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In a NIST/Colorado atom trap a two-part Bose Einstein condensate of rubidium atoms (one component with spin up, the other spin down) is "stirred" by a laser beam in concert with microwaves. This produces a vortex. In sequences (a) and (b), one species (type 1) of atoms swirl around (the bright ring) while the other species (type 2 and invisible) migrates toward the center. In sequence (c) it is the type 1 atoms (bright blob) that is at the center and type 2 atoms (dark ring) that circulate.
reported by: M.B. Matthews et al., in the 27 Sept issue of Physical Review Letters