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Q: Quantenoptik und Photonik

Q 14: Quantengase III

Q 14.6: Vortrag

Montag, 13. März 2006, 18:15–18:30, HVI

Formation of long-range order in a growing Bose-Einstein condensate — •Stephan Ritter, Anton Öttl, Tobias Donner, Thomas Bourdel, Michael Köhl, and Tilman Esslinger — Institut für Quantenelektronik, ETH Zürich, CH-8093 Zürich, Schweiz

We have experimentally investigated the temporal evolution of long-range order in an ultracold gas of atoms during the formation of a Bose-Einstein condensate (BEC). The growth of a quantum degenerate gas from a thermal vapor is associated with a sharp increase in the peak density of the cloud. Here we investigate how in this process the phase coherence, a characteristic feature of the equilibrium BEC, develops in time. We probe the coherence between two regions of an atomic cloud by continuously output coupling atoms from the two regions simultaneously. The two atomic beams show an interference pattern with a contrast given by the phase coherence between the two output coupling regions. We observe the matter wave interference pattern using a high-finesse optical cavity which serves as a single-atom detector with high quantum efficiency. Therefore, only very few atoms need to be output coupled from the atomic cloud and the coherence of two regions can be monitored without perturbing the formation process.

During the formation, we measure the coherence of two regions of the cloud with variable separation in real-time and simultaneously probe their density. The experimental results of these measurements will be presented.