991 research outputs found
Finite temperature excitations of a trapped Bose gas
We present a detailed study of the temperature dependence of the condensate
and noncondensate density profiles of a Bose-condensed gas in a parabolic trap.
These quantitites are calculated self-consistently using the
Hartree-Fock-Bogoliubov equations within the Popov approximation. Below the
Bose-Einstein transition the excitation frequencies have a realtively weak
temperature dependence even though the condensate is strongly depleted. As the
condensate density goes to zero through the transition, the excitation
frequencies are strongly affected and approach the frequencies of a
noninteracting gas in the high temperature limit.Comment: 4 pages, Latex, 4 postscript figures. Submitted to Physical Review
Letter
Excitation spectrum in a cylindrical Bose-Einstein gas
Whole excitation spectrum is calculated within the Popov approximation of the
Bogoliubov theory for a cylindrical symmetric Bose-Einstein gas trapped
radially by a harmonic potential. The full dispersion relation and its
temperature dependence of the zero sound mode propagating along the axial
direction are evaluated in a self-consistent manner. The sound velocity is
shown to depend not only on the peak density, but also on the axial area
density. Recent sound velocity experiment on Na atom gas is discussed in light
of the present theory.Comment: 4 pages, 5 eps figure
Controlling statistical properties of stored light
Statistical properties of outgoing light pulses are studies after they have
been stored in a medium of atoms in the tripod configuration. A generalized
Hong-Ou-Mandel interference, storing of squeezed states and homodyne signal
analysis are discussed in the context of their dependence on the parameters of
the control fields used for light storage and release.Comment: 5 figure
Implicit and explicit stigma towards mental health treatment
In order to better understand stigma associated with mental health treatment, 118 Clemson University students completed Implicit Association Tasks (IAT) and self-report surveys. The IAT presented terms associated with either medical or psychological treatments or patients, paired with additional positive or negative terms (e.g., good vs. bad). Survey items assessed attitudes towards mental health and medical treatment, as well as mental health and medical patients. Responses from the IAT and survey were compared regarding mental health versus medical treatments and mental health versus medical patients. The IAT results revealed a significant negative implicit bias toward mental health treatment and mental health patients. Explicit survey measures also showed more negative responses toward mental health treatment and patients. Our findings provide both implicit and explicit evidence of stigma associated with mental health treatment and patients. Through better understanding these biases, researchers can work to reduce the stigma associated with mental health treatment
Linear density response in the random phase approximation for confined Bose vapours at finite temperature
A linear response framework is set up for the evaluation of collective
excitations in a confined vapour of interacting Bose atoms at finite
temperature. Focusing on the currently relevant case of contact interactions
between the atoms, the theory is developed within a random phase approximation
with exchange. This approach is naturally introduced in a two-fluid description
by expressing the density response of both the condensate and the
non-condensate in terms of the response of a Hartree-Fock reference gas to the
selfconsistent Hartree-Fock potentials. Such an approximate account of
correlations (i) preserves an interplay between the condensate and the
non-condensate through off-diagonal components of the response, which instead
vanish in the Hartree-Fock-Bogolubov approximation; and (ii) yields a common
resonant structure for the four partial response functions. The theory reduces
to the temperature-dependent Hartree-Fock-Bogolubov-Popov approximation for the
fluctuations of the condensate when its coupling with the density fluctuations
of the non-condensate is neglected. Analytic results are presented which are
amenable to numerical calculations and to inclusion of damping rates.Comment: 14 pages. To appear on J. Phys. : Condens. Matte
Bogoliubov sound speed in periodically modulated Bose-Einstein condensates
We study the Bogoliubov excitations of a Bose-condensed gas in an optical
lattice. Of primary interest is the long wavelength phonon dispersion for both
current-free and current-carrying condensates. We obtain the dispersion
relation by carrying out a systematic expansion of the Bogoliubov equations in
powers of the phonon wave vector. Our result for the current-carrying case
agrees with the one recently obtained by means of a hydrodynamic theory.Comment: 16 pages, no figure
Cross-Phase Modulation and Population Redistribution in a Periodic Tripod Medium
The cross-Kerr effect is studied for two pulses propagating in an atomic
medium in a tripod configuration, dressed by a strong standing wave coupling
beam. Nonlinear phase shifts for both transmitted and reflected beams are
calculated taking into account the redistribution of the population among the
atomic levels which allows one to study the phase shifts in a wide range of
pulse detunings. The influence of other parameters, e.g., the intensity of the
control field and the relaxation rates, on the cross-Kerr effect is also
examined in detail.Comment: 6 figure
Vortex Lattice Structures of a Bose-Einstein Condensate in a Rotating Lattice Potential
We study vortex lattice structures of a trapped Bose-Einstein condensate in a
rotating lattice potential by numerically solving the time-dependent
Gross-Pitaevskii equation. By rotating the lattice potential, we observe the
transition from the Abrikosov vortex lattice to the pinned lattice. We
investigate the transition of the vortex lattice structure by changing
conditions such as angular velocity, intensity, and lattice constant of the
rotating lattice potential.Comment: 6 pages, 8 figures, submitted to Quantum Fluids and Solids Conference
(QFS 2006
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