Effects of cavity birefringence in polarisation-encoded quantum networks

TL;DR

This paper investigates how cavity birefringence affects the fidelity of polarization-encoded quantum entanglement in quantum networks, highlighting potential limitations and proposing remedies for systems with unavoidable birefringence.

Contribution

It demonstrates the detrimental impact of cavity birefringence on remote entanglement fidelity and proposes two methods to mitigate these effects when cavity design cannot be optimized.

Findings

Mirror birefringence causes polarization oscillations that reduce entanglement fidelity.

Minimizing mirror ellipticity is the best way to prevent birefringence effects.

Even small birefringence can significantly impair quantum network performance.

Abstract

The generation of entanglement between distant atoms via single photons is the basis for networked quantum computing, a promising route to large-scale trapped-ion and trapped-atom processors. Locating the emitter within an optical cavity provides an efficient matter-light interface, but mirror-induced birefringence within the cavity introduces time-dependence to the polarisation of the photons produced. We show that such `polarisation oscillation' effects can lead to severe loss of fidelity in the context of two-photon, polarisation encoded measurement-based remote entanglement schemes. It is always preferable to suppress these errors at source by minimising mirror ellipticity, but we propose two remedies for systems where this cannot be achieved. We conclude that even modest cavity birefringence can be detrimental to remote entanglement performance, to an extent that may limit the suitability of polarisation-encoded schemes for large-scale quantum networks.