Text 2 immiscible quantum liquids

The wavelike overlap of cooled alkali atoms known as Bose Einstein condensation (BEC) represents a new form of condensed matter in which physicists can pursue studies of fluid dynamics, sound propagation, persistent currents, and many of the coherence phenomena occurring in other "super" states such as superfluids and superconductors. One notable BEC innovation introduced in the past year by Wolfgang Ketterle and his colleagues at MIT was the development of an all-optical trap which can hold condensate atoms in a number of distinct (hyperfine) internal states. And just as helium-3 (which has a magnetic substructure) is a more complex superfluid than nonmagnetic helium-4, so the multi-component MIT condensate ought to exhibit behavior not seen in single-component BEC. Indeed, at the New Horizons in Science meeting in Boston last week Ketterle reported that when he immersed his BEC in a uniform magnetic field and a stream of radio waves, those portions of the condensate in different hyperfine states (m=0 and m=1) quickly segregated themselves into alternating domains (differing in energies equivalent to only a few nanokelvins) as if they were oil and vinegar. Furthermore, these layers unexpectedly persist; in effect this arrangement of the condensate constitutes a metastable macroscopically occupied excited state.

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