Experiments on nonlinear matter wave dynamics

Full text: The realization of weakly interacting degenerate Bose-gases has opened up the way to experimentally investigate the regime, where the interaction between matter waves leads to new phenomena. In this talk we will discuss the nonlinear matter wave dynamics in the presence of a periodic and double-well potential. In the first part of the talk we will concentrate on the propagation of interacting matter waves in periodic potentials. We will discuss in detail the formation of localized i.e. non-spreading wave packets, although the atom-atom interaction is repulsive. For a weak periodic potential the first realization of atomic gap solitons will be presented. This can be achieved by realizing the Bose-Einstein condensate of repulsively interacting rubidium atoms in the regime of an effective negative mass, where repulsive interaction leads to a compression of the wave packet. In the regime of deep periodic potentials i.e. an array of weakly coupled condensates, we have observed for the first time macroscopic quantum self-trapping. In contrast to the gap soliton the localization is due to the modification of the local dynamics between neighboring sites in the presence of interaction. In the second part of the talk we will report on the first realization of a single bosonic Josephson-junction. Experimentally this system is implemented with two weakly coupled Bose-Einstein condensates in a double-well potential. We confirm that the exhibited dynamics is a nonlinear generalization of the familiar Josephson effect. The system of ultra cold atoms allows the direct observation of the tunnelling in situ as well as the evolution of the relative phase between the two sites. (author)