On the Purity and Indistinguishability of Down-Converted Photons

TL;DR

This paper presents analytical tools and experimental validation for measuring the purity and indistinguishability of photons generated by SPDC, crucial for quantum information applications.

Contribution

It introduces simple formulas to determine photon purity and indistinguishability from HOM interference patterns, validated by experiments and simulations.

Findings

Analytical formulas accurately extract photon properties from interference data

Experimental results confirm the validity of the formulas

Provides practical tools for quantum photonic source characterization

Abstract

Photons generated by spontaneous parametric down conversion (SPDC) are one of the most useful resources in quantum information science. Two of their most important characteristics are the purity and the indistinguishability, which determine just how useful they are as a resource. We show how these characteristics can both be accessed through Hong, Ou and Mandel (HOM) type interferences using a single pair source. We also provide simple and intuitive analytical formulas to extract their values from the depth of the resulting interference patterns. The validity of these expressions is demonstrated by a comparison with experimental results and numerical simulations. These results provide an essential tool for both engineering SPDC sources and characterizing the quantum states that they emit, which will play an increasingly important role in developing complex quantum photonic experiments.