An entangled two photon source using biexciton emission of an asymmetric quantum dot in a cavity

TL;DR

This paper explores a scheme using asymmetric quantum dots in a cavity to generate entangled photon pairs, aiming to recover polarization entanglement despite asymmetry-induced frequency entanglement.

Contribution

It demonstrates how erasing frequency 'which-path' information in asymmetric quantum dots can recover polarization entanglement in emitted photon pairs.

Findings

Ideal cavities produce maximally entangled photon pairs.

Non-ideal cavities can still generate partially entangled pairs.

Photon pairs can violate Bell inequalities under certain conditions.

Abstract

A semiconductor based scheme has been proposed for generating entangled photon pairs from the radiative decay of an electrically-pumped biexciton in a quantum dot. Symmetric dots produce polarisation entanglement, but experimentally-realised asymmetric dots produce photons entangled in both polarisation and frequency. In this work, we investigate the possibility of erasing the `which-path' information contained in the frequencies of the photons produced by asymmetric quantum dots to recover polarisation-entangled photons. We consider a biexciton with non-degenerate intermediate excitonic states in a leaky optical cavity with pairs of degenerate cavity modes close to the non-degenerate exciton transition frequencies. An open quantum system approach is used to compute the polarisation entanglement of the two-photon state after it escapes from the cavity, measured by the visibility of two-photon interference fringes. We explicitly relate the two-photon visibility to the degree of Bell-inequality violation, deriving a threshold at which Bell-inequality violations will be observed. Our results show that an ideal cavity will produce maximally polarisation-entangled photon pairs, and even a non-ideal cavity will produce partially entangled photon pairs capable of violating a Bell-inequality.