Entropy reduction by motional sideband excitation

Abstract

EVERYONE is intuitively familiar with the second law of thermodynamics: the disorder in any closed system can only increase with time. A familiar example is the spreading of a scent through a room. It is also well known that the spreading greatly accelerates when exterior agents are at work, for example, a stirrer. The reverse task of "bottling up" the diffused scent back in the flask from which it expanded is much more difficult. So if one had somehow succeeded in collecting a cloud of particles in a vacuum at the bottom of a suitable potential well, as would be desirable in removing Doppler shifts in coherent spectroscopy or even in nuclear fusion machines, there will be all sorts of effects at work to spread the particles out again. The principle of entropy reduction by motional sideband excitation1 could be effective in re-collecting the spread out cloud at the bottom of the well. © 1976 Nature Publishing Group.