Darmstadt 2008 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 32: Quantengase (Gitter III)

Q 32.4: Talk

Thursday, March 13, 2008, 09:15–09:30, 1C

Controlling interaction-induced dephasing of Bloch oscillations — •Elmar Haller, Mattias Gustavsson, Manfred Mark, Johann Danzl, Gabriel Rojas-Kopeinig, and Hanns-Christoph Nägerl — Institut für Experimentalphysik, Universität Innsbruck, Austria

A BEC in an optical lattice undergoes Bloch oscillations when subject to an external force. However, interactions lead to dephasing, limiting the number of oscillations one can observe.

By tuning the interaction strength using a Feshbach resonance, we quantitatively characterize the dephasing and compare with numerical simulations. The zero crossing of the scattering length can be precisely determined by minimizing dephasing. In the weakly interacting limit, we observe more than 20000 oscillations over 12 s.

For non-zero interaction strength, we find that the momentum distribution of a dephased condensate develops structure on a scale much smaller than the Bloch momentum. This structure becomes visible when the interaction is quickly switched off during release from the lattice and the time-of-flight detection is aided by magnetic levitation to allow for long expansion times.