We discuss a new method for realizing number-resolving and non-demolition photo detectors by strong coupling of light to individual single photon emitters, which act as strong optical non-linearities. As a specific application we show how these elements can be integrated into an error-proof Bell state analyzer, whose efficiency exceeds the best possible performance with linear optics even for a modest atom-field coupling. The methods are error-proof in the sense that every detection event unambiguously projects the photon state onto a Fock or Bell state.
@article{arxiv.1007.3273,
title = {Photon sorters and QND detectors using single photon emitters},
author = {D. Witthaut and M. D. Lukin and A. S. Sørensen},
journal= {arXiv preprint arXiv:1007.3273},
year = {2012}
}