Here is an old article about it – Science Daily
The way I see it, he is using a resonant chamber to create order out of chaos – this takes energy which is taken from the heat of the gas, cooling it. I’m not sure how efficient it could be though. The efficiency is governed by the difference in initial and final temperature. If the gas cools too far it will no longer be enough to excite the resonance and so stop cooling.
It is similar in a way to cooling by lasers. In ultra cold experiments they use lasers to set up a standing EM-wave. Atoms are then trapped in the troughs of the wave and can’t get out – restricting their movement and therfore cooling them.
