The Theory of Atom Lasers

An atom laser is a device which produces a bright, directed, and coherent beam of atoms. An ideal atom laser beam is a single frequency de Broglie matter wave, approximating a noiseless sinusoidal wave; in particular it will have a well defined frequency, phase, and amplitude. Quantum mechanically, such a wave is a mode of the quantised field, and the properties of brightness and well defined phase require the mode to be highly occupied. This is equivalent to requiring Bose degeneracy, and rules out the possibility of a fermionic atom laser. Atom lasers are a recent concept, and to our knowledge the earliest scientific description appeared in 1993 . The first comprehensive papers on matter wave amplification and atom lasers appeared in 1995, and the first experimental demonstration of an atom laser in 1997 . The essential components of an atom laser have been identified by analogy with optical lasers and are illustrated in Fig. 1. They are; a reservoir of atoms from which the laser is pumped, a laser mode in which atoms are accumulated, a pumping (or gain) mechanism which transfers atoms from the reservoir into the laser mode by stimulated transitions, and an output coupler which produces an output beam from the laser mode while preserving its coherence. Many of the possible applications of atom lasers are probably still to be imagined, nevertheless atom lasers have the potential to revolutionise atom