Influence of Hyperfine Interaction on the Entanglement of Photons Generated by Biexciton Recombination

TL;DR

This paper theoretically studies how hyperfine interactions and fine structure splitting affect photon entanglement in quantum dots, revealing combined decoherence effects and potential mitigation strategies through nuclear spin polarization.

Contribution

It provides a detailed analysis of hyperfine interaction effects on photon entanglement and explores methods to reduce decoherence via nuclear spin polarization and magnetic fields.

Findings

FSS and hyperfine interactions jointly cause entanglement loss.

Partial nuclear spin polarization can enhance entanglement.

External magnetic fields influence decoherence mitigation.

Abstract

The quantum state of the emitted light from the cascade recombination of a biexciton in a quantum dot is theoretically investigated including exciton fine structure splitting (FSS) and electron-nuclear spin hyperfine interactions. In an ideal situation, the emitted photons are entangled in polarization making the biexciton recombination process a candidate source of entangled photons necessary for the growing field of quantum communication and computation. The coherence of the exciton states in real quantum dots is affected by a finite FSS and the hyperfine interactions via the effective magnetic field known as the Overhauser field. We investigate the influence of both sources of decoherence and find that although the FSS combined with a stochastic exciton lifetime is responsible for the main loss of entanglement, the two effects cannot be minimized independently of each other. Furthermore, we examine the possibility of reducing the decoherence from the Overhauser field by partially polarizing the nuclear spins and applying an external magnetic field. We find that an increase in entanglement depends on the degree as well as the direction of the nuclear spin polarization.