PHYSICS: Atom Laser

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Science  19 Oct 2001:
Vol. 294, Issue 5542, pp. 479d
DOI: 10.1126/science.294.5542.479d

The cooling of a cloud of bosonic atoms to such low temperatures that they form a quantum-degenerate gas, or Bose-Einstein condensate, promises to provide the matter analog of the laser, in which a beam of coherent atoms would replace photons. Any temporal fluctuations in the phase of the condensate would be passed on to an extracted beam of atoms forming the atom laser, and thus these fluctuations will limit the coherent properties of such an atom beam. It is thus necessary to know just what those limitations are. So far, however, only the spatial coherence of condensates has been probed, by optically splitting the matter wave and bringing it back together, allowing it to interfere with itself. Information about the temporal properties is lacking.

A technique has now been developed by Köhl et al. that can yield information on the temporal coherence of the condensate. A matter wave is reflected back on itself, and the self-interference between the front of the atom wavepacket and its back end produces a standing wave. The shape and structure of the standing wave can be used to determine the temporal coherence of the condensate.—ISO

Phys. Rev. Lett. 87, 160404 (2001).

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