Quantum Key Distribution networks: specific architecture, protocols and topological design

A global Quantum Key Distribution (QKD) network, as the one developed in the European project SECOQC [1] is an infrastructure capable of realizing long-distance secret key establishment with information-theoretic security. Due to the specificity of their physical layer, the structure and the principle of operation of QKD networks will however significantly differ from the solutions adopted for “classical ” networks. The deployment of QKD networks is indeed far from being straightforward: it implies the con-ception of a network architecture connecting multiple users that may possibly be very far away from each other, all of this while QKD links are currently point-to-point only and intrinsically limited in distance. We will describe the logical architecture we have adopted for QKD networks with the SECOQC project. It is based on the original concept of maintaining a dedicated “network of secrets ” in order to distribute and manage the secret key material produced by QKD devices. We will alo present specific issues related to the development of a stack of network protocols adapted to the specific constraints of such infrastructures [2]. We have also considered QKD networks from a topology viewpoint and study analytically how cost minimization arguments impact on the optimal working points of individual QKD links [3]. We show in particular that, in the perspective of QKD networks, individual QKD links should be operated at an optimal working distance that can be significantly shorter than the maximum distance imposed by detector dark counts. We explain why such results motivate the research of new experimental compromise in practical QKD systems, and illustrate that point by considering the example of the recently developped DPSK QKD system [4]