Design Considerations for High-purity Heralded Single Photon Sources

TL;DR

This paper investigates practical factors affecting the design and characterization of high-purity heralded single photon sources using parametric downconversion, providing insights for optimizing experimental setups.

Contribution

It offers a comprehensive analysis of real-world issues impacting spectral separability and proposes improved methods for source characterization.

Findings

Realistic pump shapes and crystal imperfections affect spectral separability.

Discretization and spectral range influence purity inference accuracy.

Interference-based methods outperform joint spectral intensity in purity measurement.

Abstract

When building a parametric downconversion photon-pair source with spectrally separable photons, e.g. for making high-purity heralded single photons, two practical issues must be accounted for: the design of the experiment, and its characterization. To address experiment design, we study the impact on spectral separability of realistic (sech shaped and chirped) pump fields, realistic nonlinear crystals with fabrication imperfections, and undesirable PDC generation far from the central PMF peak coming from nonlinearity shaping methods. To address experiment characterization, we study the effect of discretization and spectral range of the measured bi-photon joint spectrum, the difference between inferring separability from the joint spectral amplitude vs. the joint spectral intensity, and advantages of interference experiments for purity characterization over methods based on the joint spectral intensity. This study will be of practical interest to researchers building the next generation of nonlinear sources of separable photon pairs.