Several years ago Carl Wieman's group studied the effect of suddenly changing the nature of the interatomic interactions in a Bose-Einstein condensate (BEC) from repulsive to attractive. The researchers observed the collapse, or implosion, of the BEC which has since been known as a "bosenova." A burst of hot atoms was ejected from the BEC, leaving a remnant BEC behind. An outstanding mystery regarding the observations was that the number of atoms in the remnant BEC often exceeded the value predicted by a basic theory that worked well to explain other observed effects. Recently, the group discovered the fascinating answer to this puzzle. Upon closer inspection, researchers observed that during the collapse process, the atoms in the remnant BEC remarkably organize themselves into bright matter-wave solitons. The number of atoms contained in each soliton never exceeds the critical number predicted by theory. The solitons form with relative phases such that they repel each other, oscillating back and forth in the magnetic confining potential for many seconds. The group observed that, depending on the collapse conditions, up to six solitons can form simultaneously. The figure shows standard absorption images of these solitons as well as the cross sections of the images.—Sarah Thompson

Reference:
S. L. Cornish, S. T. Thompson, and C. E. Wieman, Formation of bright matter-wave solitons during the collapse of attractive Bose-Einstein condensates, Physical Review Letters, 96 170401 (2006).

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