Bell inequalities and density matrix for polarization entangled photons out of a two-photon cascade in a single quantum dot

TL;DR

This paper models the entangled photon states generated in quantum dots, analyzing how various physical mechanisms affect entanglement fidelity and Bell inequality violations, with implications for quantum information applications.

Contribution

It provides an analytical framework linking physical decoherence mechanisms to entanglement quality in quantum dot photon pairs.

Findings

Spontaneous emission enhancement improves entanglement fidelity.

Threshold conditions for Bell inequality violation are derived.

Dephasing and energy splitting can destroy entanglement.

Abstract

We theoretically investigate the joint photodetection probabilities of the biexciton-exciton cascade in single semiconductor quantum dots and analytically derive the density matrix and the Bell's inequalities of the entangled state. Our model includes different mechanisms that may spoil or even destroy entanglement such as dephasing, energy splitting of the relay excitonic states and incoherent population exchange between these relay levels. We explicitly relate the fidelity of entanglement to the dynamics of these processes and derive a threshold for violation of Bell's inequalities. Applied to standard InAs/GaAs self-assembled quantum dots, our model indicates that spontaneous emission enhancement of the excitonic states by cavity effects increases the fidelity of entanglement to a value allowing for violation of Bell's inequalities.