Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session S4: Disordered Quantum Gases |
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Sponsoring Units: DAMOP Chair: Yong Chen, Rice University Room: Colorado Convention Center Korbel 2B-3B |
Wednesday, March 7, 2007 2:30PM - 3:06PM |
S4.00001: Ultracold Atoms in Optical Potentials and Novel Quantum Phases Invited Speaker: The experimental study of ultracold atoms in optical lattices has thrown a bridge between the realms of atomic physics and solid state physics. Laser beams in standing wave configuration provide ideal periodic potentials for the atoms, thus constituting a test ground for the quantum theory of transport in periodic structures. On the other hand, laser light can also be used to engineer controlled disorder in the form of speckle fields or multi-chromatic lattices with incommensurate wavelengths. These aperiodic potentials can be used to study the physics of disordered systems and the emergence of quantum localization phases, such as Anderson insulators or strongly interacting Bose Glass phases. I will review some of the latest advances in this exciting field, discussing experiments with quantum degenerate gases in disordered optical potentials. [Preview Abstract] |
Wednesday, March 7, 2007 3:06PM - 3:42PM |
S4.00002: Localisation of interacting Bose-Einstein Condensates expanding in a 1D random potential created by laser speckle Invited Speaker: We have studied the 1D expansion of a coherent interacting matter wave (a Bose-Einstein condensate) in the presence of disorder. Well controlled 1D random potentials are produced with laser speckle patterns. We observe the suppression of the transport of the BEC in the random potential, and we study this localisation phenomenon as a function of the parameters of the random potential. A theoretical analysis and numerical simulations allow us to interpret the observed behaviours. [Preview Abstract] |
Wednesday, March 7, 2007 3:42PM - 4:18PM |
S4.00003: Mott-insulator phases of coupled two-component Bose gases Invited Speaker: In recent years, strongly-correlated atomic gases have attracted a rapidly-growing attention, mostly motivated by the impressive developments in the manipulation of atoms in optical lattices. In particular, if cold bosons in lattices occupy just the lowest band of the corresponding band structure, the physics is then described by the Bose-Hubbard model, which presents two different types of ground states, namely a superfluid phase and a gaped incompressible insulator phase known as Mott-insulator, characterized by a commensurate occupation per lattice site. For the case of Bose-Bose mixtures, an even richer physics occurs, and in particular a pair superfluid phase, i.e. a superfluid of boson-boson (or hole-hole) composites [1], can occur. In this work we analyze how the formation of a pair-superfluid may significantly influence the qualitative shape of the boundaries of the Mott-insulator regions. We discuss first that our results are relevant for both binary Boson-Boson mixtures, as well as for the case of dipolar gases placed in two unconnected neighboring one-dimensional wires. By combining strong-coupling-expansion calculations, and one-dimensional numerical results based on Matrix-Product-state techniques, we show that the Mott-boundaries strongly modify their shape, acquiring a marked re-entrant character even for low tunneling, which persists even for two-dimensional systems. Finally, we comment on the consequences that this effect may have in the spatial extension of the Mott-insulator plateaux in experiments with an inhomogeneous harmonic trapping in addition to the lattice potential. [1] A. Kuklov, N. Prokof'ev, and B. Svistunov, Phys. Rev. Lett. 92, 050402 (2004). [Preview Abstract] |
Wednesday, March 7, 2007 4:18PM - 4:54PM |
S4.00004: Prospects for strong localization of matter waves by scattering from atoms in a lattice Invited Speaker: Non-interacting matter waves in a disordered potential may exhibit localized states, that is eigenstates with an energy above the potential and with a square integrable wave-function. This intriguing quantum property, related to the concept of Anderson or strong localization, is not straightforward to observe experimentally as in many systems the situation is made complex by interaction and decoherence effects. Ultracold atoms are very flexible systems, where the parasitic effects may be reduced; they are good candidates to observe strong localization if one is able to produce a strong enough disorder. It has been proposed to realize a controllable disorder for matter waves by randomly trapping atoms of another species at the nodes of an optical lattice, with a filling factor less than unity. For the matter wave the optical lattice is far detuned and is assumed to have a negligible mechanical effect. The matter wave then only sees the trapped species, which, in a regime of negligible tunneling, constitutes a static disordered potential of point-like scatterers [1]. We analyze the possibility to observe three-dimensional strong localization of matter waves with this realization of disorder [2]. We show that, provided one is able to adjust the effective scattering length of a trapped scatterer to a value close to the mean inter-scatterer separation d, one can produce localized states with a localization length as short as d, in practice in the micrometer range. We have obtained the value of the effective scattering length by solving the two-body problem of scattering of a free matter wave on a harmonically trapped atom. We predict confinement induced resonances, with an identified physical origin, that may be used to tune the effective scattering length to the desired value, in combination with an interspecies Feshbach resonance. \newline \newline [1] U. Gavish, Y. Castin, Phys. Rev. Lett. 95, 020401 (2005). \newline [2] P. Massignan, Y. Castin, Phys. Rev. A 74, 013616 (2006). [Preview Abstract] |
Wednesday, March 7, 2007 4:54PM - 5:30PM |
S4.00005: Weak and strong localization of cold bosons in optical speckle potentials Invited Speaker: Cold bosons in optical speckle potentials allow to study quantum transport in various geometries under the influence of disorder and dephasing. We use a diagrammatic Green's function approach to calculate the quantum diffusion constant for cold bosonic matter waves in the single-particle regime in optical speckle potentials. These random potentials display strong correlations that were suspected to reduce quantum coherent effects. Our analytical linear-response theory shows that current experiments should be able to measure weak localization corrections to the classical Boltzmann diffusion constant, even in 2 or 3 dimensions. Moreover, the threshold to the strongly (or Anderson) localized regime is accessible if atoms are cold enough and prepared with a sufficiently small momentum dispersion [R. Kuhn et al., Phys. Rev. Lett. 95, 250403 (2005)]. [Preview Abstract] |
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