Single-Photon Cooling: Making Maxwell's Demon
Chad Orzel at Uncertain Principles explains an experiment from a group at Texas, putting Maxwell’s Demon to work:
The key to their scheme is the position of the “demon,” which is right along the outer edge of the trap. The only atoms that get far enough out to encounter the demon are necessarily very close to their turning point, and thus moving very slowly. When they drop into the laser trap, they have almost no kinetic energy, and thus a very low temperature. This is exactly the cooling effect you get with Maxwell’s demon.
The experiment described in the paper is basically a proof-of-principle demonstration of the technique. They only loaded a small fraction of the atoms into their laser trap (their highest claimed efficiency was about 2%), and only really cooled the atoms in one dimension. Still, they were able to select out a sample of a few hundred thousand atoms at 4.3μK, starting with a sample at 53μK. This also increased the “phase space density,” which is a combination of position and momentum used as the figure of merit for attempts to get Bose-Einstein Condensation, by a factor of 350.
