[Show abstract][Hide abstract] ABSTRACT: Fluctuations of the number of condensed atoms in a finite-size, weakly interacting Bose gas confined in a box potential are investigated for temperatures up to the critical region. The canonical partition functions are evaluated using a recursive scheme for smaller systems, and a saddle-point approximation for larger samples, that allows to treat realistic size systems containing up to $N \sim 10^5$ particles. We point out the importance of particle-number constrain and interactions between out of condensate atoms for the statistics near the critical region. For sufficiently large systems the crossover from the anomalous to normal scaling of the fluctuations is observed. The excitations are described in a self-consistent way within the Bogoliubov-Popov approximation, and the interactions between thermal atoms are described by means of the Hartree-Fock method. Comment: 4 pages, 4 figures; vastly improved version, now includes thermal atom interactions for the condensate statistics
Full-text · Article · Aug 2007 · EPL (Europhysics Letters)
[Show abstract][Hide abstract] ABSTRACT: We propose a method for the detection of ground state quantum phases of spinor gases through a series of two quantum nondemolition measurements performed by sending off-resonant, polarized light pulses through the gas. Signatures of various mean-field as well as strongly correlated phases of F=1 and F=2 spinor gases obtained by detecting quantum fluctuations and mean values of polarization of transmitted light are identified.
[Show abstract][Hide abstract] ABSTRACT: We investigate magnetic properties of Mott-insulating phases of ultracold Bose and Fermi spinor gases in optical lattices. We consider in particular the F=2 Bose gas, and the F=3/2 and F=5/2 Fermi gases. We derive effective spin Hamiltonians for one and two atoms per site and discuss the possibilities of manipulating the magnetic properties of the system using optical Feshbach resonances. We discuss low temperature quantum phases of a 87Rb gas in the F=2 hyperfine state, as well as possible realizations of high spin Fermi gases with either 6Li or 132Cs atoms in the F=3/2 state, and with 173Yb atoms in the F=5/2 state. Comment: 15 pages, 5 figures; a completely new and substantially expanded version with several errors corrected
Full-text · Article · Mar 2006 · New Journal of Physics
[Show abstract][Hide abstract] ABSTRACT: We use the classical fields approximation to study a translational flow of
the condensate with respect to the thermal cloud in a weakly interacting Bose
gas. We study both, subcritical and supercritical relative velocity cases and
analyze in detail a state of stationary flow which is reached in the dynamics.
This state corresponds to the thermal equilibrium, which is characterized by
the relative velocity of the condensate and the thermal cloud. The
superfluidity manifests itself in the existence of many thermal equilibria
varying in (the value of this velocity) the relative velocity between the
condensate and the thermal cloud. We pay a particular attention to excitation
spectra in a phonon as well as in a particle regime. Finally, we introduce a
measure of the amount of the superfluid fraction in a weakly interacting Bose
gas, allowing for the precise distinction between the superfluid and the
condensed fractions in a single and consistent framework.
[Show abstract][Hide abstract] ABSTRACT: Classical fields approximation to cold weakly interacting bosons allows for a unified treatment of condensed and uncondensed parts of the system. Until now, however, the quantitative predictions were limited by a dependence of the results on a grid chosen for numerical implementation of the method. In this paper we propose replacing this unphysical ambiguity by an additional postulate: the temperature of the gas at thermal equilibrium should be the same as that of an ideal Bose gas with the same fraction of condensed atoms. As it turns-out, with this additional assumption, nearly all atoms are within the classical fields, thus the method applies to the whole system.
Full-text · Article · Jun 2004 · Physical Review A