Detecting entanglement between quantum emitters using directional emission

TL;DR

This paper demonstrates that the directionality of photon emission from quantum emitters correlates with their entanglement, enabling entanglement estimation through emission measurements, which can benefit quantum network applications.

Contribution

It establishes a quantitative relationship between emission directionality and emitter entanglement, providing a practical method to estimate entanglement via emission statistics.

Findings

Directionality correlates with emitter entanglement over broad parameters.

The relationship breaks down at perfect directionality.

Emission statistics can reliably estimate entanglement (concurrence).

Abstract

Recently, it was shown that quantum interference in a system containing a polarized and unpolarized emitter can allow directional emission of photons into a circulating cavity. Here, we ask whether high directionality of photon emission in this system implies a high degree of quantum correlation between the two emitters. We show that the answer is a qualified "yes", with photon emission directionality and emitter-emitter entanglement showing a monotonic relationship over a broad parameter range. The relationship only breaks down in the limit of perfect directionality. Furthermore, under reasonable assumptions for experimental parameters and stability, we show that the statistics of measured directionality allow a reliable estimate of the concurrence. This result implies that directionality of photon emission in the state preparation stage can be used to determine the entanglement between the emitters, with potential applications to more generic cases including quantum networks.