Berlin 2012 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 30: Matter At Low Temperature: Quantum Liquids, Bose-Einstein Condensates, Ultra-cold Atoms, ... 1

TT 30.4: Vortrag

Mittwoch, 28. März 2012, 16:00–16:15, H 3005

Constant forces induce negative absolute temperatures in optical lattices — •Stephan Mandt¹, Akos Rapp², and Achim Rosch¹ — ¹Institute for Theoretical Physics, University of Cologne, Germany — ²Institute for Theoretical Physics, University of Hanover, Germany

Ultracold atoms in optical lattices offer a novel possibility to explore transport properties of model Hamiltonians, such as the Hubbard model for Fermions, in absence of impurities, lattice defects or phonons. The fact that the Hubbard model describes a thermally isolated system has got severe consequences on its transport properties: a cloud of interacting fermionic atoms in an optical lattice in presence of a gravitational potential, e.g., doesn’t simply "fall downwards". Instead, we show that it diffuses symmetrically upwards and downwards, while its radius grows subdiffusively in time according to R ∝ t^1/3. We also show that negative absolute temperatures naturally emerge in such a situation, and how equilibrated negative temperatures can be realized in optical lattices.