# Berlin 2014 – wissenschaftliches Programm

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# Q: Fachverband Quantenoptik und Photonik

## Q 32: Poster: Quantum gases, ultracold atoms and molecules

### Q 32.54: Poster

### Mittwoch, 19. März 2014, 16:30–18:30, Spree-Palais

**Bose-Einstein Condensates with Strong Disorder – Gaussian Approximation for Correlation Functions** — •Branko Nikolić^{1}, Antun Balaž^{2}, and Axel Pelster^{3} — ^{1}Department of Physics, Freie Universität Berlin, Germany — ^{2}Scientific Computing Laboratory, Institute of Physics Belgrade, University of Belgrade, Serbia — ^{3}Fachbereich Physik und Forschungszentrum OPTIMAS, Technische Universität Kaiserslautern, Germany

Ultracold bosonic atoms in potentials with quenched disorder represent a notoriously difficult problem due to the competition of localization and superfluidity. Whereas some initial promising results are known for weak disorder within a Bogoliubov theory of dirty bosons [1], the case of strong disorder is still quite elusive [2]. Here we work out a non-perturbative approach towards the dirty boson problem at zero temperature which is based on a Gaussian approximation for correlation functions of the disorder potential and the condensate wave function solving the Gross-Pitaevskii equation. For contact interaction we find that the case of delta-correlated disorder can be treated analytically, whereas the case of a Lorentzian disorder correlation necessitates a numerical solution of a set of self-consistency equations. For weak disorder we reproduce the condensate depletion of Huang and Meng and for strong disorder we yield a quantum phase transition to a Bose-glass phase.

[1] K. Huang, H.-F. Meng,
Phys. Rev. Lett. **69**, 644 (1992)

[2] P. Navez, A. Pelster, and R. Graham,
Appl. Phys. B **86**, 395 (2007)