BEC of cesium in an optical surface trap
In the evening of Aug 25th, 2003, our team at the Institute for Experimental Physics at Innsbruck University has created a Bose-Einstein condensate (BEC) of cesium atoms in an optical surface trap. Our experiment is the second to reach condensation of cesium, after its first demonstration on Oct 5th, 2002, in the lab next door. Our trap strongly compresses the atomic cloud in one direction, leading to a two-dimensional condensate!
Instead of using conventional traps in free space, we trap and cool the atoms in close proximity to a glass surface. A repulsive evanescent wave prevents the atoms from hitting the surface, and supports them against gravity at a distance of only a few micrometers. In order to confine the atomic motion also in the two horizontal directions, we focus an attractive laser beam onto the glass surface.
When the intensity of the attractive focused beam is slowly reduced, the hotter atoms escape from the trap, and a colder atomic sample remains after thermalization. Using this technique, we are able to reach extremely low temperatures and high phase-space densities. Under such conditions, the atomic motion can no longer be described classically, and quantum-mechanical effects arise.
After evaporation, the measured values for the temperature, number of atoms (a few thousands) and trap parameters indicate a peak phase-space density clearly higher than one. In order to prove the presence of a condensate, we demonstrate the occurance of a mean-field effect, which is absent in thermal samples. In a condensate, the interaction strength affects the collective behavior of the atoms. In particular, attractive interactions lead to an implosion of the condensate and consequent inelastic loss.
Evidence for Efimov states
A remarkable result in research could be achieved in showing the evidence
for Efimov states. Together with the LevT team it was shown that trapped Cs
atoms with a temperature of below 250 nK experience a giant three-body
recombination loss if they are put into the regime of negative two-body
scattering lenghts ( Nature 440, 315 (2006) cond-mat/0512394).
We are supported by the Austrian Science Fund (Fonds zur Förderung der wissenschaftlichen Forschung, FWF) in the frame of the Spezialforschungsbereich F15 "Control and Measurement of Coherent Quantum Systems" and the FASTnet (Field Atom Surface Training Network, within the 5th Framework Programme of the European Union).
last change: 03-03-09 by BS