Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session W43: Focus Session: Cold Atoms in Optical Lattices |
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Sponsoring Units: DAMOP GQI Chair: S. das Sarma, University of Maryland Room: Baltimore Convention Center 346 |
Thursday, March 16, 2006 2:30PM - 2:42PM |
W43.00001: Macroscopic Quantum Tunneling and Entangled States in Bose-Einstein Condensates Lincoln D. Carr, Dimitri R. Dounas-Frazer, Ann M. Hermundstad We use a multi-band Hubbard model to study beyond-mean-field effects in macroscopic quantum tunneling of excited states in Bose-Einstein condensates. Our goal is to determine straightforward observables such as the oscillation frequency of kink-like structures between two wells or the propagation speed of such structures on a lattice. As a preliminary step, we present some surprising new results for entangled states of N bosons in two wells. [Preview Abstract] |
Thursday, March 16, 2006 2:42PM - 2:54PM |
W43.00002: Disorder-induced enhancement of phase coherence in trapped bosons on optical lattices Pinaki Sengupta, Aditya Raghavan, Stephan Haas Using numerical methods, we have investigated the effects of disorder on a system of interacting bosons trapped in a one-dimensional optical lattice. Our results show that there is a unique effect at small to moderate strengths of disorder if there is a Mott plateau at the center of the trap in the ordered system - long range phase coherence actually {\it increases} as a result of disorder. The localization effects due to correlation and disorder compete against each other which results in a partial delocalization of the particles in the Mott region leading to increased coherence. Eventually, at large disorder strengths, the phase coherence decreases. In the absence of a Mott plateau at the center, this effect is absent and the phase coherence decreases for all disorder strenghts. Further analysis of the uniform (no trap) system shows that the disordered states belong to the Bose glass phase. [Preview Abstract] |
Thursday, March 16, 2006 2:54PM - 3:06PM |
W43.00003: Cold Atom Optical Lattices as Quantum Analog Simulators for Aperiodic One-Dimensional Localization Without Disorder Vito Scarola, Sankar Das Sarma Cold atom optical lattices allow for the study of quantum localization and mobility edges in a disorder-free environment. We predict the existence of an Anderson-like insulator with sharp mobility edges in a one-dimensional nearly-periodic optical lattice. We show that the mobility edge manifests itself as the early onset of pinning in center of mass dipole oscillations in the presence of a magnetic trap which should be observable in optical lattices. This work is supported by NSA-LPS and ARO-ARDA. [Preview Abstract] |
Thursday, March 16, 2006 3:06PM - 3:42PM |
W43.00004: Measuring correlation functions in interacting systems of cold atoms Invited Speaker: I will discuss two approaches to measuring correlation functions in experiments with cold atoms. The first approach is based on analyzing atom shot noise in the time of flight experiments. I will compare this approach to Hanburry-Brown-Twiss experiments and show that it can be used to probe novel quantum states of cold atoms including paired states of fermions and magnetically ordered states in optical lattices. The second approach relies on interference experiments between extended condensates. I will show that the interference pattern contains information about correlation functions within individual condensates and that the full distribution of the fringe contrast provides information about high order correlation functions. I will discuss possible applications of this method to study Luttinger liquid behavior in one dimensional systems and probe Kosterlitz-Thouless transition in two dimensional condensates. [Preview Abstract] |
Thursday, March 16, 2006 3:42PM - 3:54PM |
W43.00005: Feshbach resonances in optical lattices Dennis Dickerscheid In the last few years there has been much excitement in the field of ultracold atomic gases. In a large amount this is due to the use of so-called Feshbach resonances and, in addition, the use of an optical lattice for the atoms. Recently, the first steps have been made to experimentally combine these techniques, which can both be used to tune the interactions between the atoms. Motivated by these developments, we show that the physics of these systems is described by a generalized Hubbard model for which the microscopic parameters are determined by the details of the lattice and the experimentally known parameters of the Feshbach resonance in the absence of the optical lattice. As a particular application we also discuss the phasediagrams of a Bose gas and a Bose-Fermi mixture near a Feshbach resonance in an optical lattice. [Preview Abstract] |
Thursday, March 16, 2006 3:54PM - 4:06PM |
W43.00006: Ramping Fermions in Optical Lattices across a Feshbach resonance Aniello Esposito, Helmut G. Katzgraber, Matthias Troyer We study the properties of ultracold Fermi gases in a three-dimensional optical lattice when crossing a Feshbach resonance. By using a zero-temperature formalism, we show that three-body processes are enhanced in a lattice system in comparison to the continuum case. This poses one possible explanation for the short molecule lifetimes found when decreasing the magnetic field across a Feshbach resonance. Effects of finite temperatures on the molecule formation rates are also discussed by computing the fraction of double-occupied sites. Our results show that current experiments are performed at temperatures considerably higher than expected: lower temperatures are required for fermionic systems to be used as quantum simulators. In addition, by relating the double occupancy of the lattice to the temperature, we provide a means for thermometry in fermionic lattice systems, previously not accessible experimentally. The effects of ramping a filled lowest band across a Feshbach resonance when increasing the magnetic field are also discussed: fermions are lifted into higher bands due to entanglement of Bloch states. Our results are in good agreement with recent experiments. [Preview Abstract] |
Thursday, March 16, 2006 4:06PM - 4:18PM |
W43.00007: Competing phases in Bose-Fermi mixtures of ultracold atoms in optical lattices Ludwig Mathey, Shan-Wen Tsai, Antonio Castro-Neto We study mixtures of ultracold bosonic and fermionic atoms, confined to a two-dimensional lattice, with a numerical functional renormalization group (RG) method. The method is an extension of the RG approach to interacting fermions\footnote{R. Shankar, Rev. Mod. Phys. 66, 129 (1994).} which also takes into account couplings of the fermions to bosonic modes.\footnote{S.-W. Tsai, A. H. Castro Neto, R. Shankar, and D. K. Campbell, Phys. Rev. B 72, 054531 (2005).} We obtain the phase diagram of the system for the limit of large bosonic phonon velocity in comparison to the Fermi velocity. The renormalization group method provides the value of the gaps of the various phases, as well as the subdominant orders and the short range fluctuations. [Preview Abstract] |
Thursday, March 16, 2006 4:18PM - 4:30PM |
W43.00008: Vidal’s simulation method applied to two coupled 1D lattices James Williams, Ippei Danshita, Charles Clark Recently, a method was developed employing matrix product states to simulate the quantum dynamics of a one dimensional lattice system using an adaptive time stepping technique [G. Vidal, Phys. Rev. Lett. 91, 147902 (1993); Phys. Rev. Lett. 93, 040502 (1994)]. We use this approach to simulate the dynamics of bosons loaded into a double-well optical lattice geometry relevant to recent experiments at NIST [I. Spielman et al., Bull. Am. Phys. Soc. (2005)]. We study a pair of coupled 1D lattices, which can be mapped into a single 1D lattice with next-nearest neighbor interactions. [Preview Abstract] |
Thursday, March 16, 2006 4:30PM - 4:42PM |
W43.00009: The speed of sound in a Bose-Einstein condensate in optical lattices Biao Wu, Zhaoxin Liang, Xi Dong We have studied the speed of sound of a Bose-Einstein condensate in optical lattices both analytically and numerically. We find that in the one-dimensional case, the speed of sound falls monotonically with increasing lattice strength. However, the trends are different in two and three dimensional cases. In these two cases, when the interaction is strong, the speed of sound also decreases monotonically with increasing lattice strength. But when the interaction is weak, the sound speed first increases then decreases when the lattice strengh increases. [Preview Abstract] |
Thursday, March 16, 2006 4:42PM - 4:54PM |
W43.00010: Instability of a superfluid Bose gas induced by a locked thermal gas in an optical lattice Satoru Konabe, Tetsuro Nikuni We use a dissipative Gross-Petaevskii equation derived from the Bose-Hubbard Hamiltonian to study the effect of the thermal component on the stability of a current-carrying superfluid state of a Bose gas in an optical lattice potential. We explicitly show that the superfluid state becomes unstable at certain quasi-momentum of the condensate due to a thermal component which is locked by an optical lattice potential. It is shown that this instability coincides with the Landau instability derived from the GP equation. [Preview Abstract] |
Thursday, March 16, 2006 4:54PM - 5:06PM |
W43.00011: Imaging of diverging correlations close to a quantum phase transition in optical lattices A.B. Kuklov, Q. Niu, I. Carusotto We suggest real space determination of diverging space-time correlations close to a quantum phase transition from Bose Mott insulator to superfluid in optical lattices. The method relies on interference of either the released cloud or the outcoupled atomic beam with some reference Bose-Einstein condensate. Upon approaching the transition from the Mott phase, the resulting interference pattern represents a set of uncorrelated domains, with a typical size determined by the correlation length $\xi$ as long as it is smaller than a system size $L$. Repetition of the measurements in a progression of $L$ for $\xi > L$ provides crucial information on the critical behavior in the context of the finite size scaling approach. The Hanbury Brown \& Twiss type measurements allow extracting the average spatial correlator, which is insensitive to the expansion time and decaying on distances $\approx \xi$ (for $\xi < L$). The non- destructive scheme employing two outcoupling pulses separated by some time $\tau$ can probe both the spatial and time correlations. [Preview Abstract] |
Thursday, March 16, 2006 5:06PM - 5:18PM |
W43.00012: Attractive Bosons in Optical Lattices Daniel Goldbaum, Erich Mueller We study the theory of attractive bosons in an optical lattice with a hard-core constraint, limiting on-site occupations to 0, 1, or 2 particles per site. Our goal is to investigate the Boson pairing phase transition. We describe how an off-resonant Raman photoassociation transition [C. Ryu, et. al. Cond-mat/0508201] may be used to generate this model. We explore the properties of this system through a mean-field theory that allows short-range correlations. We write a wavefunction that describes both atomic and molecular superfluid phases, and study properties of the system near the phase transition, including the structure of vortices. [Preview Abstract] |
Thursday, March 16, 2006 5:18PM - 5:30PM |
W43.00013: The repulsive interacting bosons in an one dimensional moving lattice ring Qi Zhou, Tin-Lun Ho We investigate the properties of the ground state of the repulsive interacting bosons in an one dimensional moving lattice ring, and reveal that the superfluid density of the system is a periodic function of the velocity of the lattice. In the weakly interacting limit, the Umklapp process of the mutual scattering of bosons in the moving lattice provide the generation mechanism for the vortices. In the strongly interacting limit, the moving lattice can cause transitions between the Mott insulator and the different superfluid phases carrying vortex with different winding number. [Preview Abstract] |
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