Ultracold atom

Ultracold atoms are atoms that are maintained at temperatures close to 0 kelvin (absolute zero), typically below temperatures of some tenths of microkelvins (µK). At these temperatures the atom's quantum-mechanical properties become important.

To reach such low temperatures, a combination of several techniques has to be used. First atoms are usually trapped and pre-cooled via laser cooling in a magneto-optical trap. To reach the lowest possible temperature, further cooling is performed using evaporative cooling in a magnetic or optical trap.

Experiments with ultracold atoms are important for understanding quantum phase transition and studying Bose–Einstein condensation (BEC), bosonic superfluidity, quantum magnetism, many-body spin dynamics, Efimov states, Bardeen-Cooper-Schrieffer (BCS) superfluidity and the BEC-BCS crossover.

History

Samples of ultracold atoms are typically prepared through the interactions of a diffuse gas with a laser field. Evidence for radiation pressure, force due to light on atoms, was demonstrated independently by Lebedev, and Nichols and Hull in 1901. In 1933, Otto Frisch demonstrated the deflection of individual sodium particles by light generated from a sodium lamp.