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Q: Quantenoptik und Photonik
Q 53: Fallen und Kühlung II
Q 53.7: Vortrag
Mittwoch, 15. März 2006, 16:30–16:45, HII
Multi-channel collisions of cold metastable calcium atoms — •Dirk Hansen and Andreas Hemmerich — Institut für Laserphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg
We present measurements of elastic and inelastic collision rates of metastable calcium in a miniaturized Ioffe trap. The results are compared to recent theoretical calculations [1] that predict unusually large inelastic rates which even exceed the elastic ones. According to [1], the collisions are determined by partial waves with high angular momenta even at low temperatures. The ensembles in our experiment were prepared between 0.5 mK and 2.5 mK by 1-dim Doppler cooling or by adiabatic adjustment of the trap compression. By disturbing the aspect ratio of the sample and measuring its reequilibration we can deduce the cross-dimensional relaxation parameter. The two-body loss parameter is determined from trap decay measurements. Both types of experiments yield nearly equal values for these parameters between 2 × 10−10 and 5 × 10−10 cm3/s and are slightly above [1]. As a consequence, evaporative cooling in a magnetic trap can be ruled out as an option to reach the quantum degenerate regime. The elastic rates are clearly above the unitarity limit for S-wave scattering and confirm the multi-channel character of the collision.
[1] V. Kokoouline, R. Santra, and C. H. Greene, PRL 90, 253201 (2003)