Alexis Rosio

Key exchange over an untrusted communication channel is a crucial step in modern cryptographic protocols, yet current approaches rely on computational assumptions to ensure their security. However, these assumptions may be undermined by an adversary possessing quantum computational capabilities. Quantum Key Distribution (QKD), both in its Discrete Variable (DV) and Continuous Variable (CV) format, is a way to counter this threat. By exploiting the principles of quantum mechanics, QKD enables the development of unconditionally secure protocols, providing a lasting solution that can withstand adversaries regardless of their computational resources. Between DV and CV, the latter is particularly appealing if speed and compatibility with the current fiber telecom infrastructure are considered. In fact, CV-QKD systems can benefit from coherent receivers and widely accessible fiber-based commercial telecom components. Despite this, several practical tasks must be addressed to enable such systems targeting field-deployed real-world scenarios. Among these are the integration of a Quantum Random Number Generator, real-time estimation of key system parameters necessary to compute the Secret Key Rate and network reconfigurability. This study presents a CV-QKD architecture integrating a coherent receiver at the transmitter, enabling secure quantum randomness generation and in-line estimation of key parameters for secret-key-rate computation, advancing the deployment over existing telecom networks.

Quantum Key Distribution (QKD) is a field with a potentially major impact on cybersecurity and telecommunications. QKD protocols allow two distant parties to share a secret key regardless of the capacities of an eavesdropper. Thanks to quantum physics laws, an attempt to measure the signal on a quantum channel will necessarily introduce a disturbance, thus an eavesdropper cannot go unnoticed. The first protocols studied used Discrete Variables (DV), but their implementation requires specific technology such as single-photon detectors. Protocols using so-called continuous variables (CV) allow for the use of standard telecommunication components. Recent studies show that high key rates can be achieved using CV-QKD. Exail coordinates the QKISS project, as part of the development of the European Quantum Communication Infrastructure (EuroQCI), together with Thales SIX, LIP6 (CNRS/Sorbonne Université) and Institut d'Optique (CNRS), with the aim of industrializing CV-QKD systems.We have explored different hardware and software configurations to reduce the excess noise and increase the secret key rate of our prototype system. Based on these studies, we have built a demonstrator, used to realize field tests. We are also inlvolved in different European projects, to concretize the European Quantum Communication Infrastructure.