Transfer of entanglement from electrons to photons by optical selection rules

TL;DR

This paper investigates the conditions under which entanglement can be transferred from electrons in quantum dots to photons, highlighting the role of optical selection rules and measurement in enabling successful transfer.

Contribution

It reveals that direct unitary transfer of entanglement fails for spin-entangled electrons due to angular momentum constraints, but can succeed with measurement and post-processing.

Findings

Transfer cannot be achieved by unitary evolution alone for certain angular momentum differences.

Measurement of quantum dot angular momentum enables successful entanglement transfer.

Optical selection rules govern the entanglement transfer process.

Abstract

The entanglement transfer from electrons localized in a pair of quantum dots to circularly polarized photons is governed by optical selection rules, enforced by conservation of angular momentum. We point out that the transfer can not be achieved by means of unitary evolution unless the angular momentum of the two initial qubit states differs by 2 units. In particular, for spin-entangled electrons the difference in angular momentum is 1 unit -- so the transfer fails. Nevertheless, the transfer can be successfully completed if the unitary evolution is followed by a measurement of the angular momentum of each quantum dot and post-processing of the photons using the measured values as input.