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Surpassing the loss-noise robustness trade-off in quantum key distribution

Hannah Seabrook1,2,*, Emilien Lavie1, Teodor Strömberg3, Matthew P. Stafford1,2, and Giulia Rubino1,4,†

  • *Contact author: hannah.seabrook@bristol.ac.uk
  • †Contact author: giulia.rubino@bristol.ac.uk
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Phys. Rev. Applied 24, 024072 – Published 29 August, 2025

DOI: https://doi.org/10.1103/xq2l-r4r7

Abstract

Quantum key distribution (QKD) offers a theoretically secure method to share secret keys, yet practical implementations face challenges due to noise and loss over long-distance channels. Traditional QKD protocols require extensive noise compensation, hindering their industrial scalability and lowering the achievable key rates. Alternative protocols encode logical qubits in noise-resilient states but at the cost of using many physical qubits, increasing susceptibility to loss and limiting transmission distance. In this work, we introduce a logical-qubit encoding that uses antisymmetric Bell states in the continuous photonic degrees of freedom, frequency and time. By leveraging the continuous space, we overcome this noise-loss robustness trade-off by minimizing the number of photons per logical qubit while optimizing the encoding resilience over noise fluctuations. We analyze the security of our encoding and demonstrate its robustness compared to existing state-of-the-art protocols. This approach provides a path toward scalable, efficient QKD implementations under realistic noise conditions.

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Phys. Rev. Applied 24, 024072– Published 29 August, 2025
  • Received 17 February 2025
  • Revised 21 July 2025
  • Accepted 23 July 2025
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