Hidden anisotropy controls spin-photon entanglement in a charged quantum dot

TL;DR

This paper investigates how hidden anisotropy in quantum dots influences spin-photon entanglement, revealing that controlling anisotropy and excitation conditions can significantly improve entanglement fidelity for quantum technologies.

Contribution

It provides both theoretical and experimental insights into the impact of quantum dot anisotropy on spin-photon entanglement, and identifies optimal conditions for maximizing entanglement fidelity.

Findings

Spin-photon entanglement is strongly affected by quantum dot anisotropy.

Time-filtered Bell state fidelity can reach 94% with optimal conditions.

Specific magnetic field and polarization directions enhance entanglement.

Abstract

Photon entanglement is indispensable for optical quantum technologies. Measurement-based optical quantum computing and all-optical quantum networks rely on multiphoton cluster states consisting of indistinguishable entangled photons. A promising method for creating such cluster states on demand is spin-photon entanglement using the spin of a resident charge carrier in a quantum dot, precessing in a weak external magnetic field. In this work, we show theoretically and experimentally that spin-photon entanglement is strongly affected by the hidden anisotropy of quantum dots, which can arise from mechanical stress, shape anisotropy and even specific crystal structure. In the measurements of time-resolved photoluminescence and cross-polarized second-order photon correlation function in a magnetic field, the anisotropy manifests itself in the spin dynamics and, as a consequence, in the spin-photon concurrence. The measured time-filtered spin-photon Bell state fidelity depends strongly on the excitation polarization and reaches an extremely high value of 94% at maximum. We specify the magnetic field and excitation polarization directions that maximize spin-photon entanglement and thereby enhance the fidelity of multiphoton entangled states.