2,360 research outputs found

    Quantum kinetic theory of trapped atomic gases

    Full text link
    We present a general framework in which we can accurately describe the non-equilibrium dynamics of trapped atomic gases. This is achieved by deriving a single Fokker-Planck equation for the gas. In this way we are able to discuss not only the dynamics of an interacting gas above and below the critical temperature at which the gas becomes superfluid, but also during the phase transition itself. The last topic cannot be studied on the basis of the usual mean-field theory and was the main motivation for our work. To show, however, that the Fokker-Planck equation is not only of interest for recent experiments on the dynamics of Bose-Einstein condensation, we also indicate how it can, for instance, be applied to the study of the collective modes of a condensed Bose gas.Comment: 12 pages of LaTeX and two postscript figures. Contribution to NATO-ASI Dynamics: Models and Kinetic Methods for Non-Equilibrium Many-Body Systems edited by John Karkhec

    Coherent versus Incoherent Dynamics during Bose-Einstein Condensation in Atomic Gases

    Full text link
    We review and extend the theory of the dynamics of Bose-Einstein condensation in weakly interacting atomic gases. We present in a unified way both the semiclassical theory as well as the full quantum theory. This is achieved by deriving a Fokker-Planck equation that incorporates both the coherent and incoherent effects of the interactions in a dilute Bose gas. In first instance we focus our attention on the nonequilibrium dynamics of a homogeneous Bose gas with a positive interatomic scattering length. After that we discuss how our results can be generalized to the inhomogeneous situation that exists in the present experiments with magnetically trapped alkali gases, and how we can deal with a negative interatomic scattering length in that case as well. We also show how to arrive at a discription of the collective modes of the gas that obeys the Kohn theorem at all temperatures. The theory is based on the many-body T-matrix approximation throughout, since this approximation has the correct physical behavior near the critical temperature and also treats the coherent and incoherent processes taking place in the gas on an equal footing.Comment: In response to referee report I have rewritten the introduction. I have also added new results for the decay rate of a condensate with negative scattering length and for the collisionless collective modes of a Bose condensed atomic gas at nonzero temperature

    Screening of Coulomb interactions in Holography

    Full text link
    We introduce Coulomb interactions in the holographic description of strongly interacting systems, by performing a (current-current) double-trace deformation of the boundary theory. In the theory dual to a Reissner-Nordstr\"om background, this deformation leads to gapped plasmon modes in the density-density response, as expected from conventional RPA calculations. We further show that by introducing a (d+1)(d + 1)-dimensional Coulomb interaction in a boundary theory in dd spacetime dimensions, we recover plasmon modes whose dispersion is proportional to ∣k∣\sqrt{|\mathbf{k}|}, as observed for example in graphene layers. Moreover, motivated by recent experimental results in layered cuprate high-temperature superconductors, we present a toy model for a layered system consisting of an infinite stack of (spatially) two-dimensional layers, that are coupled only by the long-range Coulomb interaction. This leads to low-energy `acoustic plasmons'. Finally, we compute the optical conductivity of the deformed theory in d=3+1d = 3 + 1, where a logarithmic correction is present and we show how this can be related to the conductivity measured in Dirac and Weyl semimetals.Comment: 39 pages, 15 figures; Published version (small changes according to referee's suggestions

    Condensed matter physics with trapped atomic Fermi gases

    Full text link
    We present an overview of the various phase transitions that we anticipate to occur in trapped fermionic alkali gases. We also discuss the prospects of observing these transitions in (doubly) spin-polarized Li-6 and K-40 gases, which are now actively being studied by various experimental groups around the world.Comment: 18 pages of LaTeX and 2 postscript figures. Contribution to the international summer school `Enrico Fermi' on Bose-Einstein condensation in atomic gases, Varenna 199

    Sweeping a molecular Bose-Einstein condensate across a Feshbach resonance

    Full text link
    We consider the dissociation of a molecular Bose-Einstein condensate during a magnetic-field sweep through a Feshbach resonance that starts on the molecular side of the resonance and ends on the atomic side. In particular, we determine the energy distribution of the atoms produced after the sweep. We find that the shape of the energy distribution strongly depends on the rate of the magnetic-field sweep, in a manner that is in good agreement with recent experiments.Comment: 4.2 pages, 4 figure
    • …
    corecore