Heralding pure single photons: a comparision between counter-propagating and co-propagating twin photons

TL;DR

This paper compares counter-propagating and co-propagating geometries in spontaneous parametric down-conversion to optimize the purity of heralded single photons, analyzing how phase-matching affects temporal mode separability.

Contribution

It provides a comparative analysis of two geometries for generating pure heralded single photons, highlighting the impact of phase-matching and group-velocity matching on photon purity.

Findings

Counter-propagating geometry can produce high-purity photons under certain conditions.

Group-velocity matching enhances heralded photon purity in co-propagating setups.

The phase-matching conditions significantly influence the temporal mode separability.

Abstract

We investigate the possibility of generating pure heralded single photons through spontaneous parametric down-conversion comparing the counter-propagating geometry studied in [1] with more conventional co-propagating configurations which enhance the purity of the heralded photon state through the technique of group-velocity matching. We estimate the Schmidt number associated to the temporal modes as a function of the pump pulse duration for three particular configurations, showing how the different phase-matching conditions influences the degree of separability that can be achieved.