Romain Alléaume

Continous-Variable Quantum Key Distribution (CV-QKD) relies on accurate noise calibration at the receiver to ensure the security of quantum communication. Traditional calibration methods often oversimplify noise characteristics, neglecting the impact of local oscillator (LO) noise and the critical role of noise dynamics, which can lead to imprecise Shot Noise Calibration (SNC). Our contributions are threefold: 1) we propose an operational framework for calibration, relying on the notion of stationarity 2) in this framework, we give a method allowing to derive the optimal calibration time 3) leveraging our knowledge of noise dynamics, we introduce a novel SNC method. We demonstrate that our improved calibration techniques offer higher performance and higher tolerance to receiver defects, which can enhance the performance and cost-effectiveness of CV-QKD systems.

We introduce an explicit construction for a key distribution protocol in the Quantum Computational Timelock (QCT) security model, where one assumes that computationally secure encryption may only be broken after a time much longer than the coherence time of available quantum memories. Taking advantage of the QCT assumptions, we build a key distribution protocol called HM-QCT from the Hidden Matching problem for which there exists an exponential gap in one-way communication complexity between classical and quantum strategies.

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.