Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session P31: Ultracold Gases in One Dimensional and Ring Geometries |
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Sponsoring Units: DAMOP Chair: Yu-Ju Lin, National Institute of Standards and Technology Room: E141 |
Wednesday, March 17, 2010 8:00AM - 8:12AM |
P31.00001: Phase-fluctuating regime of a ring-shaped Bose-Einstein condensate Ludwig Mathey, Anand Ramanathan, Kevin Wright, Sergio Muniz, William Phillips, Charles Clark We study the phase-fluctuating condensate regime of ultra-cold atoms trapped in a ring-shaped geometry. We first consider a simplified box geometry, in which we identify the conditions to create a state that is dominated by thermal phase-fluctuations, and then explore the actual experimental geometry. We also address possible ways of detecting this regime. [Preview Abstract] |
Wednesday, March 17, 2010 8:12AM - 8:24AM |
P31.00002: Nonequilibrium dynamics of bosonic supercurrents in a two coupled ring geometry: Nonergodicity and current self trapping Rafael Hipolito, Anatoli Polkovnikov Interacting systems do not always exhibit ergodic behavior, as it was first observed in the seminal work of Fermi, Pasta, and Ulam (FPU). Subsequently, it was found that many such systems exhibiting nonergodicity have a special property known as integrability, where the system has as many conserved quantities as degrees of freedom. These systems can exhibit interesting quasiperiodic dynamics (e.g. near revival of the initial nonequilibrium state), in stark contrast to the essentially chaotic dynamics experienced in systems out of equilibrium. Most of the focus in these studies has been on classical integrable systems. In this talk we analyze dynamics of bosonic supercurrents in a two coupled ring geometry. We find that in the classical (Gross-Pitaevskii) limit the dynamics very closely resembles that of FPU system suggesting that these phenomena can be experimentally probed in cold atom systems. We also show that weak quantum fluctuations suppress long time revivals leading to more ergodic behavior. [Preview Abstract] |
Wednesday, March 17, 2010 8:24AM - 8:36AM |
P31.00003: Metastable states and macroscopic quantum tunneling in a cold atom Josephson ring Dmitry Solenov, Dmitry Mozyrsky We study macroscopic properties of a system of weakly interacting neutral bosons confined in a ring-shaped potential with a Josephson junction. We derive an effective low energy action for this system and evaluate its properties. In particular we find that the system possesses a set of metastable current-carrying states and evaluate the rates of transitions between these states due to macroscopic quantum tunneling. Finally we discuss signatures of different metastable states in the time-of-flight images and argue that the effect is observable within currently available experimental technique. [Preview Abstract] |
Wednesday, March 17, 2010 8:36AM - 8:48AM |
P31.00004: Quantum Entangled Dark Solitons Lincoln D. Carr, Ryan V. Mishmash, Ippei Danshita, Charles W. Clark We present a fully quantum many-body treatment of dark solitons formed by ultracold bosonic atoms in one-dimensional optical lattices [1,2]. Using time-evolving block decimation to simulate the single-band Bose- Hubbard Hamiltonian, we consider the quantum dynamics of density- and phase-engineered dark solitons as well as the quantum evolution of mean-field dark solitons injected into the quantum model. Quantum fluctuations cause the dark soliton to fill in and can induce an inelasticity in soliton-soliton collisions. Comparisons are made to the Bogoliubov theory which predicts depletion into an anomalous mode that fills in the soliton. Our many-body treatment allows us to go beyond the Bogoliubov approximation and calculate explicitly the dynamics of the system's natural orbitals. [1] Phys. Rev. Lett. {\bf 103}, 140403 (2009). [2] Phys. Rev. A {\bf 80}, 053612 (2009). [Preview Abstract] |
Wednesday, March 17, 2010 8:48AM - 9:00AM |
P31.00005: Electronic properties of a harmonically confined 1D Hubbard model Stefan Soeffing, Sebastian Eggert Ultra-cold gases in optical lattices provide an excellent experimental playground to study the Hubbard model in one dimension. While lots of theoretical results are available for periodic or open boundary conditions the effect of a harmonic trapping potential is not always clear. In this talk we investigate the low-temperature properties of the Hubbard model in a harmonic potential using Luttinger liquid theory combined with numerical Density Matrix Renormalization Group (DMRG) calculations at low fillings. Interaction effects are analyzed in the context of oscillations in the charge density and local density of states. [Preview Abstract] |
Wednesday, March 17, 2010 9:00AM - 9:12AM |
P31.00006: Exact thermodynamics of the Gaudin-Yang Fermi gas Erhai Zhao, Xi-Wen Guan, W. Vincent Liu, M. T. Batchelor, Masaki Oshikawa We study the thermodynamics of the Gaudin-Yang model, a one- dimensional attractive Fermi gas with spin imbalance recently realized in cold atoms experiments. The exact thermodynamic Bethe ansatz equations are simplified to four algebraic equations in the experimental regime of strong interaction and relatively low temperature. Using the new formulation, we discuss the qualitative features of finite-temperature crossover and make quantitative predictions on the density profiles in traps. These results can help to achieve accurate thermometry for trapped spin-imbalanced Fermi gases with strong interaction. [Preview Abstract] |
Wednesday, March 17, 2010 9:12AM - 9:24AM |
P31.00007: ABSTRACT WITHDRAWN |
Wednesday, March 17, 2010 9:24AM - 9:36AM |
P31.00008: Ground-state properties of a Tonks-Girardeau gas in a periodic potential Bo-Bo Wei, Shi-Jian Gu, Hai-Qing Lin We investigate the ground-state properties of a bosonic Tonks-Girardeau (TG) gas confined in a one-dimensional periodic potential. The single-particle reduced density matrix is computed numerically for systems up to $N$=265 bosons. Scaling analysis of the occupation number of the lowest orbital shows that there are no Bose-Einstein condensation (BEC) for the periodically trapped TG gas in both commensurate and incommensurate cases. We find that, in the commensurate case, the scaling exponents of the occupation number of the lowest orbital, the amplitude of the lowest orbital and the zero-momentum peak height with the particle numbers are 0, 0.5 and 1, respectively, while in the incommensurate case, they are 0.5, 0.5 and 1.5, respectively. These exponents are related to each other in a universal relation. [Preview Abstract] |
Wednesday, March 17, 2010 9:36AM - 9:48AM |
P31.00009: Particle-Hole Asymmetry and Brightening of Solitons in a Strongly Repulsive BEC Indubala Satija, Radha Balakrishnan, Charles Clark We study solitary wave propagation in the condensate of a system of hard-core bosons with nearest-neighbor interactions. For this strongly repulsive system, the evolution equation for the condensate order parameter of the system, obtained using spin coherent state averages is different from the usual Gross-Pitaevskii equation (GPE). The system is found to support two kinds of solitons when there is a particle-hole imbalance: a dark soliton that dies out as the velocity approaches the sound velocity, and a new type of soliton which brightens and persists all the way up to the sound velocity, transforming into a periodic wave train at supersonic speed. Analogous to the GPE soliton, the energy-momentum dispersion for both solitons is characterized by Lieb II modes. [Preview Abstract] |
Wednesday, March 17, 2010 9:48AM - 10:00AM |
P31.00010: Dielectric breakdown of Mott insulators and the many-body Schwinger mechanism studied with the generalized Bethe ansatz Takashi Oka, Hideo Aoki The dielectric breakdown may be regarded as a condensed matter realization of the Schwinger mechanism - creation of electron-positron pairs by electric fields - in which the threshold for breakdown is considerably reduced due to a quantum leakage of the wave function. In Mott insulators, a many-body counterpart of this phenomena is shown to take place, which is here studied with the quantum tunneling formalism due to Dykhne-Davis-Pechukas as applied to the one-dimensional Hubbard model. We implement this for the quantum tunneling rate with an analytic continuation of the Bethe-ansatz solution for excited states to a non-Hermitian case. This enables us to extend the many- body Landau-Zener picture to the thermodynamic limit, with a remarkable agreement with the time-dependent density matrix renormalization group result. (arXiv:0903.2707) [Preview Abstract] |
Wednesday, March 17, 2010 10:00AM - 10:12AM |
P31.00011: Luttinger liquid of trimers in the asymmetric Fermi Hubbard model Giuliano Orso, Evgeni Burovski, Thierry Jolicoeur We investigate attractive fermions in a one dimensional optical lattice with unequal tunneling rates [1]. Due to the mass asymmetry, the microscopic model is not integrable and multi-particle bound states appear. We focus on trimers, namely three-body bound state made of one light and two heavy fermions. We first present the exact solution of the three-body problem, yielding the binding energy and the effective mass of a single trimer. Based on DMRG simulations, we then show that trimers can open an energy gap at finite commensurate densities, leading to a suppression of superconducting correlations and topological changes in the grand-canonical phase diagram. [1] G. Orso, E. Burovski and T. Jolicoeur, arXiv:0907.1533 [Preview Abstract] |
Wednesday, March 17, 2010 10:12AM - 10:24AM |
P31.00012: Particle-hole symmetric localization in optical lattices using time modulated random on-site potentials Yue Zou, Ryan Barnett, Gil Refael For ultra-cold atoms in optical lattices, periodically driven potentials provide a novel way to tune the model parameters. Well-studied examples include the so-called ``dynamical localization'' phenomenon, where a uniform periodically modulating potential effectively reduces the hopping strength, which can be used to tune a condensate through the superfluid-insulator-transition or to observe photon-assisted tunneling of a condensate. Here we propose a novel application of the periodically driven potential: with disordered on-site potential and weak uniform hopping amplitude, one can tune a non-interacting system from an Anderson insulator to a random hopping model with diverging localization length at the band center, and eventually to a uniform-hopping tight-binding model if the oscillation frequency of the potential energy is gradually increased from zero to infinity. Detailed study of the one-dimensional case will be reported. [Preview Abstract] |
Wednesday, March 17, 2010 10:24AM - 10:36AM |
P31.00013: The fate of 1D spin-charge separation away from Fermi points Thomas Schmidt, Adilet Imambekov, Leonid Glazman The momentum-resolved dynamic responses of a one-dimensional (1D) electron liquid are singular at the spectrum of the lowest-energy excitation branch, ie. at the spinon spectrum. These power-law singularities survive at arbitrary momentum. We express the corresponding exponents in terms of the spinon spectrum. Special attention is paid to the electron spectral function measured in tunneling experiments. [Preview Abstract] |
Wednesday, March 17, 2010 10:36AM - 10:48AM |
P31.00014: Predicted mobility edges in one-dimensional incommensurate optical lattices John Biddle, Sankar Das Sarma Localization properties of non-interacting quantum particles in one-dimensional incommensurate lattices are investigated with an exponential short-range hopping that is beyond the minimal nearest-neighbor tight-binding model. Energy dependent mobility edges are analytically predicted in this model and verified with numerical calculations. The results are then mapped to the continuum Schr\"odinger equation, and an approximate analytical expression for the localization phase diagram and the energy dependent mobility edges in the ground band is obtained. [Preview Abstract] |
Wednesday, March 17, 2010 10:48AM - 11:00AM |
P31.00015: Many-body localization transition of one-dimensional interacting hard-core bosons in a random potential Arijeet Pal, David Huse We use exact diagonalizations to explore the properties of the exact many-body eigenstates of this model. The model can also be viewed as the spin-1/2 Heisenberg chain with a static random field along the z-direction. We explore the correlation functions within each of the eigenstates, looking at all states and thus effectively working at infinite temperature. For weak random potential the correlations are consistent with the eigenstates being thermal, as expected in this nonlocalized, ergodic phase. For strong random potential the eigenstates are localized, with very little entanglement. We roughly locate the many-body localization transition and explore the finite-size scaling and the probability distributions of the correlations, in particular asking the question of whether this transition is more consistent with conventional or with infinite-randomness scaling. [Preview Abstract] |
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