# Heidelberg 2015 – wissenschaftliches Programm

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# A: Fachverband Atomphysik

## A 31: Ultracold Atoms: Trapping and Cooling I (with Q)

### A 31.4: Vortrag

### Donnerstag, 26. März 2015, 12:00–12:15, P/H2

**Mean-Field Analysis of Selforganization of Atoms in Cavities** — •Simon Jäger, Stefan Schütz, and Giovanna Morigi — Theoretische Physik, Universität des Saarlandes, D-66123 Saarbrücken, Germany

Atoms can spontaneously form spatially ordered structures in optical resonators when they are transversally driven by lasers. This occurs by means of photon-mediated long-range forces, which establish correlations when the intracavity photon number exceeds a threshold value. The selforganization transition is an out-of-equilibrium phenomenon, where losses are an essential element determining the threshold behaviour [1]. In this contribution, we analyse the nature of the transition by means of a mean-field Fokker-Planck equation (FPE), which has been systematically derived from the master equation of atoms and cavity field and describes the dynamics of the one-particle density matrix. This FPE has the form of a Vlaslov equation when retardation effects, giving rise to noise, are neglected [2]. We analyse the dynamics of the order parameter, which quantifies the localization of the atoms in ordered patterns, and show that close to the selforganization threshold its dynamics is determined by a potential of Landau form in an appropriately defined thermodynamic limit. We then perform a stability analysis which permits us to identify the spectral properties of the intracavity field.

[1] S.Schütz and G. Morigi, Phys. Rev. Lett. **113**, 203002 (2014)

[2] A. Campa, T. Dauxois, and S. Ruffo, Phys. Rep. **480**, 57 (2009)