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Q: Fachverband Quantenoptik und Photonik

Q 42: Quantum gases: Disorder- or interaction-induced effects

Q 42.1: Gruppenbericht

Donnerstag, 20. März 2014, 14:00–14:30, UDL HS2002

Perturbative and Non-Perturbative Methods for Tackling the Dirty Boson Problem — •Axel Pelster — Fachbereich Physik und Forschungszentrum OPTIMAS, Technische Universität Kaiserslautern, Germany

The notoriously difficult dirty boson problem amounts to understanding the emergence of coherence and order for ultracold bosonic atoms in the presence of a quenched disorder potential. It appears either naturally like in current carrying wire traps, or artificially like in laser speckle fields. Theoretically it is intriguing because of the competition of localization and interaction as well as of disorder and superfluidity.

We start with solving perturbatively the coupled hydrodynamic equations for a homogeneous BEC with a weak disorder potential. In this way we reproduce the explicit expressions of Huang and Meng for the disorder corrections of both condensate and superfluid density. In addition, we consider a 1d ring trap and determine how the superfluid velocity depends on the disorder correlation length.

Afterwards, we compare two non-perturbative methods, where the first one is based on a Hartree-Fock mean-field theory by invoking replica symmetry and the second one follows from a Gaussian approximation for correlation functions. For a homogeneous BEC we find for strong disorder a quantum phase transition from a superfluid to a Bose-glass phase whose order changes from second to first order for increasing disorder correlation length. Furthermore, we determine for a harmonically trapped BEC the respective density profiles of both the global condensate and the fragmented BECs for Lorentzian disorder.