Noiseless linear amplifiers (NLAs) serve as an effective means to enable long-distance continuous-variable (CV) quantum key distribution (QKD), even under realistic conditions with non-unit reconciliation efficiency. Separately, unitary averaging has been suggested to mitigate some stochastic noise, including phase noise in continuous-variable states. In this work, we combine these two protocols to simultaneously compensate for thermal-loss effects and suppress phase noise, thereby enabling long-distance CV QKD that surpasses the repeaterless bound, the fundamental rate-distance limit, for repeaterless quantum communication systems.
@article{arxiv.2512.11224,
title = {Enhancing Long-distance Continuous-variable Quantum-key-distribution with an Error-correcting Relay},
author = {S. Nibedita Swain and Ryan J. Marshman and Josephine Dias and Alexander S. Solntsev and Timothy C. Ralph},
journal= {arXiv preprint arXiv:2512.11224},
year = {2025}
}