57 research outputs found
Frequencies and Damping rates of a 2D Deformed Trapped Bose gas above the Critical Temperature
We derive the equation of motion for the velocity fluctuations of a 2D
deformed trapped Bose gas above the critical temperature in the hydrodynamical
regime. From this equation, we calculate the eigenfrequencies for a few
low-lying excitation modes. Using the method of averages, we derive a
dispersion relation in a deformed trap that interpolates between the
collisionless and hydrodynamic regimes. We make use of this dispersion relation
to calculate the frequencies and the damping rates for monopole and quadrupole
mode in both the regimes. We also discuss the time evolution of the wave packet
width of a Bose gas in a time dependent as well as time independent trap.Comment: 13 pages, latex fil
Two-dimensional atom trapping in field-induced adiabatic potentials
We show how to create a novel two-dimensional trap for ultracold atoms from a conventional magnetic trap. We achieve this by utilizing rf-induced adiabatic potentials to enhance the trapping potential in one direction. We demonstrate the loading process and discuss the experimental conditions under which it might be possible to prepare a 2D Bose condensate. A scheme for the preparation of coherent matterwave bubbles is also discussed
Bose-Einstein condensation in quasi2D trapped gases
We discuss BEC in (quasi)2D trapped gases and find that well below the
transition temperature the equilibrium state is a true condensate,
whereas at intermediate temperatures one has a quasicondensate
(condensate with fluctuating phase). The mean-field interaction in a quasi2D
gas is sensitive to the frequency of the (tight) confinement in the
"frozen" direction, and one can switch the sign of the interaction by changing
. Variation of can also reduce the rates of inelastic
processes, which opens prospects for tunable BEC in trapped quasi2D gases.Comment: 4 revtex pages, 1 figure, text is revised, figure improve
Dilute Bose gas in two dimensions: Density expansions and the Gross-Pitaevskii equation
A dilute two-dimensional (2D) Bose gas at zero temperature is studied by the
method developed earlier by the authors. Low density expansions are derived for
the chemical potential, ground state energy, kinetic and interaction energies.
The expansion parameter is found to be a dimensionless in-medium scattering
amplitude u obeying the equation 1/u+\ln u=-\ln(na^2\pi)-2\gamma, where na^2
and \gamma are the gas parameter and the Euler constant, respectively. It is
shown that the ground state energy is mostly kinetic in the low density limit;
this result does not depend on a specific form of the pairwise interaction
potential, contrary to 3D case. A new form of 2D Gross-Pitaevskii equation is
proposed within our scheme.Comment: 4 pages, REVTeX, no figure
Cold atom gas at very high densities in an optical surface microtrap
An optical microtrap is realized on a dielectric surface by crossing a
tightly focused laser beam with an horizontal evanescent-wave atom mirror. The
nondissipative trap is loaded with cesium atoms through elastic
collisions from a cold reservoir provided by a large-volume optical surface
trap. With an observed 300-fold local increase of the atomic number density
approaching , unprecedented conditions of cold atoms
close to a surface are realized
Creating a low-dimensional quantum gas using dark states in an inelastic evanescent-wave mirror
We discuss an experimental scheme to create a low-dimensional gas of
ultracold atoms, based on inelastic bouncing on an evanescent-wave mirror.
Close to the turning point of the mirror, the atoms are transferred into an
optical dipole trap. This scheme can compress the phase-space density and can
ultimately yield an optically-driven atom laser. An important issue is the
suppression of photon scattering due to ``cross-talk'' between the mirror
potential and the trapping potential. We propose that for alkali atoms the
photon scattering rate can be suppressed by several orders of magnitude if the
atoms are decoupled from the evanescent-wave light. We discuss how such dark
states can be achieved by making use of circularly-polarized evanescent waves.Comment: 8 pages, 4 figure
Extended parametric resonances in nonlinear Schrodinger systems
We study an example of exact parametric resonance in a extended system ruled
by nonlinear partial differential equations of nonlinear Schr\"odinger type. It
is also conjectured how related models not exactly solvable should behave in
the same way. The results have applicability in recent experiments in
Bose-Einstein condensation and to classical problems in Nonlinear Optics.Comment: 1 figur
Observation of radiation pressure exerted by evanescent waves
We report a direct observation of radiation pressure, exerted on cold
rubidium atoms while bouncing on an evanescent-wave atom mirror. We analyze the
radiation pressure by imaging the motion of the atoms after the bounce. The
number of absorbed photons is measured for laser detunings ranging from {190
MHz} to {1.4 GHz} and for angles from {0.9 mrad} to {24 mrad} above the
critical angle of total internal reflection. Depending on these settings, we
find velocity changes parallel with the mirror surface, ranging from 1 to {18
cm/s}. This corresponds to 2 to 31 photon recoils per atom. These results are
independent of the evanescent-wave optical power.Comment: 6 pages, 4 figure
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