Thermally induced coherence in a Mott insulator of bosonic atoms

Naively, one may think 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.