evaporative cooling

Evaporative cooling is a process used in atomic physics experiments to cool atoms down to a few billionths of a degree above absolute zero. The way it works is similar to how a cup of hot coffee cools through evaporation. Atoms are pre-cooled, usually with some kind of laser cooling, and trapped in a manner that imparts no additional energy to the atoms. The warmest atoms are removed from the trap, and the remaining atoms reach a new, lower equilibrium temperature. This process is typically repeated many times, creating small clouds of very cold atoms.