Efficient photon counting and single-photon generation using resonant nonlinear optics

The behavior of an atomic double Λ system in the presence of a strong off-resonant classical field and a few-photon resonant quantum field is examined. It is shown that the system possesses properties that allow a single-photon state to be distilled from a multiphoton input wave packet. In addition, the system is also capable of functioning as an efficient photodetector discriminating between one- and two-photon wave packets with high efficiency