Single-photon cooling at the limit of trap dynamics: Maxwell's Demon   near maximum efficiency
  We demonstrate a general and efficient informational cooling technique for atoms which is an experimental realization of a one-dimensional Maxwell's Demon. The technique transfers atoms from a magnetic trap into an optical trap via a single spontaneous Raman transition which is discriminatively driven near each atom's classical turning point. In this way, nearly all of the atomic ensemble's kinetic energy in one dimension is removed. We develop a simple analytical model to predict the efficiency of transfer between the traps and provide evidence that the performance is limited only by particle dynamics in the magnetic trap. Transfer efficiencies up to 2.2% are reported. We show that efficiency can be traded for phase-space compression, and we report compression up to a factor of 350. Our results represent a 15-fold improvement over our previous demonstration of the cooling technique. 
S. Travis Bannerman, Gabriel N. Price, Kirsten Viering, and Mark G.   Raizen