Classical Control of Quantized Fields: Cavity Qed and the Photon Pistol

By using the double-lambda configuration of energy levels and three classical fields, an atom or ion in a high-Q resonant cavity can be manipulated to create a single-mode quantum state in the cavity that is an arbitrary combination of Fock states for that mode. The same principles of operation can be applied to a cavity with much lower Q in order to produce a "photon pistol", a device that "shoots" one and only one photon when a trigger is pulled, and emits no photons at other times.