Düsseldorf 2007 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 64: Poster Quantengase

Q 64.14: Poster

Thursday, March 22, 2007, 16:30–18:30, Poster C

Quantum Dynamical vs. Boltzmann description of an equilibrating Ultracold Bose Gas — •Alexander Branschädel and Thomas Gasenzer — Institut für Theoretische Physik, Universität Heidelberg, Philosophenweg 16, 69120 Heidelberg

A dynamical many-body theory is presented which systematically extends beyond mean-field and perturbative quantum-field theoretical procedures. It allows us to study the dynamics of strongly interacting quantum-degenerate atomic gases. The non-perturbative approximation scheme is based on a systematic expansion of the two-particle irreducible effective action in powers of the inverse number of field components. This yields dynamic equations which contain direct scattering, memory and “off-shell” effects that are not captured by the Gross-Pitaevskii equation and go far beyond Quantum Boltzmann type descriptions. We apply the theory to a homogeneous ultracold Bose gas in one spatial dimension. Considering the time evolution of an initial state far from equilibrium we show that it quickly evolves to a non-equilibrium quasistationary state and discuss the possibility to attribute an effective temperature to it. The approach to thermal equilibrium is found to be extremely slow. We compare in detail the predictions of the full quantum dynamical theory to that of a kinetic, i.e. Quantum Boltzmann description of the equilibration.