# Heidelberg 2015 – wissenschaftliches Programm

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# Q: Fachverband Quantenoptik und Photonik

## Q 15: Poster: Quantum Optics and Photonics I

### Q 15.33: Poster

### Montag, 23. März 2015, 17:00–19:00, C/Foyer

**Quasi-Condensation and Superfluidity in a Ring Trap** — Hansjörg Polster and •Carsten Henkel — University of Potsdam, Germany

Low-dimensional Bose gases suffer from large phase fluctuations that prevent the formation of a proper condensate as defined by Penrose and Onsager. We study a one-dimensional, phase-fluctuating gas in the cross-over region between the ideal gas and the quasi-condensate (weak interactions). Correlation functions of any order are found by mapping the quantum field theory to a random walk in the complex plane, making a classical field approximation [1]. We discuss in particular full distribution functions for the atomic density, including the formation of pairs and clusters at the onset of quasi-condensation. Currently we investigate the distribution function of the total particle current in a rotating ring trap [2] which provides insight into the superfluid behaviour of the gas.

[1] L. W. Gruenberg and L. Gunther,
*Phys. Lett. A* **38** (1972) 463;
D. J. Scalapino, M. Sears, and R. A. Ferrell,
*Phys. Rev. B* **6** (1972) 3409

[2] I. Carusotto and Y. Castin,
*C. R. Physique* **5** (2004) 107