium Physics with Cold Atoms II |
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Sponsoring Units: DAMOP Chair: Lode Pollet, Ludwig Maximilian University Room: 350 |
Monday, March 18, 2013 11:15AM - 11:27AM |
B41.00001: Time dependent impurity in ultracold fermions: orthogonality catastrophe and beyond Michael Knap, Aditya Shashi, Yusuke Nishida, Adilet Imambekov, Dmitry A. Abanin, Eugene Demler The physics of impurities in metals and mesoscopic structures provided a deeper understanding of electrical and thermal transport properties, guided the development of new mathematical techniques, and gave useful insights into the behavior of more complicated strongly correlated materials. Ensembles of ultracold atoms offer new opportunities to study impurity physics in a well isolated, coherent setting with relatively slow time scales, that can be faithfully determined by a small number of precisely controllable parameters. In this talk, we outline a program of how to explore quantum impurity problems with ultracold atoms. In particular, we reconsider the problem of the orthogonality catastrophe (OC), which describes the dynamics of a localized impurity in a Fermi sea, and show that techniques from atomic physics, such as Ramsey pulses, spin-echo, and RF-spectroscopy, can be used to probe the OC in both time and energy domains. We present the complete solution of the OC using a combination of analytical and numerical techniques and discover new qualitative features which could not be observed in metallic systems. [Preview Abstract] |
Monday, March 18, 2013 11:27AM - 11:39AM |
B41.00002: Topological charge pumping in a one-dimensional optical lattice Lei Wang, Matthias Troyer, Xi Dai A topological charge pump transfers charge in a quantized fashion. The quantization is stable against the detailed form of the pumping protocols and external noises. Such a quantum pump shares the same topological origin as the quantum Hall effect. We propose an experiment setup to realize the topological charge pumping of cold atoms in a one-dimensional optical lattice. The quantization of the pumped charge is confirmed by first-principle simulations of the dynamics of uniform and trapped systems. Quantum effects are shown to be crucial for the topological protection of the charge quantization. Finite-temperature and non-adiabatic effect on the experimental observables are discussed. Realization of such a topological charge pump servers as a firm step towards exploring topological nontrivial phases and non-equilibrium dynamics using cold atoms. [Preview Abstract] |
Monday, March 18, 2013 11:39AM - 11:51AM |
B41.00003: Heat and spin transport in a cold atomic fermi gas Hyungwon Kim, David Huse Motivated by recent experiments measuring the spin transport in ultracold unitary atomic Fermi gases [Sommer et al., Nature (London) 472, 201 (2011); Sommer et al., New J. Phys. 13, 055009 (2011)], we explore the theory of spin and heat transport in a three-dimensional spin-polarized atomic Fermi gas. We develop estimates of spin and thermal diffusivities and discuss magnetocaloric effects, namely the the spin Seebeck and spin Peltier effects. We estimate these transport coefficients using a Boltzmann kinetic equation in the classical regime and present experimentally accessible signatures of the spin Seebeck effect. We study an exactly solvable model that illustrates the role of momentum-dependent scattering in the magnetocaloric effects. [Preview Abstract] |
Monday, March 18, 2013 11:51AM - 12:03PM |
B41.00004: Non-equilibrium steady states in quenched s-wave superfluids Maxim Dzero, Emil Yuzbashyan, Victor Gurarie Nature and microscopic structure of the non-equilibrium many-body states in strongly interacting quantum systems remains one of most active research areas in physics. In this work, we study the steady states, which appear in a s-wave superfluid at zero temperature following a quench of the pairing strength. We use the BCS Hamiltonian which we solve exactly in the thermodynamic limit using classical integrability. We obtain a generic phase diagram of the resulting steady states for quenches corresponding to an arbitrary change of the pairing strength. We calculate single particle distribution function for each of the steady states that we find. In addition, we determine the asymptotic behavior of the pairing amplitude at long times. The experimental signatures of the steady states will also be discussed. [Preview Abstract] |
Monday, March 18, 2013 12:03PM - 12:15PM |
B41.00005: Mean-field description of non-equilibrium dynamics of a 1D Bose gas in a weak optical lattice potential Juan Carrasquilla, Aaron Reinhard, Laura Zundel, Jean-Felix Riou, David Weiss, Marcos Rigol We study the expansion of a large array of one-dimensional Bose gases subject to a weak optical lattice potential using Gutzwiller mean-field calculations aimed at describing a recent experiment with ultracold atoms. We calculate the evolution of the density profile, the quasimomentum distribution, and the density profile after a band-mapping protocol followed in experiments with ultracold atoms designed to measure the quasimomentum distribution. We find that a large fraction of bosons remains trapped at the center of the lattice. Furthermore, interactions during the expansion dramatically change the momentum distribution. Our simulations qualitatively capture most aspects of the experiment. [Preview Abstract] |
Monday, March 18, 2013 12:15PM - 12:27PM |
B41.00006: Influence of the Amplitude in Lattice Modulation Spectroscopy Andreas Dirks, Karlis Mikelsons, Jim Freericks, H.R. Krishnamurthy Within the Mott-insulating phase of the Hubbard model, linear-response calculations for a periodically modulated optical lattice depth clearly predict a resonance when modulated at a frequency equal to the Hubbard repulsion U. In this work we examine the effect of the amplitude of the lattice depth modulation on the threshold for excitation. Based on a recently developed strong-coupling approach to the non-equilibrium Hubbard model, we report results on the nonlinear regime and discuss effects of the amplitude as compared to the frequency for driving excitations into the upper Hubbard band. [Preview Abstract] |
Monday, March 18, 2013 12:27PM - 12:39PM |
B41.00007: Decoherence and heating of two species fermions in optical lattices Saubhik Sarkar, Johannes Schachenmayer, Stephan Langer, Andrew J. Daley Experiments with ultracold fermionic atoms in optical lattices present a unique way to study strongly interacting many-body quantum systems, including the Fermi-Hubbard model, in a microscopically well-understood environment. A key challenge to explore many interesting quantum phases is to reach sufficiently low temperatures and therefore it is necessary to charecterise and control competing heating processes in experiments. Incoherent scattering of light from the lasers that form the lattices can contribute significantly to the heating. We study the robustness of many-body states to this mechanism, deriving a many-body master equation for two-component fermions and investigating how the heating is influenced by choices in the atomic physics and how it depends on the parameteres in the many-body Hamiltonian. [Preview Abstract] |
Monday, March 18, 2013 12:39PM - 12:51PM |
B41.00008: Diffusive Spin Transport of Lattice Fermions in One Dimension Andrew Snyder, Theja De Silva We study the long-time spin transport of fermions moving diffusively in a one dimensional lattice due to a directly introduced population imbalance and harmonic trapping potential. We combine the thermodynamic Bethe anzatz technique with the local density approximation to calculate local quantities such as magnetization and polarization. Utilizing Fick's Law, we are able to calculate the ratio of spin current to spin diffusion coefficient for both the weak and strong coupling cases that is driven by the population imbalance. We find spin current is characterized by magnetization moving from regions of low magnetization to high, with spin current being zero through insulating regions. Further, in the weak coupling limit, utilizing the linear response theory and calculating current-current correlation, we calculate local spin diffusion coefficient. The local spin diffusion coefficient shows maxima at all the insulating regions. [Preview Abstract] |
Monday, March 18, 2013 12:51PM - 1:03PM |
B41.00009: Interaction-induced transport of ultra-cold atoms in 1D optical lattices Daniel Gruss, Chih-Chun Chien, Massimiliano Di Ventra, Michael Zwolak The study of time-dependent, many-body transport phenomena is increasingly within reach of ultra-cold atom experiments. These systems not only allow experimental emulation of solid state systems, but allow us to probe the dynamics of transport at a previously unreachable level of detail. We will discuss computational results for the dynamics of electronic/atomic transport and, in particular, simulation of interacting fermionic atoms via a micro-canonical transport formalism using approximations that go beyond mean-field. We will discuss applications of this in terms of simulating particle currents under the influence of applied current and potentials, differing spin-spin interactions, and inhomogeneous lattice impurities. Finally, we will discuss these results in the context of present-day cold atom experiments.\footnote{C.C. Chien, D. Gruss, M. Di Ventra, and M. Zwolak. \\ arXiv:1203.5094v2, 2012.} [Preview Abstract] |
Monday, March 18, 2013 1:03PM - 1:15PM |
B41.00010: Effect of quantum fluctuations on classical motion near a separatrix in a weakly anharmonic lattice Rafael Hipolito, Vadim Oganesyan We investigate the role of quantum fluctuations in the relaxation of a nonequilibrium interacting system for which the phase space curve of the corresponding classical dynamics lies near a separatrix. Such a system may be realized, for example, in a weakly interacting bosonic system if we initially excite a normal mode which lies in the low quasimomentum sector for which the the system is nearly dispersionless but of nondecay type ($\omega''(q)\la 0$). As an example of such a system, we consider the case of a weakly anharmonic lattice in one dimension, where our results have some relevance to the famous Fermi-Pasta-Ulam problem. In the regime considered, we show that the classical dynamics is effectively dominated by just two normal modes which can be mapped into a single particle problem whose phase space curve lies near a separatrix. We show that for the quantum system the initial number of quanta plays the role of effective $\hbar$. Quantum fluctuations have a dramatic effect on the classical trajectory, causing the system to relax into a steady state where both the time scales associated with the relaxation and the steady state itself are strongly dependent on effective $\hbar$. [Preview Abstract] |
Monday, March 18, 2013 1:15PM - 1:27PM |
B41.00011: Emergence of long distance pair coherence through incoherent local environmental coupling Jean-Sebastien Bernier, Peter Barmettler, Dario Poletti, Corinna Kollath We demonstrate that the interplay between a purely local incoherent environmental coupling, effectively heating up the system, and Hamiltonian dynamics generates quantum coherence. For a repulsively interacting fermionic lattice gas initially prepared in a Mott insulating state, coupling a noise field to the local spin density produces coherent fermionic pairs. We show that the formation of pair coherence is approximately diffusive with distance, and is experimentally observed in the pair momentum distribution as the formation of a sharp feature at the zone boundary. [Preview Abstract] |
Monday, March 18, 2013 1:27PM - 1:39PM |
B41.00012: Dynamics of spin-1 bosons in an optical lattice Khan W. Mahmud, Eite Tiesinga We study spin-mixing and collapse and revival dynamics of spin-1 atoms in an optical lattice. Starting with the ferromagnetic or anti-ferromagnetic superfluid ground state - a sudden raising of the lattice depth creates a non-equilibrium state. Analysis of the oscillations in atom numbers in different spin states and the collapse and revivals in visibility reveals details about the system parameters and the initial superfluid state. For example, in situ number oscillations reveal the spin-dependent interactions, and visibility oscillations reveal the ratio of on-site and spin-dependent interactions, and thus the various scattering lengths in different channels can be determined. To study the interplay of superlfuidity and magnetism, we also examine the oscillations in various observables in the presence of an external magnetic field in the form of quadratic Zeeman energy. The frequency spectrum of the oscillations reveals the discrete energy levels and relative importance of different Fock states in the initial superfluid and magnetic states. [Preview Abstract] |
Monday, March 18, 2013 1:39PM - 1:51PM |
B41.00013: Fluctuation-induced dissipation in non-equilibrium moving systems Mohammad Maghrebi, Ramin Golestanian, Robert Jaffe, Mehran Kardar Quantum fluctuations in moving systems lead to nontrivial effects such as dissipation and radiation. We consider moving bodies---a single rotating object or multiple objects in relative motion---and derive the frictional force by using techniques from non-equilibrium statistical physics as well as quantum optics. The radiation to the environment is obtained as a general expression in terms of the scattering matrix which is a powerful analytical tool. We apply our general formulas to several examples of systems out of equilibrium due to their motion. [Preview Abstract] |
Monday, March 18, 2013 1:51PM - 2:03PM |
B41.00014: Dynamical Entanglement Growth and Measurement with Cold Atoms or Ions Johannes Schachenmayer, Hannes Pichler, Peter Zoller, Ben Lanyon, Andrew J. Daley Systems of cold atoms in optical lattices or a string of ions in a linear trap offer the possibility to experimentally study non-equilibrium dynamics of 1D many-body quantum systems with interactions of varying range in a controlled environment. Entanglement is a basic feature of these systems, and the increase of the entanglement entropy between different blocks of a many-body state as a function of time determines whether the long-time evolution of the system can be efficiently simulated on a classical computer. Correspondingly, states with large-scale entanglement offer regimes where quantum simulators could be used to outperform classical simulation. Thus, there is a great interest to produce large-scale entanglement in these types of experiments. Here we present analytical and numerical results on the entanglement entropy growth behavior in 1D lattice systems after a sudden quench of a model parameter, and the dependence of this growth on the range of the interactions. Furthermore, we present how bipartite R\'enyi entropies can be measured solely by using tunnel couplings and local measurements, tools which are both available in recent experiments with bosons in optical lattices. [Preview Abstract] |
Monday, March 18, 2013 2:03PM - 2:15PM |
B41.00015: Non-equilibrium scaling, response and coarsening in the quantum large N vector model Anushya Chandran, Vedika Khemani, Arun Nanduri, S. S. Gubser, S. L. Sondhi The out-of-equilibrium dynamics of a quantum system that is suddenly or slowly driven in the vicinity of critical point is conjectured to be universal and can be described in a scaling framework. The long time tails of scaling functions for a quench from the disordered to the ordered phase are of particular experimental interest. We theoretically investigate this in the $O(N)$ vector model as $N\rightarrow \infty$ for different spatial dimensions. We demonstrate that the quartic operator that is irrelevant to the equilibrium physics above the upper critical dimension is dangerously irrelevant to the long time dynamics in the scaling limit. We also observe a quantum analogue of the classical process of coarsening in which a correlation length diverges at long times in the thermodynamic limit. Suitably defined linear response measurements offer the tantalizing possibility of directly observing the non-equilibrium scaling functions; we explore these in classical models and Chern insulators as well. [Preview Abstract] |
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