Hannover 2010 – scientific programme

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A: Fachverband Atomphysik

A 6: Ultra-Cold Atoms, Ions and BEC I (with Q)

A 6.2: Talk

Tuesday, March 9, 2010, 14:30–14:45, F 303

Bragg Spectroscopy of Ultracold Bosons in an Optical Lattice — •Ulf Bissbort, Yongqiang Li, and Walter Hofstetter — Institut für Theoretische Physik, Goethe Universität Frankfurt

In recent experiments [1,2] it has become possible to probe an interacting atomic gas of ultracold atoms in an optical lattice using Bragg spectroscopy, allowing energy and momentum to be resolved independently within the same measurement. We simulate these experiments under realistic conditions using the time-dependent bosonic Gutzwiller method, which, in contrast to Gross-Pitaevskii theory, captures depletion effects and becomes exact in both the non-interacting and strongly interacting limit. Furthermore, in contrast to static mean-field theory, it is capable of describing correlated excitations, such as Goldstone modes, and is numerically efficient, allowing simulations for all experimentally feasible time scales. In the limit of weak interactions Bogoliubov theory (including trap effects) is recovered, whereas in the case of strong interactions close to the Mott insulating border, a gapped amplitude mode is found to dominate, which has not yet been observed in experiments.

[1] P. Ernst et al., arXiv:0908.4242 (2009).

[2] D. Clément et al., Phys. Rev. Lett. 102, 155301 (2009).