BEC in a Circular Waveguide

Bose Einstein condensates (BECs), in which trapped, chilled atoms fall into a single corporate quantum state, have been achieved for several elements of the periodic table and in a variety of trap geometries. Physicists at UC Berkeley have now, for the first time, produced a BEC in a ring-shaped trap about 1 millimeter across. By using an extra magnetic field, in addition to those used to maintain the atoms in the trap to start with, the whole trap can be "tilted," so as to accelerate the atoms up to velocities of about 50-150 mm/sec (or equivalently to energies of about 100 pico-electron-volts per nucleon, as compared to the TeV energies sought for particle physics). After this initial "launch" phase, the atoms are allowed to drift around the ring; they do this not in clumps (as you would have with particles in a colliding-beam storage accelerator) but in a continuously expanding stream. However, starting from the BEC state, the atoms are really more like coherent atom waves smeared out around the ring; they move ballistically and without emitting synchrotron radiation. According to Dan Stamper-Kurn (dmsk@berkeley.edu), potential applications for BEC rings would become possible if parts of the circulating condensate could be made to interfere with other parts. From such an interferometer one could devise gyroscopes or high-precision rotation sensors. Other possible realms of study: quantized circulation, fluid analogues of general relativity, and fluid analogues of SQUID detectors and other superconducting devices. (Gupta et al., Physical Review Letters, upcoming article; lab website at physics.berkeley.edu/research/ultracold )