Multi-photon absorption limits to heralded single photon sources

TL;DR

This paper investigates how multi-photon absorption processes like TPA and ThPA limit the performance of heralded single photon sources in nonlinear photonic devices, providing a new model and a figure of merit for optimization.

Contribution

It introduces a novel model for multi-photon absorption effects in photon sources and proposes the quantum utility metric for source comparison and optimization.

Findings

TPA imposes an intrinsic limit on heralded single photon sources

The model accurately predicts brightness, CAR, and g(2)(0) measurements

Quantum utility (QMU) enables effective source optimization

Abstract

Single photons are of paramount importance to future quantum technologies, including quantum communication and computation. Nonlinear photonic devices using parametric processes offer a straightforward route to generating photons, however additional nonlinear processes may come into play and interfere with these sources. Here we analyse these sources in the presence of multi-photon processes for the first time. We conduct experiments in silicon and gallium indium phosphide photonic crystal waveguides which display inherently different nonlinear absorption processes, namely two-photon (TPA) and three-photon absorption (ThPA), respectively. We develop a novel model capturing these diverse effects which is in excellent quantitative agreement with measurements of brightness, coincidence-to-accidental ratio (CAR) and second-order correlation function g(2)(0), showing that TPA imposes an intrinsic limit on heralded single photon sources. We devise a new figure of merit, the quantum utility (QMU), enabling direct comparison and optimisation of single photon sources.