Regensburg 2013 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 40: Poster Session Correlated Electrons
TT 40.89: Poster
Mittwoch, 13. März 2013, 15:00–19:00, Poster D
Negative absolute temperature for motional degrees of freedom and expansion of interacting bosons in optical lattices — •Simon Braun1,2, Philipp Ronzheimer1,2, Michael Schreiber1,2, Sean Hodgman1,2, Daniel Garbe1,2, Immanuel Bloch1,2, and Ulrich Schneider1,2 — 1Ludwig-Maximilians-Universität München — 2Max-Planck-Institut für Quantenoptik, Garching
Absolute temperature is usually bound to be strictly positive. However, in systems with an upper energy bound, negative absolute temperature states are possible, where the occupation probability of states increases with their energy. We realized a negative absolute temperature state for motional degrees of freedom with ultracold bosonic 39K atoms in an optical lattice, by implementing the attractive Bose-Hubbard Hamiltonian. This new state strikingly revealed itself by strong occupation peaks at maximum kinetic energy. We found that the negative absolute temperature state is close to degeneracy and as stable as the corresponding positive temperature state.
Additionally, we investigated the out-of-equilibrium expansion dynamics of interacting bosons in one- and two-dimensional Hubbard systems. We found that the fastest, ballistic expansions occur in the integrable limits. In 1D, these are both the non-interacting and the strongly interacting limit where the system enters into the hard-core boson regime. For intermediate interactions, the expansion slows down significantly. In 2D, the system expands ballistically only in the non-interacting case, and even small interactions lead to strongly diffusive behavior. We also mapped out the transition between 1D and 2D.