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Enhancing long-distance continuous-variable quantum key distribution with an error-correcting relay

S. Nibedita Swain1,2,3,*, Ryan J. Marshman3, Josephine Dias3, Matthew S. Winnel3, Alexander S. Solntsev1, and Timothy C. Ralph3

  • 1School of Mathematical and Physical Sciences, University of Technology Sydney, Ultimo, New South Wales 2007, Australia
  • 2Sydney Quantum Academy, Sydney, New South Wales 2000, Australia
  • 3Centre for Quantum Computation and Communication Technology, School of Mathematics and Physics, University of Queensland, Brisbane, Queensland 4072, Australia

  • *Contact author: swain.snibedita@gmail.com
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Phys. Rev. A 114, 012625 – Published 29 July, 2026

DOI: https://doi.org/10.1103/r4pl-mgfy

Abstract

Noiseless linear amplifiers serve as an effective means to enable long-distance continuous-variable (CV) quantum key distribution (QKD), even under realistic conditions with nonunit 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.

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Phys. Rev. A 114, 012625– Published 29 July, 2026
  • Received 11 December 2025
  • Accepted 14 July 2026
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