What do We Mean by “An Atom Laser”?
Atom optics is a new field, based on the analogy between atom de Broglie waves and electro-magnetic waves. However, conceptually, the wavefunction of an atom and the electromagnetic field are quite distinct. If there is any conceptual closeness between light waves and atom waves, it can only be through the second-quantized description of many atoms. For Bose atoms, the second-quantized wavefunction operator is analogous to the quantized electromagnetic potential. Thus it is possible to have an atom field with a large coherent amplitude, in the same sense as a photon field in a laser. A device which could produce a coherent beam of atoms in this sense would have radical consequences in atomic and optical physics. In this paper we i) define what we mean by a coherent beam of atoms, ii) identify what is the characteristics of lasers, both for atoms and photons, which produce such a coherent beam, and iii) briefly outline two different proposals for producing an atom laser.