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  • Open Access

Realistic threat models for fiber and free-space continuous variable quantum key distribution

Zhiyue Zuo

Masoud Ghalaii

Stefano Pirandola*

  • *Contact author: stefano.pirandola@york.ac.uk
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Phys. Rev. Research 8, 013185 – Published 19 February, 2026

DOI: https://doi.org/10.1103/hq32-x7gt

Abstract

Future global quantum communication networks, or quantum internet, will realize high-rate secure communication and entanglement distribution for large-scale users over long distances. Continuous variable (CV) quantum key distribution (QKD) provides a powerful setting for secure quantum communications, thanks to the use of room-temperature off-the-shelf optical devices and the potential to reach high rates. However, the achievable performance of CV-QKD protocols is fundamentally limited by the fact that they appear to be fragile to both loss and noise. In this study, we provide a general framework for analyzing the composable finite-size security of CV-QKD with Gaussian-modulated coherent-state (GMCS) protocol under various levels of trust for the loss and noise experienced by the users of the protocol. Our work is comprehensive of several practical scenarios, encompassing both active and passive eavesdropping configurations, with both wired (i.e., fiber-based) and wireless (i.e., free-space and satellite-based) quantum communication channels. Our numerical results evaluate the robustness of the GMCS protocol under varying levels of trust and demonstrate that it is difficult for a practical protocol to remain robust against untrusted loss at the transmitter. In the wireless case, we analyze a scenario with a sun-synchronous satellite, showing that its key distribution rate, even with the worst level of trust, can outperform a ground chain of ideal quantum repeaters. Our results indicate that—when it comes to engineering and optimizing quantum-safe networks—it is essential to mitigate the shortcomings caused by critical trade-offs between rate performance, trust level, system noise, and communication distance.

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Phys. Rev. Research 8, 013185– Published 19 February, 2026
  • Received 8 October 2025
  • Accepted 21 January 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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