60 research outputs found
An optical lattice on an atom chip
Optical dipole traps and atom chips are two very powerful tools for the
quantum manipulation of neutral atoms. We demonstrate that both methods can be
combined by creating an optical lattice potential on an atom chip. A
red-detuned laser beam is retro-reflected using the atom chip surface as a
high-quality mirror, generating a vertical array of purely optical oblate
traps. We load thermal atoms from the chip into the lattice and observe cooling
into the two-dimensional regime where the thermal energy is smaller than a
quantum of transverse excitation. Using a chip-generated Bose-Einstein
condensate, we demonstrate coherent Bloch oscillations in the lattice.Comment: 3 pages, 2 figure
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
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
Multi Mode Interferometer for Guided Matter Waves
We describe the fundamental features of an interferometer for guided matter
waves based on Y-beam splitters and show that, in a quasi two-dimensional
regime, such a device exhibits high contrast fringes even in a multi mode
regime and fed from a thermal source.Comment: Final version (accepted to PRL
Free expansion of two-dimensional condensates with a vortex
We study the free expansion of a pancake-shaped Bose-condensed gas, which is
initially trapped under harmonic confinement and containing a vortex at its
centre. In the case of a radial expansion holding fixed the axial confinement
we consider various models for the interactions, depending on the thickness of
the condensate relative to the value of the scattering length. We are thus able
to evaluate different scattering regimes ranging from quasi-three-dimensional
(Q3D) to strictly two-dimensional (2D). We find that as the system goes from
Q3D to 2D the expansion rate of the condensate increases whereas that of the
vortex core decreases. In the Q3D scattering regime we also examine a fully
free expansion in 3D and find oscillatory behaviour for the vortex core radius:
an initial fast expansion of the vortex core is followed by a slowing down.
Such a nonuniform expansion rate of the vortex core may be taken into account
in designing new experiments.Comment: 10 pages, 4 figure
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
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
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
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