The behavior of an atomic double lambda 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 multi-photon 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 arbitrarily high efficiency.
@article{arxiv.quant-ph/0304121,
title = {Efficient photon counting and single-photon generation using resonant nonlinear optics},
author = {Mattias Johnsson and Michael Fleischhauer},
journal= {arXiv preprint arXiv:quant-ph/0304121},
year = {2009}
}