Formation of Bright Matter-Wave Solitons during the Collapse of Attractive Bose-Einstein Condensates

We observe bright matter-wave solitons form during the collapse of 85 Rb condensates in a three-dimensional (3D) magnetic trap 1 . The collapse is induced by using a Feshbach resonance to suddenly switch the atomic interactions from repulsive to attractive 2 . Our previous observations of the collapse process 3 revealed that remnant condensates containing several times the critical number of atoms for the onset of instability survive the collapse. It was not understood why such condensates did not undergo further collapse until the number of atoms remaining was below the critical number. In the work presented here, we explain this result by showing that the remnant condensate forms a highly robust configuration of 3D solitons, such that each soliton satisfies the condition for stability. The solitons are observed to oscillate along the (weaker) axial direction of the trap, colliding repeatedly in the trap centre. The stability of this motion out to long observation times indicates that neighboring solitons have a relative phase that ensures that they interact repulsively even though the atomic interactions are attractive 4 .