Establishing secure data communication necessitates secure key exchange over a public channel. Quantum key distribution (QKD), which leverages the principles of quantum physics, can achieve this with information-theoretic security. The discrete modulated (DM) continuous variable (CV) QKD protocol, in particular, is a suitable candidate for large-scale deployment of quantum-safe communication due to its simplicity and compatibility with standard high-speed telecommunication technology. Here, we present the first experimental demonstration of a four-state DM CVQKD system, successfully generating composable finite-size keys, secure against collective attacks over a 20 km fiber channel with 2.3 \times 10^{9} coherent quantum states, achieving a positive composable key rate of 11.04 \times 10^{-3} bits/symbol. This accomplishment is enabled by using an advanced security proof, meticulously selecting its parameters, and the fast, stable operation of the system. Our results mark a significant step toward the large-scale deployment of practical, high-performance, cost-effective, and highly secure quantum key distribution networks using standard telecommunication components.
@article{arxiv.2410.13702,
title = {Experimental composable key distribution using discrete-modulated continuous variable quantum cryptography},
author = {Adnan A. E. Hajomer and Florian Kanitschar and Nitin Jain and Michael Hentschel and Runjia Zhang and Norbert Lütkenhaus and Ulrik L. Andersen and Christoph Pacher and Tobias Gehring},
journal= {arXiv preprint arXiv:2410.13702},
year = {2025}
}