Thermally induced coherence in a Mott insulator of bosonic atoms

Conventional wisdom is that increasing temperature causes quantum coherence to decrease. Using finite temperature perturbation theory and exact calculations for the strongly correlated bosonic Mott insulating state we show a practical counter-example that can be explored in optical lattice experiments: the short-range coherence of the Mott insulating phase can increase substantially with increasing temperature. We demonstrate that this phenomenon originates from thermally produced defects that can tunnel with ease. Since the near zero temperature coherence properties have been measured with high precision we expect these results to be verifiable in current experiments.Comment: 5 pages, 3 figure

Spatially selective Bragg scattering: a signature for vortices in Bose-Einstein condensates

We demonstrate that Bragg scattering from a condensate can be sensitive to the spatial phase distribution of the initial state. This allows preferential scattering from a selected spatial region, and provides a robust signature for a vortex state. We develop an analytic model which accurately describes this phenomenon and we give quantitative predictions for current experimental conditions.Comment: 5 pages, 3 figure