Device-independent quantum key distribution with spin-coupled cavities

TL;DR

This paper proposes a realistic device-independent quantum key distribution protocol using spin-coupled cavities, enabling high-efficiency measurements and overcoming channel loss issues, with significantly improved key rates over long distances.

Contribution

It introduces a novel DIQKD protocol utilizing light-spin interactions in cavities, allowing heralded entanglement transfer and improved key rates compared to purely optical methods.

Findings

Achieves high key rates over 75 km with realistic parameters.

Heralded spin entanglement mitigates channel loss effects.

Significantly outperforms existing optical DIQKD protocols.

Abstract

Device-independent quantum key distribution (DIQKD) guarantees the security of a shared key without any assumptions on the apparatus used, provided that the observed data violate a Bell inequality. Such violation is challenging experimentally due to channel losses and photo-detection inefficiencies. Here we describe a realistic DIQKD protocol based on interaction between light and spins stored in cavities, which allows a heralded mapping of polarisation entanglement of light onto the spin. The spin state can subsequently be measured with near unit efficiency. Heralding alleviates the effect of channel loss, and as the protocol allows for local heralding, the spin decay is not affected by the communication time between the parties, making Bell inequality violation over an arbitrary distance possible. We compute the achievable key rates of the protocol, based on recent estimates of experimentally accessible parameter values and compare to the other known DIQKD protocol, which is entirely optical. We find significant improvements in terms of key bits per source use. For example we gain about five orders of magnitude over a distance of 75km, for realistic parameter values.