PHYSICS: Stirring a Condensate with a Laser

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Science  29 Sep 2000:
Vol. 289, Issue 5488, pp. 2241a

An object can move through a superfluid without resistance provided that its speed is below a critical value; higher speeds result in the formation of vortices, which are small volumes of normal fluid and superfluid that rotate and dissipate energy. Although the dynamics of these vortices are considered to be crucial in understanding superfluidity, the strong and complex interactions of the superfluid, dissipative forces, and surface effects in most superfluids (such as liquid helium) all combine to obscure observations.

Chevy et al. and Onofrio et al. have studied superfluid motion in a dilute gas of atoms forming a Bose-Einstein condensate (BEC), which they stirred using laser beams. Their results—the determination of the onset of dissipation and the measurement of angular momentum as the stirring rate neared the critical value—combined with the weak interactions between the particles in a dilute gas, suggest that the BEC may be an ideal system for studying superfluidity. — ISO

Acknowledgments

Phys. Rev. Lett. 85, 2223 (2000); Phys. Rev. Lett. 85, 2228 (2000).

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