  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.
