ANDERSON LOCALIZATION OF A NON-INTERACTING BOSE-EINSTEIN CONDENSATE
One of the most intriguing phenomena in physics is the localization of waves in disordered media. This phenomenon was originally predicted by P. W. Anderson, fifty years ago, in the context of transport of electrons in crystals, but it has never been directly observed for matter waves. Ultracold atoms open a new scenario for the study of disorder-induced localization, due to the high degree of control of most of the system parameters, including interactions. For the first time we have employed a noninteracting Bose-Einstein condensate to study Anderson localization. The experiment is performed in a 1D lattice with quasi-periodic disorder, a system which features a crossover between extended and exponentially localized states as in the case of purely random disorder in higher dimensions. We clearly demonstrate localization by investigating transport properties, spatial and momentum distributions. Since the interaction in the condensate can be controlled, this system represents a novel tool to solve fundamental questions on the interplay of disorder and interactions and to explore exotic quantum phases.
