Recent efforts to produce single photons via heralding have relied on creating spectrally factorable two-photon states in order to achieve both high purity and high production rate. Through a careful multimode analysis, we find, however, that spectral factorability is not necessary. Utilizing single-mode detection, a similar or better performance can be achieved with non-factorable states. This conclusion rides on the fact that even when using a broadband filter, a single-mode measurement can still be realized, as long as the coherence time of the triggering photons exceeds the measurement window of the on/off detector.
@article{arxiv.1008.2792,
title = {Heralding Single Photons Without Spectral Factorability},
author = {Yu-Ping Huang and Joseph B. Altepeter and Prem Kumar},
journal= {arXiv preprint arXiv:1008.2792},
year = {2010}
}