Colloquium on March 9, 2009

Walter Hofstetter
Goethe-Universität Frankfurt, Germany

Disorder and interaction in optical lattices

Remarkable experimental progress has recently allowed the creation of fine-grained optical disorder potentials, where localization effects of ultracold atoms can be clearly observed. Adding an optical lattice gives access to highly tunable quantum many-body systems with disorder.
I will focus on the interplay between disorder and strong correlations from a theoretical perspective. Our approach is based on stochastic/dynamical mean-field theories for bosons and fermions. Specifically, I will discuss the following new results:
1) We have investigated the highly debated Bose glass phase in three spatial dimensions for arbitrary temperatures and predict a direct transition between Mott insulator and superfluid.
2) Spin-ordering of fermions (e.g. ^{40}K) in an optical lattice is of current interest.
We provide a complete phase diagram in the presence of disorder, including an
antiferromagnetic metal.
3) We are now able to treat spinful bosons with strong correlations in a unified
dynamical mean-field framework. For 2-component bosons (e.g. ^{41}K - ^{87}Rb) mixtures)
this yields a rich phase diagram, including anisotropic spin order and supersolid phases.