222 research outputs found
Soliton response to transient trap variations
The response of bright and dark solitons to rapid variations in an expulsive
longitudinal trap is investigated. We concentrate on the effect of transient
changes in the trap frequency in the form of temporal delta kicks and the
hyperbolic cotangent functions. Exact expressions are obtained for the soliton
profiles. This is accomplished using the fact that a suitable linear
Schrodinger stationary state solution in time can be effectively combined with
the solutions of non-linear Schrodinger equation, for obtaining solutions of
the Gross-Pitaevskii equation with time dependent scattering length in a
harmonic trap. Interestingly, there is rapid pulse amplification in certain
scenarios
Mermin-Ho vortex in ferromagnetic spinor Bose-Einstein condensates
The Mermin-Ho and Anderson-Toulouse coreless non-singular vortices are
demonstrated to be thermodynamically stable in ferromagnetic spinor
Bose-Einstein condensates with the hyperfine state F=1. The phase diagram is
established in a plane of the rotation drive vs the total magnetization by
comparing the energies for other competing non-axis-symmetric or singular
vortices. Their stability is also checked by evaluating collective modes.Comment: 4 pages, 4 figure
Bose-Einstein condensates with attractive interactions on a ring
Considering an effectively attractive quasi-one-dimensional Bose-Einstein
condensate of atoms confined in a toroidal trap, we find that the system
undergoes a phase transition from a uniform to a localized state, as the
magnitude of the coupling constant increases. Both the mean-field
approximation, as well as a diagonalization scheme are used to attack the
problem.Comment: 4 pages, 4 ps figures, RevTex, typographic errors correcte
Dimensional and Temperature Crossover in Trapped Bose Gases
We investigate the long-range phase coherence of homogeneous and trapped Bose
gases as a function of the geometry of the trap, the temperature, and the
mean-field interactions in the weakly interacting limit. We explicitly take
into account the (quasi)condensate depletion due to quantum and thermal
fluctuations, i.e., we include the effects of both phase and density
fluctuations. In particular, we determine the phase diagram of the gas by
calculating the off-diagonal one-particle density matrix and discuss the
various crossovers that occur in this phase diagram and the feasibility of
their experimental observation in trapped Bose gases.Comment: One figure added, typos corrected, refernces adde
Effectively attractive Bose-Einstein condensates in a rotating toroidal trap
We examine an effectively attractive quasi-one-dimensional Bose-Einstein
condensate of atoms confined in a rotating toroidal trap, as the magnitude of
the coupling constant and the rotational frequency are varied. Using both a
variational mean-field approach, as well as a diagonalization technique, we
identify the phase diagram between a uniform and a localized state and we
describe the system in the two phases.Comment: 4 pages, 4 ps figures, RevTe
In-situ velocity imaging of ultracold atoms using slow--light
The optical response of a moving medium suitably driven into a slow-light
propagation regime strongly depends on its velocity. This effect can be used to
devise a novel scheme for imaging ultraslow velocity fields. The scheme turns
out to be particularly amenable to study in-situ the dynamics of collective and
topological excitations of a trapped Bose-Einstein condensate. We illustrate
the advantages of using slow-light imaging specifically for sloshing
oscillations and bent vortices in a stirred condensate
Kinetic Theory of Collective Excitations and Damping in Bose-Einstein Condensed Gases
We calculate the frequencies and damping rates of the low-lying collective
modes of a Bose-Einstein condensed gas at nonzero temperature. We use a complex
nonlinear Schr\"odinger equation to determine the dynamics of the condensate
atoms, and couple it to a Boltzmann equation for the noncondensate atoms. In
this manner we take into account both collisions between
noncondensate-noncondensate and condensate-noncondensate atoms. We solve the
linear response of these equations, using a time-dependent gaussian trial
function for the condensate wave function and a truncated power expansion for
the deviation function of the thermal cloud. As a result, our calculation turns
out to be characterized by two dimensionless parameters proportional to the
noncondensate-noncondensate and condensate-noncondensate mean collision times.
We find in general quite good agreement with experiment, both for the
frequencies and damping of the collective modes.Comment: 10 pages, 8 figure
't Hooft-Polyakov Monopoles in an Antiferromagnetic Bose-Einstein Condensate
We show that an antiferromagnetic spin-1 Bose-Einstein condensate, which can
for instance be created with Na-23 atoms in an optical trap, has not only
singular line-like vortex excitations, but also allows for singular point-like
topological excitations, i.e., 't Hooft-Polyakov monopoles. We discuss the
static and dynamic properties ofthese monopoles.Comment: Four pages of ReVTeX and 1 postscript figur
Extension of Bogoliubov theory to quasi-condensates
We present an extension of the well-known Bogoliubov theory to treat low
dimensional degenerate Bose gases in the limit of weak interactions and low
density fluctuations. We use a density-phase representation and show that a
precise definition of the phase operator requires a space discretisation in
cells of size . We perform a systematic expansion of the Hamiltonian in
terms of two small parameters, the relative density fluctuations inside a cell
and the phase change over a cell. The resulting macroscopic observables can be
computed in one, two and three dimensions with no ultraviolet or infrared
divergence. Furthermore this approach exactly matches Bogoliubov's approach
when there is a true condensate. We give the resulting expressions for the
equation of state of the gas, the ground state energy, the first order and
second order correlations functions of the field. Explicit calculations are
done for homogeneous systems.Comment: 32 pages, 2 figures; typos corrected in revised versio
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