Conditional preparation of single photons using parametric downconversion: A recipe for purity

TL;DR

This paper presents a numerical model for creating pure heralded single photons via group velocity matched parametric downconversion, addressing experimental challenges like focusing effects and providing guidelines for source construction.

Contribution

It introduces a detailed numerical model that guides the design of pure single-photon sources, considering focusing effects that impact spectral factorability.

Findings

Model accurately predicts spectral correlations in photon pairs

Experimental measurements agree with the model's predictions

Provides specific design criteria for pure single-photon sources

Abstract

In an experiment reported recently [Phys. Rev. Lett. 100, 133601 (2008)], we demonstrated that, through group velocity matched parametric downconversion, heralded single photons can be generated in pure quantum states without spectral filtering. The technique relies on factorable photon pair production, initially developed theoretically in the strict collinear regime; focusing - required in any experimental implementation - can ruin this factorability. Here we present the numerical model used to design our single photon sources and minimize spectral correlations in the light of such experimental considerations. Furthermore, we show that the results of our model are in good agreement with measurements made on the photon pairs and give a detailed description of the exact requirements for constructing this type of source.