Coherence of an Entangled Exciton-Photon State

TL;DR

This paper investigates how exciton fine-structure splitting affects photon entanglement in quantum dots, showing that entanglement remains robust despite energy level separations and dephasing effects, supported by both experimental and theoretical analysis.

Contribution

It introduces a theoretical framework accounting for spin-scattering, background light, and dephasing, and measures the novel cross-coherence time parameter.

Findings

Entanglement persists with energy level separations up to 4 micro-eV.

Photon pair entanglement is robust against exciton dephasing.

Introduces and measures the cross-coherence time parameter.

Abstract

We study the effect of the exciton fine-structure splitting on the polarisation-entanglement of photon pairs produced by the biexciton cascade in a single quantum dot. The entanglement is found to persist despite separations between the intermediate energy levels of up to 4 micro-eV. Measurements demonstrate that entanglement of the photon pair is robust to the dephasing of the intermediate exciton state responsible for the first order coherence time of either single photon. We present a theoretical framework taking into account the effects of spin-scattering, background light and dephasing. We distinguish between the first-order coherence time, and a parameter which we measure for the first time and define as the cross-coherence time.