Berlin 2001 – wissenschaftliches Programm
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A: Atomphysik
A 11: Cooling and Trapping III (joint session A and Q)
A 11.2: Gruppenbericht
Mittwoch, 4. April 2001, 16:15–16:45, H3010
Critical Collisional Opacity in a Bose-Einstein Condensate — •Johannes Schuster1, Andreas Marte1, Sebastian Amtage1, Bernhard Sang1, Gerhard Rempe1, and Herman C. W. Beijerinck2 — 1Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, D-85748 Garching, Germany — 2Physics Department, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
We report on the observation of anomalous losses from a 87Rb condensate with a high column density in the absence of an inelastic scattering resonance. We identify a new loss process that limits the achievable column density of ultracold trapped gases in the off-resonant scattering regime as well as in the vicinity of a Feshbach resonance. It is based on collisional avalanches that are triggered by inelastic collisions between trapped atoms or sometimes even by background gas collisions. In the avalanche a considerable part of the kinetic energy that the particles have gained in the inelastic collision is distributed among the trapped atoms by secondary elastic collisions. In our experiment this results in an 8-fold increase of the initial loss rate with respect to the prediction accounting for known loss mechanisms. We present a detailed model accounting for avalanche-like losses which is in good agreement with the observed anomalous decay of our condensate. Our analysis reveals that the collisional opacity of an ultra-cold and dense gas exhibits a critical value. When the critical opacity is exceeded, losses induced by inelastic collisions are substantially enhanced.