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Coexistence of continuous-variable quantum key distribution and classical data over 120-km fiber

Adnan A. E. Hajomer, Ivan Derkach, Vladyslav C. Usenko, Ulrik L. Andersen, Tobias Gehring

arXiv:2502.17388v2quant-ph

TL;DR

Noise photons from co-propagating classical signals can lower secure key rates and limit QKD transmission distance, despite the infrastructure value of sharing fiber. The authors co-propagate LLO CV-QKD with a fully populated CWDM system and optimize modulation variance to suppress phase-noise-induced excess noise. 120 km (20.17 dB loss) yielded a positive asymptotic key rate, while 100 km (17 dB loss) produced finite-size keys alongside fully populated CWDM channels.

  • Problem

    Noise photons from co-propagating classical signals can lower secure key rates and limit QKD transmission distance, despite the infrastructure value of sharing fiber.

    Source: p. 1

  • Method

    The authors co-propagate LLO CV-QKD with a fully populated CWDM system and optimize modulation variance to suppress phase-noise-induced excess noise.

    Source: p. 1

  • Results

    120 km (20.17 dB loss) yielded a positive asymptotic key rate, while 100 km (17 dB loss) produced finite-size keys alongside fully populated CWDM channels.

    Source: pp. 1, 4

  • Takeaways & Limitations

    The results demonstrate CV-QKD as a viable, plug-and-play solution for integrating QKD with classical data transmission over shared fiber.

    Source: p. 1

    Composable security is limited by block size and information-reconciliation efficiency; deployed-fiber use also requires addressing polarization drift and clock synchronization.

    Source: p. 4

Abstract

from arXiv · show

Integrating quantum key distribution (QKD) with classical data transmission over the same fiber is crucial for scalable quantum-secured communication. However, noise from classical channels limits QKD distance. We demonstrate the longest-distance continuous-variable QKD (CV-QKD) over 120 km (20 dB loss) in the asymptotic regime, and over 100 km (17 dB loss) in the finite-size regime, both coexisting with a fully populated coarse wavelength division multiplexing system. Natural mode filtering of the local oscillator and phase noise mitigation enabled this without additional filtering or wavelength reallocation. Benchmarking against a commercial discrete-variable QKD system and considering finite-size effects confirms the feasibility of CV-QKD as a plug-and-play solution for typical 80-100 km long-haul optical networks. Our results set a record fiber distance for CV-QKD, showing its potential for cost-effective, large-scale deployment in existing network infrastructure.

FULL REFERENCES

The references cover foundational QKD and long-distance demonstrations, coexistence with classical channels, and methods relevant to the paper’s system and analysis.

FULL REFERENCES

  • References [1–6] cover quantum cryptography, QKD protocols, and long-distance quantum key distribution demonstrations.The listed works include continuous-variable QKD over 202.81 km [4] and twin-field QKD over 1000 km [5].Source: FULL REFERENCES · p. 6
  • References [7–16] address coexistence of QKD with classical data channels in fiber networks.The entries include wavelength-division multiplexing, dense WDM, and continuous-variable QKD coexistence studies.Source: FULL REFERENCES · p. 6
  • References [17] and [27] identify work on generating the local oscillator locally in continuous-variable quantum key distribution and a field test of CV-QKD with a true local oscillator, respectively.Source: FULL REFERENCES · p. 6
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