The active microcavity is adopted as an efficient source of nonclassical light. Using this device, excited with a mode-locked laser at a rate of 100 MHz, single photons are generated over a single field mode with a nonclassical sub-Poissonian distribution. Adiabatic recycling within a multistep Franck-Condon molecular optical-pumping mechanism, characterized by quantum efficiency close to 1, implies a pump self-regularization process leading to a striking $n$-squeezing effect. Replicating the basic single-atom excitation process a beam of quantum photon $|n〉$ states (Fock states) can be created. This represents a significant advance in the fields of basic quantum-mechanical investigation, quantum communication, and quantum cryptography.

• Received 2 June 1995

DOI:https://doi.org/10.1103/PhysRevLett.76.900