The transport properties of ultracold gases can provide insight into many-body systems that are less tractable experimentally, such as quark– gluon plasmas or high-temperature superconductors. Many such systems are subjects of a recent interest in perfect fluids (see the special issue of PHYSICS TODAY, May 2010).
Thus, when MIT researchers led by Martin Zwierlein recently learned to spatially separate the spin-up and spin-down components of a trapped gas of strongly interacting Fermi atoms, they explored the transport of spins by sending two atomic clouds of opposite spin traveling toward one another. It was not clear what the outcome would be. Perhaps the atoms of opposite spin would pair up, forming a superfluid. Or maybe the spins would remain separate, with the high collision rate of the strongly interacting atoms greatly slowing the time for the two clouds to merge.
The researchers observed far more dramatic and unexpected behavior.1...
