Tunable interactions in ultracold Bose gases

We have created bright matter wave solitons by using a Feshbach resonance to tune the interactions in a Bose-Einstein condensate of 7Li. The solitons are made to propagate in a one-dimensional potential formed by a focused laser beam. We observed dispersive wave-like properties for repulsive interactions and soliton-like behavior for attractive interactions. Adjacent solitons are observed to interact repulsively.