Similar to the common disappearing act by any magician, lithium atoms under ultra-cold conditions can also disappear because of their ability to pass through other particles of matter.

Rice University physicist Randy Hulet and his team have seen the unique behavior of lithium atoms while colliding pairs of Bose Einstein condensates (BECs) that were prepared in special states.

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BECs are clusters of more than 100,000 lithium atoms that are cooled very close to absolute zero. Under such conditions, the atoms can merge into states called "solitons."

To form solitons, the team manipulated the BECs into groups with balanced quantum pressures, pushing the clusters apart while having the presence of attractive forces between the atoms.

Solitons are believed to pass though each other without slowing down or changing shape. The researchers, however, found that in certain collisions, solitons moved toward one another, maintained a minimum distance from each other and then bounced away from the collision.

It's as if the solitons merely passed through one another, but didn't occupy the same space. Hulet explained it's because of the "wave packet" interference.

One of the solitons was positively charged while the other is negatively charged. The probability of the pair being in the same spot is zero as they cancel out one another.

The team carried out the experiment with about thousands of soliton collisions and achieved various results. In some cases, solitons passed though one another while in other runs, solitons just bounced off their counterparts.

The difference can be explained by one defining feature of a soliton that researchers couldn't control -- its phase.

"In the out-of-phase case, the one with the gap, we still saw the gap but we also saw the larger soliton emerge unfazed on the other side of the gap. In other words, it jumped through the gap," Hulet concluded.

The findings recently appeared in the journal, Nature Physics.

TagsSolitons, BECs, Bose Einstein Condensates, Atoms in absolute zero, Disappearing act