Improving the fidelity of single photon preparation from conditional down-conversion via asymmetric multiport detection

We discuss the conditional preparation of single photons via parametric down-conversion. This technique is commonly used as a single photon source in modern quantum optics experiments. A significant problem facing this technique is the inability of present day photo-detectors to resolve photon number. This results in mixing with higher photon number terms. To overcome this several techniques have been proposed, including multi-port detection and time-division multiplexing. These techniques help approximate number resolving detection even when using non-number resolving detectors. In this paper we focus on 2-port detection, the simplest such scheme. We show that by making the 2-port device asymmetric the fidelity of prepared photons can be improved