Operational entanglement-based quantum key distribution over 50 km of real-field optical fibres

TL;DR

This paper demonstrates a fully operational entanglement-based quantum key distribution network over 50 km of real-field optical fibers in Nice, achieving real-time secret key generation with innovative synchronization and stabilization techniques.

Contribution

It introduces a complete, real-world quantum key distribution system using energy-time entanglement over metropolitan distances, with novel synchronization and stabilization methods.

Findings

Achieved a raw key rate of 40 kbps per channel pair.

Successfully operated a 50 km entanglement-based quantum network in a real city environment.

Enabled real-time secret key generation with integrated post-processing.

Abstract

We present a real field quantum key distribution link based on energy-time entanglement. Three nodes are connected over the city of Nice by means of optical fibers with a total distance of 50\,km. We have implemented a high-quality source of energy-time entangled photon pairs and actively stabilized analysers to project the quantum states, associated with an innovative remote synchronization method of the end stations' clocks which does not require any dedicated channel. The system is compatible with the ITU 100\,GHz standard telecom-grid, through which a raw key rate of 40\,kbps per pair of channels is obtained. A post-treatment software performs all the necessary post-processing procedures enabling to establish secret keys in real time. All of those embedded systems and achieved performance make this network the first fully operational entanglement based metropolitan quantum network to be implemented in real field.