The optical architecture of a heterogenous quantum network deployed in production facilities

TL;DR

This paper describes the design and validation of a heterogeneous quantum network integrated into existing production facilities, ensuring quantum-classical interoperability and compliance with standards.

Contribution

It presents practical solutions for deploying quantum communication modules from multiple vendors in real-world telecom networks, validated in the Madrid quantum network.

Findings

Successful integration of quantum and classical signals over 130 km of fiber.

Maintained legacy traffic while implementing quantum key distribution modules.

Ensured interoperability and compliance with standards in a production environment.

Abstract

Quantum Communications promise advances in cryptography, quantum computing and clock synchronisation, among other emerging applications. However, communication based on quantum phenomena requires an extreme level of isolation from external disturbances, complicating the co-propagation of quantum and classical signals. The challenge is greater when deploying networks that are both heterogeneous (e.g., multiple vendors) and installed in production facilities, given that this type of infrastructure already supports networks loaded with their own requirements. Moreover, to achieve a broad acceptance among network operators, the joint management and operation of quantum and classical resources, compliance with standards, and legal and quality assurance need to be addressed. This article presents solutions to the aforementioned challenges validated in the Madrid quantum network during the implementation of the projects CiViC and OpenQKD. This network was designed to integrate quantum communications in the telecommunications ecosystem by installing quantum-key-distribution modules from multiple providers in production nodes of two different operators. The modules were connected through an optically-switched network with more than 130~km of deployed optical fibre. The tests were done in compliance with strict service level agreements that protected the legacy traffic of the pre-existing classical network. The goal was to ensure full quantum-classical interoperability at all levels, while limiting the modifications to optical transport and encryption and complying with relevant standards. This effort is intended to lay the foundation for large-scale quantum network deployments.