430 research outputs found
Enhanced heat flow in the hydrodynamic-collisionless regime
We study the heat conduction of a cold, thermal cloud in a highly asymmetric
trap. The cloud is axially hydrodynamic, but due to the asymmetric trap
radially collisionless. By locally heating the cloud we excite a thermal dipole
mode and measure its oscillation frequency and damping rate. We find an
unexpectedly large heat conduction compared to the homogeneous case. The
enhanced heat conduction in this regime is partially caused by atoms with a
high angular momentum spiraling in trajectories around the core of the cloud.
Since atoms in these trajectories are almost collisionless they strongly
contribute to the heat transfer. We observe a second, oscillating hydrodynamic
mode, which we identify as a standing wave sound mode.Comment: Sumitted to Phys. Rev. Letters, 4 pages, 4 figure
Inelastic light scattering from a Mott insulator
We propose to use Bragg spectroscopy to measure the excitation spectrum of
the Mott insulator state of an atomic Bose gas in an optical lattice. We
calculate the structure factor of the Mott insulator taking into account both
the selfenergy corrections of the atoms and the corresponding dressing of the
atom-photon interaction. We determine the scattering rate of photons in the
stimulated Raman transition and show that by measuring this scattering rate in
an experiment, in particular the excitation gap of the Mott insulator can be
determined.Comment: 4 pages, 7 figures, LaTeX, submitted to PR
Reaching the hydrodynamic regime in a Bose-Einstein condensate by suppression of avalanche
We report the realization of a Bose-Einstein condensate (BEC) in the
hydrodynamic regime. The hydrodynamic regime is reached by evaporative cooling
at a relative low density suppressing the effect of avalanches. With the
suppression of avalanches a BEC containing 120.10^6 atoms is produced. The
collisional opacity can be tuned from the collisionless regime to a collisional
opacity of more than 3 by compressing the trap after condensation. In the
collisional opaque regime a significant heating of the cloud at time scales
shorter than half of the radial trap period is measured. This is direct proof
that the BEC is hydrodynamic.Comment: Article submitted for Phys. Rev. Letters, 6 figure
Long-range predissociation in two-color photoassociation of ultracold Na atoms
We report two-color photo-associative ionization of sodium
in a Magneto-Optical Trap. The experimental results yield
information on both singly and doubly excited states. We
find that the highest bound vibrational levels (v > 20) of
the singly-excited 0^- g state predissociate into the 3²P3/2 +
3^²S½(Fg=1) dissociation continuum due to avoided cross-
ings of the hyperfine components of this potential with other
molecular symmetries. Based on symmetry and energy con-
siderations we argue that a doubly-excited 1u state remains
autoionizing even when excited only a few GHz above the dis-
sociation continuum
Sideband generation using a Fiber-Optical Modulator (FOM)
We have constructed a Fiber Optical Modulator (FOM),
which produces on the incoming laser frequency shifts of the
order of 30 GHz. The modulator consist of a fiber of suffi-
cient length, where the transmission is saturated by stimulated
Brillouin scattering (SBS). The frequency shift is determined
by the parameters of the fiber and is fixed. The
ratio of intensity of the shifted frequency and the incoming
frequency can be varied over a large range by varying the incoming
intensity with respect to the threshold intensity for
SBS
Imaging trapped quantum gases by off-axis holography
We present a dispersive imaging method for trapped quantum gases based on
digital off-axis holography. Both phase delay and intensity of the probe field
are determined from the same image. Due to the heterodyne gain inherent to the
holographic method it is possible to retrieve the phase delay induced by the
atoms at probe beam doses two orders of magnitude lower than phase-contrast
imaging methods. Using the full field of the probe beam we numerically correct
for image defocusing.Comment: 4 pages, 5 figure
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