Thomas Camus

Quantum Key Distribution (QKD) is a secure communication method that uses quantum mechanics principles to exchange keys between parties. The security of QKD relies on the fundamental properties of quantum physics, making it a crucial technology for achieving highly secure data transmission, in particular in the quantum computer era. Among the impediments of the use of QKD in complex and inter-connected networks is the limited key rate provided by such system, the limited distance between two nodes that want to communicate and the need of confidentiality within the trusted relay. When QKD is implemented in large size networks, running on long distances, the usual solution is to use a lot of intermediate nodes with the consequence of reducing the performance and increasing the need of security inside these intermediate nodes. However, it is still extremely interesting for a user to implement the QKD in such types of topologies because of the high security it allows despite the limitation in bandwidth and the complexity in network topology. We propose a new approach to solve the above-mentioned problems. The core of the solution is to develop a key distribution system that can operate in a new mode; multiplying the bandwidth, in any network topology, while basing the overall security on QKD-exchanged keys.

Quantum Key Distribution (QKD) is arguably the most mature application of principles of quantum mechanics to cryptography, and several lab and field demonstrations have been realized. However the realization of QKD in deployed networks, with high distances and/or complex network architecture is still a challenge. Trusted nodes is a known solution to these issues, but requires the delegation of trust to third parties. Here, we propose a trusted node protocol where the requirements of trust delegation are lowered, with no overhead in the consumption of the key exchanged with QKD, allowing to keep the same secret key rate. This protocol is then applied to 2 links in the Parisian Quantum Network, composed of dark dedicated fibers between 8 nodes in the Parisian region, for a total fiber distance of 57 km. Our results show the overall key exchange with no degradation of the key rate.