title: Multi-photon absorption limits to heralded single photon sources.
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 spontaneous four-wave mixing (SFWM) sources in the presence of multi-photon processes. 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 build on these observations to devise a new metric, the quantum utility (QMU), enabling further optimisation of single photon sources.
authors.affiliation: 1] Centre for Ultrahigh-bandwidth Devices for Optical Systems (CUDOS), Institute of Photonics and Optical Science (IPOS), School of Physics, University of Sydney, NSW 2006, Australia [2].
authors.forename: Chad A
authors.initials: CA
authors.lastname: Husko
authors.forename: Alex S
authors.initials: AS
authors.lastname: Clark
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Collins
authors.forename: Alfredo
authors.initials: A
authors.lastname: De Rossi
authors.forename: Sylvain
authors.initials: S
authors.lastname: Combrié
authors.forename: Gaëlle
authors.initials: G
authors.lastname: Lehoucq
authors.forename: Isabella H
authors.initials: IH
authors.lastname: Rey
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Krauss
authors.forename: Chunle
authors.initials: C
authors.lastname: Xiong
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Eggleton