Tuesday, July 30, 2013

1307.7188 (Stephan Mandt et al.)

Relaxation towards negative temperatures in bosonic systems: generalized
Gibbs ensembles and beyond integrability

Stephan Mandt, Adrian E. Feiguin, Salvatore R. Manmana
Motivated by the recent experimental observation of negative absolute temperature states in systems of ultracold atomic gases on optical lattices [Braun et al., Science 339, 52-55 (2013)], we investigate theoretically the formation of these states. More specifically, we consider the relaxation after a sudden inversion of the external parabolic confining potential in the one-dimensional inhomogeneous Bose-Hubbard model. First, we focus on the integrable hard-core boson limit which allows us to treat large systems and arbitrarily long times, providing convincing numerical evidence for relaxation to a generalized Gibbs ensemble at negative temperatures T<0, being defined by us in this context. Second, going beyond one dimension, we demonstrate that the emergence of negative temperature states can be understood in a dual way in terms of positive temperatures, which relies on a dynamic symmetry of the Hubbard model. We complement the study by exact diagonalization simulations at finite values of the on-site interaction.
View original: http://arxiv.org/abs/1307.7188

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