Quantum key distribution over a metropolitan network using an integrated photonics-based prototype

Abstract

Transitioning quantum key distribution (QKD) toward industrial-scale deployment requires the development of practical, stable, resilient, and cost-effective hardware that can be manufactured at large scales. In this work, we present a high-speed (1.25 GHz), field-deployable QKD prototype based on integrated photonics, consolidated into standard 19-in. rack-compatible units. This prototype leverages integrated photonics to address the requirements for autonomous long-term stability in metropolitan settings. By optimizing the laser and detection parameters and implementing a tailored temporal filtering scheme, our system supports key exchange over 100 km of optical fiber without the requirement for chromatic dispersion compensation. We demonstrate continuous key exchange over a deployed metropolitan optical fiber link, where the prototype maintained stable, uninterrupted operation across a measurement spanning more than 12 day–night cycles without manual intervention. Furthermore, the system's performance limits were characterized by extending the channel with fiber spools and extra attenuation on the receiver side, demonstrating continuous key exchange up to 105 km without chromatic dispersion compensation.