Double-heralded single photons by cascaded downconversion

Abstract

Heralded single photon sources are the subject of intense research owing to their usefulness in metrology and quantum information. These are often created using a pair of photons produced by spontaneous parametric downconversion (SPDC), from which one photon is used to certify the presence of the other. However, multiple-pair production and detector dark counts limit the quality of such sources. Here, we investigate whether cascading two downconversion events to precertify the presence of a photon pair would allow us to reduce these effects. Using analytical calculations and simulations, we find that higher purity photons, as quantified by the heralded second order correlation function, can be obtained for some detector performance ranges.