Mainz 2017 – wissenschaftliches Programm

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Q: Fachverband Quantenoptik und Photonik

Q 6: Quantum Gases: Bosons I

Q 6.3: Vortrag

Montag, 6. März 2017, 15:00–15:15, P 204

Strongly anomalous non-thermal fixed point in a quenched two-dimensional Bose gas — •Markus Karl^1,2 and Thomas Gasenzer^1,2 — ¹Kirchhoff-Institut für Physik, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 227, 69120 Heidelberg — ²ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstraße 1, 64291 Darmstadt, Germany

Universal scaling behaviour in the relaxation dynamics of an isolated two-dimensional Bose gas is studied by means of semi-classical stochastic simulations of the Gross-Pitaevskii model. The system is quenched far out of equilibrium by imprinting vortex defects into an otherwise phase-coherent condensate. A strongly anomalous non-thermal fixed point is identified, signalled by a universal scaling form for the time-dependent occupation spectrum at late times. The fixed point is associated with a slowed power-law decay of the defects in the case that the dissipative coupling to the thermal background noise is suppressed. Interpreting our results in the context of phase-ordering kinetics and coarsening dynamics, we find numerical evidence for a new type of defect-ordering process far from equilibrium. This process is characterised by a large dynamical critical exponent z=5, implying an anomalously slow algebraic progress of the system towards thermal equilibrium, and is distinctly different from coarsening within known near-equilibrium universality classes.