Heidelberg 2015 – wissenschaftliches Programm

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A: Fachverband Atomphysik

A 4: Ultra-cold atoms, ions and BEC I (with Q)

A 4.5: Vortrag

Montag, 23. März 2015, 15:30–15:45, C/HSW

Anomalously long-range coherence in one dimensional Bose gases far from equilibrium — •Alexander Schnell1,2, Daniel Vorberg1, Roland Ketzmerick1,2, and André Eckardt11Max-Planck-Institut für Physik komplexer Systeme, Dresden — 2Institut für Theoretische Physik, Technische Universität Dresden

As a consequence of the Mermin-Wagner theorem, a one-dimensional Bose gas in equilibrium at finite temperature does not feature Bose condensation in the thermodynamic limit (system size to infinity at constant density). The single-particle correlation function decays exponentially on a finite coherence length ℓ. Bose condensation can, however, occur in a system of finite length L, when for sufficiently large densities n or inverse temperatures β the ratio ℓ/L approaches one.

We investigate the situation where a one-dimensional ideal Bose gas of densisty n in contact with a heat bath of finite inverse temperature β is driven into a non-equilibrium steady state (NESS) by coupling it also to a second, population inverted heat bath described by a negative temperature. We find conditions where the NESS features fragmented Bose condensation into three single-particle modes [1]. Remarkably, this form of non-equilibrium condensation occurs up to system sizes L that can be several orders of magnitude larger than those for which equilibrium Bose condensation occurs for the same β and n.

[1] Vorberg et. al., Phys. Rev. Lett. 111, 240405 (2013)

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