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