# Stuttgart 2012 – wissenschaftliches Programm

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# Q: Fachverband Quantenoptik und Photonik

## Q 22: Quantengase: Wechselwirkungseffekte 1

### Q 22.1: Gruppenbericht

### Dienstag, 13. März 2012, 10:30–11:00, V7.03

**Dipolar Bose-Einstein Condensates with Weak Disorder** — •Axel Pelster — Hanse-Wissenschaftskolleg, Delmenhorst, Germany

Recent progress nourishes the prospects of future experiments which investigate Bose-Einstein condensates (BECs) with
a strong anisotropic and long-range dipole-dipole interaction. Against this background we
solve semiclassicaly the Bogoliubov-de Gennes theory for harmonically trapped dipolar
BECs which is justified in the thermodynamic limit [1]. In this way we predict for various static and dynamic observables
quantum fluctuations, which go beyond the so far experimentally established mean-field theory.

Furthermore, we report on recent progress in understanding the properties
of ultracold bosonic atoms in potentials with quenched disorder [2].
This notoriously difficult *dirty boson problem* is experimentally relevant for the miniaturization of
BECs on
chips and can also be studied by tailoring disorder potentials via laser
speckle fields. Theoretically it is intriguing because of the competition
of localization and interaction as well as of disorder and superfluidity.

Finally, we combine both previous topics and consider the impact of weak disorder upon a polarized
homogeneous dipolar BEC.
We find that both disorder [3] and thermal fluctuations lead to anisotropic superfluidity which can only be described
by a corresponding extension of the standard hydrodynamic Landau-Khalatnikov (LK) theory. A linearization of the modified
LK equations yields for first and second sound a characteristic direction dependence which should be detectable with
Bragg spectroscopy.

[1] A.R.P. Lima and A. Pelster, Phys. Rev. A **84**, 041604(R) (2011) and `arXiv:1111.0900`.

[2] R. Graham and A. Pelster, Int. J. Bif. Chaos **19**, 2745 (2009).

[3] C. Krumnow and A. Pelster, Phys. Rev. A **84**, 021608(R) (2011).