A quantum key distribution (QKD) system must fulfill the requirement of universal composability to ensure that any cryptographic application (using the QKD system) is also secure. Furthermore, the theoretical proof responsible for security analysis and key generation should cater to the number N of the distributed quantum states being finite in practice. Continuous-variable (CV) QKD based on coherent states, despite being a suitable candidate for integration in the telecom infrastructure, has so far been unable to demonstrate composability as existing proofs require a rather large N for successful key generation. Here we report the first Gaussian-modulated coherent state CVQKD system that is able to overcome these challenges and can generate composable keys secure against collective attacks with N≲3.5×108 coherent states. With this advance, possible due to novel improvements to the security proof and a fast, yet low-noise and highly stable system operation, CVQKD implementations take a significant step towards their discrete-variable counterparts in practicality, performance, and security.
@article{arxiv.2110.09262,
title = {Practical continuous-variable quantum key distribution with composable security},
author = {Nitin Jain and Hou-Man Chin and Hossein Mani and Cosmo Lupo and Dino Solar Nikolic and Arne Kordts and Stefano Pirandola and Thomas Brochmann Pedersen and Matthias Kolb and Bernhard Ömer and Christoph Pacher and Tobias Gehring and Ulrik L. Andersen},
journal= {arXiv preprint arXiv:2110.09262},
year = {2022}
}