Bright Bose-Einstein Gap Solitons of Atoms with Repulsive Interaction

We report on the first experimental observation of bright matter wave solitons for ${}^{87}\mathrm{Rb}$ atoms with repulsive atom-atom interaction. This counterintuitive situation arises inside a weak periodic potential, where anomalous dispersion can be realized at the Brillouin zone boundary. If the coherent atomic wave packet is prepared at the corresponding band edge, a bright soliton is formed inside the gap. The strength of our system is the precise control of preparation and real time manipulation, allowing the systematic investigation of gap solitons.