Mechanistic Understanding of Entanglement and Heralding in Cascade Emitters

TL;DR

This paper provides a theoretical analysis of cascade quantum emitters, exploring their entanglement properties, photon purity, and how decay rates influence entanglement, aiding the design of on-demand single photon sources.

Contribution

It introduces a detailed theoretical model of cascade emitters including polarization and fine structure effects, revealing how decay rate ratios affect entanglement and photon purity.

Findings

Schmidt number depends strongly on decay rate ratios

Purity and entanglement relate to biphoton spectral properties

Extended model includes polarization and emission delay effects

Abstract

Semiconductor quantum light sources are favorable for a wide range of quantum photonic tasks, particularly quantum computing and quantum information processing. Here we theoretically investigate the properties of quantum emitters (QEs) as a source of entangled photons with practical quantum properties including heralding of on-demand single photons. Through the theoretical analysis, we characterize the properties of a cascade (biexciton) emitter, including (1) studies of single-photon purity, (2) investigating the first- and second- order correlation functions, and (3) determining the Schmidt number of the entangled photons. The analytical expression derived for the Schmidt number of the cascade emitters reveals a strong dependence on the ratio of decay rates of the first and second photons. Looking into the joint spectral density of the generated biphotons, we show how the purity and the degree of entanglement are connected to the production of heralded single photons. Our model is further developed to include polarization effects, fine structure splitting, and the emission delay between the exciton and biexciton emission. The extended model offers more details about the underlying mechanism of entangled photon production, and it provides additional degrees of freedom for manipulating the system and characterizing purity of the output photon. The theoretical investigations and the analysis provide a cornerstone for the experimental design and engineering of on-demand single photons.