Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session V32: Optical Lattices |
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Sponsoring Units: DAMOP Chair: Chris Oates, National Institute of Standards and Technology, Boulder Room: Colorado Convention Center 402 |
Thursday, March 8, 2007 11:15AM - 11:27AM |
V32.00001: Ion Chains in Optical Lattices as Simple Quantum Glasses Roman Schmied, Tommaso Roscilde, Diego Porras, Ignacio Cirac We propose the loading of linearly trapped ions onto an intense optical lattice. In the limit of a deep lattice, we recover a classical one-dimensional Coulomb lattice gas in a harmonic trap. This system exhibits glassiness, due to significant metastability in its translational degrees of freedom. Quantum fluctuations can be induced at will by lowering the lattice amplitude, which allows for the controlled realization of a quantum glassy system. We study the dynamics of such systems during thermal and quantum annealing, and discuss how the effects of glassiness can be observed in the currently available experimental ion-trap setups. [Preview Abstract] |
Thursday, March 8, 2007 11:27AM - 11:39AM |
V32.00002: Predicted quantum stripe ordering in optical lattices Congjun Wu, W. Vincent Liu, Joel Moore, Sankar Das Sarma We predict the robust existence of a novel quantum orbital stripe order in the $p$- band Bose-Hubbard model of two-dimensional triangular optical lattices with cold bosonic atoms. An orbital angular momentum moment is formed on each site exhibiting a stripe order both in the superfluid and Mott-insulating phases. The stripe order spontaneously breaks time-reversal, lattice translation and rotation symmetries. In addition, it induces staggered plaquette bond currents in the superfluid phase. Possible signatures of this stripe order in the time of flight experiment are discussed. [Preview Abstract] |
Thursday, March 8, 2007 11:39AM - 11:51AM |
V32.00003: BCS-BEC crossover on the two dimensional honeycomb lattice Erhai Zhao, Arun Paramekanti We study the attractive Hubbard model on a honeycomb lattice. At half-filling, we find a quantum critical point (QCP) separating a weakly interacting semimetal with massless Dirac fermions from a strong coupling s-wave superconducting state. Away from half-filling, this model exhibits a BCS-BEC crossover in the vicinity of this QCP. Studying this model using ultracold atoms in an optical lattice could shed light on quantum phase transitions and BCS-BEC crossovers in electronic models. We present results for the evolution of several observables through the BCS-BEC crossover at zero temperature -- the Fermi surface, the superfluid density and the collective sound and Leggett modes. We also suggest a method to observe the Leggett mode in an optical lattice. [Preview Abstract] |
Thursday, March 8, 2007 11:51AM - 12:03PM |
V32.00004: Mixture of bosonic and spin-polarized fermionic atoms in an optical lattice Lode Pollet, Corinna Kollath, Ulrich Schollw\"ock, Matthias Troyer We investigate the properties of Bose-Fermi mixtures for experimentally relevant parameters in one dimension using numerical methods. The effect of the fermions on the bosons is not only to deepen the parabolic trapping potential, but also to reduce the bosonic repulsion in higher order. This reduction would theoretically lead to an increase in the bosonic visibility. The opposite was observed however in the experimental ${}^{87}$Rb - ${}^{40}$K systems, most likely due to a sharp rise in temperature. We discuss the features which could be observed experimentally if temperature remains low, such as a bosonic Mott insulator transition driven by the fermionic concentration, and the formation of various composite particles. [Preview Abstract] |
Thursday, March 8, 2007 12:03PM - 12:15PM |
V32.00005: Coexistence of superfluid and Mott phases of strongly-interacting lattice bosons Courtney Lannert, Roman Barankov, Smitha Vishveshwara Recent experiments on strongly-interacting bosons in optical lattices [1,2] have revealed the co-existence of spatially-separated Mott-insulating and number-fluctuating phases in the presence of an external trapping potential. Employing a simple theoretical model [3], we obtain an effective description of the superfluid state trapped between the Mott states. We calculate the collective excitation spectrum of such a superfluid and its critical temperature, and discuss the crossover between two- and three-dimensional behavior of its thermal properties as a function of the lattice parameters. \newline [1] S.~F\"olling, A.~Widera, T.~M\"uller, F.~Gerbier, and I.~Bloch, Phys. Rev. Lett. {\bf 97}, 060403 (2006). \newline [2] G.~K.~Campbell, J.~Mun, M.~Boyd, P.~Medley, A.~E.~Leanhardt, L.~Marcassa, D.~E.~Pritchard, and W.~Ketterle, Science {\bf 313}, 649 (2006). \newline [3] R.~A.~Barankov, C.~Lannert, and S.~Vishveshwara, cond-mat/0611126. [Preview Abstract] |
Thursday, March 8, 2007 12:15PM - 12:27PM |
V32.00006: Noise spectroscopy for detecting multi-atomic composite states in optical lattices Henning Moritz, Anatoly Kuklov We propose and discuss methods \footnote[1]{A.B. Kuklov, H. Moritz, cond-mat/0609531} for detecting quasi-molecular complexes which are expected to form in strongly interacting optical lattice systems. Particular emphasis is placed on the detection of composite fermions forming in Bose-Fermi mixtures. We argue that, as an indirect indication of the composite fermions and a generic consequence of strong interactions, periodic correlations must appear in the atom shot noise of bosonic absorption images, similar to the bosonic Mott insulator \footnote[2]{S. F\"olling, et al., Nature {\bf 434}, 481 (2005)}. The composites can also be detected directly and their quasi-momentum distribution measured. This method -- an extension of the technique of noise correlation interferometry \footnote[3]{E. Altman et al., Phys. Rev. A {\bf 79}, 013603 (2004)} -- relies on measuring higher order correlations between the bosonic and fermionic shot noise in the absorption images.The method is expected to work well for fermionic composites consisting of less than four atoms and for bosonic ones consisting of less than six atoms. Above these numbers, the uncorrelated noise becomes too large. [Preview Abstract] |
Thursday, March 8, 2007 12:27PM - 12:39PM |
V32.00007: Dynamics of multicomponent Bose-Einstein condensates on two- and three-dimensional optical lattices R. Mark Bradley, L.D. Carr, J.E. Bernard Exact solutions to the mean field equations of motion are constructed for multicomponent Bose-Einstein condensates on square, rectangular and simple cubic optical lattices. For two condensates on a rectangular optical lattice, we find temporally-periodic solutions in which the optical lattice is divided into two sublattices, and the condensates oscillate back and forth between these sublattices. For a square optical lattice, a solution is found in which single condensate moves in a checkerboard vortex-antivortex array. We also obtain fascinating solutions for two condensates in which the square optical lattice is divided into a total of four sublattices, and the condensates move cyclically between these sublattices. Stationary solutions of high symmetry are constructed for two, three and four condensates on a simple cubic optical lattice. Finally, the stability of the solutions in two dimensions is probed thorough numerical integrations of the mean field equations of motion. [Preview Abstract] |
Thursday, March 8, 2007 12:39PM - 12:51PM |
V32.00008: Analysis of the coherence time of a Bose-Einstein-condensate interferometer with optical control of dynamics James Stickney, Dana Z. Anderson, Alex Zozulya Atom interferometers using Bose-Einstein condensate that is confined in a waveguide and manipulated by optical pulses have been limited by their short coherence times. We present a theoretical model that offers a physically simple explanation for the loss of contrast and propose the method for increasing the fringe contrast by recombining the atoms at a different time. A simple, quantitatively accurate, analytical expression for the optimized recombination time is presented and used to place limits on the physical parameters for which the contrast may be recovered. [Preview Abstract] |
Thursday, March 8, 2007 12:51PM - 1:03PM |
V32.00009: Pairing and density-wave phases in Fermion-Boson mixtures at fixed filling Filippos Klironomos, Shan-Wen Tsai We study a mixture of fermionic and bosonic cold atoms on a two-dimensional optical lattice, where the fermions are prepared in two hyperfine (isospin) states and the bosons have Bose-Einstein condensed (BEC). The coupling between the fermionic atoms and the bosonic fluctuations of the BEC has similarities with electron-phonon couplings in crystals. We study the phase diagram for this system at fixed fermion density of one per site (half-filling). We find that tuning of the lattice parameters and interaction strengths (for fermion-fermion, fermion-boson and boson-boson interactions) drives the system to undergo antiferromagnetic ordering, s-wave and d-wave pairing superconductivity or a charge density wave phase. We use functional renormalization group analysis where retardation effects are fully taken into account by keeping the frequency dependence of the the interaction vertices and self-energies. We calculate response functions and also provide estimates of the energy gap associated with the dominant order, and how it depends on different parameters of the problem. [Preview Abstract] |
Thursday, March 8, 2007 1:03PM - 1:15PM |
V32.00010: Quantum Monte Carlo simulations of resonantly interacting ultracold atoms Valy Rousseau, Peter Denteneer A one-dimensional Hubbard-like model with a term describing conversion of two atoms into a bound state (``molecule'') is presented. This model is thought to be relevant for ultra-cold atoms in an optical lattice, interacting via a Feshbach resonance. The model is solved exactly by means of Quantum Monte Carlo simulations, which allow for the measurement of physical quantities of interest, such as the superfluid density and (quasi)condensate fraction. The calculated momentum distribution function is directly comparable with experiments. Results are also confronted with mean-field theory which may be expected to give a poorer description of quantum fluctuations, especially for one-dimensional systems. [Preview Abstract] |
Thursday, March 8, 2007 1:15PM - 1:27PM |
V32.00011: Systematic Ground-state Exploration for Strongly-interacting Fermions Loaded on Optical Lattices Masahiko Machida, Yoji Ohashi, Hideki Matsumoto, Susumu Yamada We systematically investigate ground state properties and effects of an optical lattice potential in one- and two-dimensional two-component trapped Fermi gases with the same population. Using an exact diagonalization method and a density-matrix renormalization group technique, we calculate the ground state many-body wave-function, as well as the density profile, as a function of the strength of an attractive interaction. We show that fine inhomogeneous zigzag patterns universally emerge in the above models under the presence of attractive on-site interaction and trap potential Theoretical and numerical analyses suggest that these structures originate from an effective repulsive interaction between tightly-bound pairs and a breakdown of translational invariance. Furthermore, it is emphasized that the pattern obtained numerically in the 2-D model is the checkerboard type, which is very similar to results recently observed in a vortex core of High-Tc cuprate superconductor. In the presentation, we will touch imbalanced cases, too. [Preview Abstract] |
Thursday, March 8, 2007 1:27PM - 1:39PM |
V32.00012: Two Critical velocities for a superfluid in a periodic potential Biao Wu, Junren Shi In contrast to a homogeneous superfluid which has only one critical velocity, there exist two critical velocities for a superfluid in a periodic potential. The first one, which we call inside critical velocity, is for a macroscopic impurity to move frictionlessly in the periodic superfluid system; the second, which is called trawler critical velocity, is the largest velocity of the lattice for the superfluidity to maintain. The result is relevant to the superfluidity observed in the Bose-Einstein condensate in an optical lattice and supersolid helium. [Preview Abstract] |
Thursday, March 8, 2007 1:39PM - 1:51PM |
V32.00013: Finite-size effects and entanglement in ultracold atoms on optical lattices L. D. Carr$^{2,3}$, R. C. Brown$^{2,3}$, D. G. Schirmer$^{2,3}$, R. V. Mishmash$^2$, S. P. Santos$^2$, I. Danshita$^3$, J. E. Williams$^3$, Charles W. Clark$^3$ We study finite size effects in the phase diagrams of a number of Fermi-, Bose-, and Fermi-Bose-Hubbard Hamiltonians relevant to ultracold atoms in one dimension. Both exact numerical solutions and approximations via Vidal's algorithm (Time Evolving Block Decimation) are utilized. We characterize excited states by their entanglement, in particular comparing three entanglement measures: the entropy of entanglement, Meyer's Q-measure, and the Schmidt number. We show that the phase diagrams and the entanglement structure of excited eigenstates as a function of the Hamiltonian parameters depends strongly on the number of sites and the dimensionality of on-site Hilbert space. These results are vital for experiments on small systems, as they differ greatly from what is found in the thermodynamic limit. [Preview Abstract] |
Thursday, March 8, 2007 1:51PM - 2:03PM |
V32.00014: Quantum Entangled Dark Solitons in the Bose-Hubbard Model R.V. Mishmash, L.D. Carr We investigate the existence and stability of dark quantum solitons formed by Bose-Einstein condensates in a one-dimensional optical lattice. This is done by employing a one-level Bose-Hubbard model and simulating the real time dynamics of the condensate using both exact numerical techniques and Vidal's simulation method, i.e., Time Evolving Block Decimation. For the initial condition, we take a Gutzwiller ansatz wavefunction with on-site truncated coherent states and build a direct quantum analog to the soliton solutions of the Discrete Nonlinear Schr\"{o}dinger Equation. The stability of these solutions are then analyzed in the Bose-Hubbard model for different parameter regimes. We are especially interested in the behavior of dark solitons near the Mott-superfluid border. Also, we quantitatively examine the effect of quantum entanglement on dark quantum soliton stability. [Preview Abstract] |
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