Cavity-Cooling Technique Cools Single Atoms

At Max Planck Institut für Quantenoptik in Garching, Germany, researchers have developed an optical means of cooling single atoms that is at least five times faster than current techniques. Moreover, the approach, which they reported in the March 4 issue of Nature, might enable the cooling of an atom with a stored qubit without disturbing the quantum information, making it suitable for use in novel experiments in quantum information technology.

The technique employs single rubidium-85 atoms in a 120-µm-long high-finesse resonator that is excited by a weak, near-resonant 780.2-nm probe and a stronger, far-detuned 785.3-nm dipole laser. Rather than cooling by spontaneous emissions from the atom, the setup cools by exploiting the strong coupling between the atom and the cavity radiation. As the atom moves away from a node in the standing wave generated in the resonator, the index of refraction of the single-atom medium decreases. As a result, the frequencies of the cavity and of the photons escaping from it increase, carrying off some of the kinetic energy of the atom in the process.

The researchers suggest that because the technique does not need to excite the target to be cooled, it may be used with molecules, Bose-Einstein condensates or with qubit-carrying atoms.