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A: Atomphysik

A 9: Poster I: Ultrakalte Atome und BEC

A 9.12: Poster

Tuesday, March 14, 2006, 16:30–18:30, Labsaal

Bose-Einstein condensate in a double-well potential at finite temperature — •Börge Hemmerling, Rudolf Gati, Timo Ottenstein, Jerome Esteve, and Markus K. Oberthaler — Kirchhoff-Institut für Physik, Universität Heidelberg, Im Neuenheimer Feld 227, D-69120 Heidelberg

Here we present the experimental implementation of a single bosonic Josephson junction and discuss our latest results on the influence of thermal effects. The bosonic Josephson junction is realized by splitting a Bose-Einstein condensate with a double-well potential into two localized modes and couple them via tunnelling through the barrier. The potential is generated by the superposition of a dipole trap and a standing light wave and thus allows for a high degree of control over the experimental parameters. Especially the height of the barrier leading to different tunnelling couplings can be accessed directly. Additionally, the temperature of the trapped atoms can be varied over a wide range by holding the sample for different times in the trap. With this bosonic Josephson junction we investigate random fluctuations of the relative phase between the localized modes as a function of the coupling strength and the temperature of the thermal background. The quantitative agreement of our results with a classical model allows for the application of the measurements for thermometry. With this new tool it becomes possible to observe the heating up of a Bose-Einstein condensate in a regime where the standard time-of-flight method fails. These experiments reveal that the heat capacity of the degenerate Bose gas is in agreement with the theoretical prediction confirming the third law of thermodynamics.