Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session W33: Cold Quantum Gases |
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Sponsoring Units: DAMOP Chair: Luming Duan, University of Michigan Room: 706 |
Thursday, March 6, 2014 2:30PM - 2:42PM |
W33.00001: Dynamics of Fermionic Impurity in One Dimension Huijie Guan, Natan Andrei We study the dynamics of a fermionic impurity propagating in a one dimensional infinite line. The system is described by the Gaudin-Yang Model and is exactly solvable by the Nested Bethe Ansatz. Starting from a generic initial state, we obtain the time evolution of the wavefunction by the Yudson Approach in which we expand the initial state with the Nested Bethe Ansatz solutions. One situation that we are interested in is where, initially, the impurity is embedded in host fermions with a lattice configuration and one remove the periodic potential at time zero. We calculate the density profile and correlation functions at a later time. Another situation is to shoot an impurity into a cloud of fermions and calculate the probability for it to pass through. While the repulsive case has been studied already\footnote{C. J. Mathy and M. B. Zvonarev and E. Demler, Nature Physics \textbf{8}, 881(2012)}, we extend it to the attractive case and study the role of bound states in the evolution. We are also interested in boson impurity problem, where not only impurity interacts with host particles, all host particles interact with each other. [Preview Abstract] |
Thursday, March 6, 2014 2:42PM - 2:54PM |
W33.00002: Momentum relaxation of a mobile impurity in a one-dimensional quantum gas Oleksandr Gamayun, Evgeni Burovski, Vadim Cheianov, Oleg Lychkovskiy We investigate the time evolution of the momentum of an impurity atom injected into a degenerate Tonks-Girardeau gas. We establish that given an initial momentum $p_0$ the impurity relaxes to a steady state with a non-vanishing momentum $p_{\infty}$. The nature of the steady state is found to be drastically different for integrable and non-integrable impurity models, which is due to multiple coherent scattering processes leading to a resonant interaction between the impurity and the host in the integrable case. The dependence of $p_{\infty}$ on $p_0$ remains non-trivial even in the limit of vanishing interaction between the impurity and host particles. In this limit $p_{\infty}(p_0)$ is found explicitly and the case of the external force applied to the impurity is analyzed as well. [Preview Abstract] |
Thursday, March 6, 2014 2:54PM - 3:06PM |
W33.00003: Transport induced dynamical flat-band phases in optical kagome lattices Chih-Chun Chien, Gia-Wei Chern, Massimiliano Di Ventra We consider quantum transport of ultracold fermions in an optical kagome lattice with a barrier keeping part of the lattice initially empty. The kagome lattice has two dispersive bands at low energy and one flat band at higher energy. When the barrier is removed, mobile atoms in the dispersive bands flow to the empty region. With atoms excited and removed by photons in the initially empty region, mobile atoms are depleted and a flat-band insulating phase emerges. Since the flat band of the kagome lattice is a high-energy one compared to the dispersive bands, this dynamically generated flat-band insulator is a population-inversion phase with no pumping required for maintaining it after its formation. In a similar setup a dynamical stripe phase emerges in the flat band when two-component fermions with weakly repulsive onsite interactions evolve in a static kagome lattice or even in the absence of interactions when the optical lattice is modulated. By considering nearest-neighbor repulsion, the system supports topologically non-trivial phases and their dynamics can be monitored at the mean-field level. [Preview Abstract] |
Thursday, March 6, 2014 3:06PM - 3:18PM |
W33.00004: Energy dissipation in drag dynamics of one-dimensional Fermi systems Jun'ichi Ozaki, Masaki Tezuka, Norio Kawakami We study the drag dynamics of a few fermions in a cloud of another fermion species in one-dimensional continuous systems, from interest in characteristic many-body effects in cold atom systems whose parameters change gradually in real time. We adopt the Fermi--Hubbard model and the time-dependent density matrix renormalization group method to calculate the energy cost needed to drag a trapped fermion cluster in a cloud of another type of fermions with contact interaction. We plot the energy cost per unit time as a function of the cloud density, and observe two peaks of the energy loss. This result provides, for example, the guide to reduce energy cost when one moves fermions in another type of fermion pool: move them independently or as a cluster. We explain the origin of the two peaks by using a schematic model which describes the detail of the excitation process. The peak in the small density region comes from the quasiparticle modes, while the other peak, in the large density region, corresponds to the collective mode of the whole cluster. [Preview Abstract] |
Thursday, March 6, 2014 3:18PM - 3:30PM |
W33.00005: An Interaction quench of strongly correlated heavy-light fermion mixtures khadijeh Najafi, Jim Freericks We use nonequilibrium dynamical mean-field theory to study the strongly correlated heavy-light fermion mixtures after making quench of its interaction parameter. We consider mixture of spinless heavy-light fermion at nonzero temperature and perform the sudden quench of the interaction parameter between the homogeneous metallic and insulating phase. Furthermore we present out result for the case of slow ramps and discuss about the possible optimized ramp for these system. We also discuss how close the system is to a thermal state after the quench of the interaction. [Preview Abstract] |
Thursday, March 6, 2014 3:30PM - 3:42PM |
W33.00006: Boson mediated collapse and revival of the Fermi sea in a Bose-Fermi mixture Deepak Iyer, Sebastian Will, Marcos Rigol The collapse and revival dynamics of quantum fields is one of the most pristine forms of nonequilibrium quantum dynamics. It has so far only been observed in the dynamical evolution of bosonic systems, such as coherent light or matter wave fields. We report on the first experimental observation of the collapse and revival of the Fermi sea in a Bose-Fermi mixture. The dynamics is generated by quenching the mixture to a deep 3D optical lattice and letting it evolve. To describe the observations, we develop an analytical model of the dynamics after the quench based on a spin-polarized Fermi sea that interacts with a coherent Bose-Einstein condensate. A remarkable outcome of the exact analytical solution is the robustness of the collapse and revival dynamics to the presence of an underlying confining potential in the initial state and/or during the time evolution, which suggests that such experiments can be used to accurately characterize interactions between bosons and fermions. Furthermore, the analytical solution makes apparent that the fermonic dynamics are independent of whether one starts with a bosonic coherent state or a collapsed Fock state with random occupation numbers. [Preview Abstract] |
Thursday, March 6, 2014 3:42PM - 3:54PM |
W33.00007: Log divergence in finite-size quantum Riemann metric Tiago Grangeiro Souza Barbosa Lima, Michael Kolodrubetz, Anatoli Polkovnikov We study the metric tensor, an object that describes distances between quantum states within a ground state manifold. Traditionally, it has been studied for changes in external parameters (e.g., magnetic field) at fixed system size. Here, we instead treat the system size as a tunable parameter and analyze the distance between wave functions at different system sizes. To emulate the effect of a change in the size of the system, we calculate the metric with respect to the position of a movable delta function potential, starting with the simplest case of free fermions. We find that the metric tensor diverges logarithmically with system size, similar to the entanglement entropy in a CFT. We also calculate the same metric tensor for the transverse field Ising model via perturbation theory, and comment on the relationship of our results to the spacetime metric in general relativity. [Preview Abstract] |
Thursday, March 6, 2014 3:54PM - 4:06PM |
W33.00008: Quench Dynamics of the Anisotropic Heisenberg Model Wenshuo Liu, Natan Andrei We develop an analytic approach for the study of the quench dynamics of the anisotropic Heisenberg model (XXZ model) on the infinite line. We present the exact time-dependent wavefunctions after a quench in an integral form for any initial state and for any anisotropy ? by means of a generalized Yudson contour representation. We calculate the evolution of several observables from two particular initial states: starting with a local N\`eel state we calculate the time evolution of the antiferromagnetic order parameter-staggered magnetization; starting with a state with consecutive flipped spins we calculate the propagation of magnons and bound state excitations, and the induced spin currents. We also show how the ``string'' solution of Bethe Ansatz equations emerge naturally from the contour approach. We confront our results with experiments and numerical methods where possible. [Preview Abstract] |
Thursday, March 6, 2014 4:06PM - 4:18PM |
W33.00009: Heating and decoherence from continuous measurement of the local density of lattice bosons Yariv Yanay, Erich Mueller, Mukund Vengalattore We explore the dynamics of a Bose Hubbard system when a weak local probe continuously measures the occupation of all sites. We find that this poissonian measurement process drives the system towards a thermodynamic distribution with high entropy. The final distribution does not depend on the interaction strength, but the time until steady-state does. Using a master equation for quantum observables, we calculate the heating rate and decoherence time for the system, and follow the time evolution of the two-point and four-point correlation functions in real and momentum space. [Preview Abstract] |
Thursday, March 6, 2014 4:18PM - 4:30PM |
W33.00010: Quantized Superfluid Vortex Rings in the Unitary Fermi Gas Michael Forbes, Aurel Bulgac, Michelle Kelley, Kenneth Roche, Gabriel Wlazowski In a recent article, Yefsah \textit{et al.} [Nature \textbf{499}, 426 (2013)] report the observation of an unusual excitation in an elongated harmonically trapped unitary Fermi gas. After phase imprinting a domain wall, they observe oscillations almost an order of magnitude slower than predicted by any theory of domain walls which they interpret as a ``heavy soliton'' of inertial mass some 200 times larger than the free fermion mass or 50 times larger than expected for a domain wall. We present compelling evidence that this ``soliton'' is instead a quantized vortex ring by showing that the main aspects of the experiment can be naturally explained within the framework of time-dependent superfluid DFT. [Preview Abstract] |
Thursday, March 6, 2014 4:30PM - 4:42PM |
W33.00011: Transverse Demagnetization Dynamics of a Unitary Fermi Gas Edward Taylor, Alma Bardon, Scott Beattie, Christopher Luciuk, William Cairncross, Daniel Fine, Nathan Cheng, Graham Edge, Shizhong Zhang, Stefan Trotzky, Joseph Thywissen Understanding the quantum dynamics of strongly interacting fermions is a challenge raised by diverse forms of matter, including high-temperature superconductors, neutron stars, and quark-gluon plasmas. An appealing benchmark is offered by cold atomic gases in the unitary limit of strong interactions, where the system is both scale-invariant and known to obey universal thermodynamics in equilibrium. Here we study the dynamics of a transversely magnetized unitary Fermi gas in an inhomogeneous magnetic field. We find that demagnetization is caused by diffusive spin transport with a diffusion constant that saturates at low temperatures to the conjectured quantum-mechanical lower bound $\hbar/m$, where $m$ is the particle mass. The development of pair correlations is observed by measuring Tan's contact parameter. [Preview Abstract] |
Thursday, March 6, 2014 4:42PM - 4:54PM |
W33.00012: Numerical generation of solitons, vortex rings, and vortices in an ultracold Fermi gas Peter Scherpelz, Karmela Padavic, Adam Rancon, Andreas Glatz, Igor Aranson, K. Levin Using the complex time-dependent Ginzburg Landau (TDGL) equation [1], we study quenches associated with phase imprinting, temperature sweeps and other density disturbances in three and two dimensional trapped Fermi gases. We consider variations in the TDGL equation due to the BCS-BEC crossover. While solitons are generally seen after the quenches, they are often accompanied by vortices and occasionally by vortex rings. Our work is partly motivated by the experimental observation of solitons in ultracold Fermi gases [2] which display both unusually slow oscillations and remarkable stability in a three-dimensional atomic gas. We discuss the stability and nature of the decay of these 3 types of collective superfluid inhomogeneities and their dependence on fluctuations, trap effects, and the trap aspect ratio. [1] A. Glatz, H. Roberts, I. Aranson, and K. Levin, PRB 84 180501 (2011). [2] T. Yefsah et al., Nature 499 426 (2013). [Preview Abstract] |
Thursday, March 6, 2014 4:54PM - 5:06PM |
W33.00013: Interacting Dark-Resonances for Sub-Natural Spectral Response: From Atoms to Meta-Atoms Pankaj Jha, Michael Mrejen, Jeongmin Kim, Chihhui Wu, Yuan Wang, Xiaobo Yin, Xiang Zhang Coherent interaction between dark-resonances have been extensively studied in atomic molecular and optical (AMO) physics to alter the interaction between atoms and electromagnetic fields. Here we theoretically investigate a classical analogue of interacting dark-resonance type physics in a plasmonic meta-molecule consisting of a radiative(bright) atom coupled to cascaded subradiant (dark) atoms. We theoretically demonstrate crude-damping limited absorptive response of the plasmonic molecule which also exhibits efficient excitation transfer within the elements. We provide numerical results in support of our analysis and develop an analytical description of the response of the meta-molecule in the limit of weak cascaded dark atoms coupling. The proposed scheme may be useful, in principle, for enhanced non-linearity, energy transport via coupled dark-resonances in plasmonics. [Preview Abstract] |
Thursday, March 6, 2014 5:06PM - 5:18PM |
W33.00014: Dynamics of Vector Solitons in Bose Einstein Condensates Majed O.D. Alotaibi, Lincoln D. Carr We analyze the dynamics of two-component vector solitons, namely bright-in-dark solitons, via variational approximations in Bose-Einstein condensates. We calculate the binding energy and the oscillation modes between the two components analytically for special cases. The variational approximation is based on hyperbolic secant (hyperbolic tangent) for the bright (dark) component, which leads to a system of ordinary differential equations for the evolution of the ansatz parameters. Analytical calculations are performed for same width components in the vector soliton, and numerical calculations extend the results to arbitrary widths. The system is described by a vector nonlinear Shr\"odinger equation appropriate to the mean field theory of Bose-Einstein condensates [Preview Abstract] |
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