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Partially device-independent quantum cryptography in asymmetric networks

Jun-Hao Wei1,2, Shu-Ming Hu1,2, Nuo-Ya Yang1,2, Shuai Zhao3,*, Li Li1,2,4,†, Nai-Le Liu1,2,4,‡, and Kai Chen1,2,4,§

  • *Contact author: zhaoshuai@hdu.edu.cn
  • †Contact author: eidos@ustc.edu.cn
  • ‡Contact author: nlliu@ustc.edu.cn
  • §Contact author: kaichen@ustc.edu.cn
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Phys. Rev. Research 8, 033060 – Published 14 July, 2026

DOI: https://doi.org/10.1103/53w8-6v5z

Abstract

Quantum key distribution (QKD) enables secure key generation between distant users, yet its standard device-dependent implementations rely on fully characterized and accurately modeled devices. Device-independent (DI) QKD removes this assumption by certifying privacy solely from Bell inequality violations, but its stringent experimental demands severely hinder scalability. In realistic quantum networks, asymmetric levels of device trust can naturally arise from diverse implementation conditions across nodes. Motivated by this, we investigate partially DI scenarios in which only a subset of parties operate trusted devices. Built upon the Brown-Fawzi-Fawzi method [Quantum 8, 1445 (2024)], we employ a semidefinite programming hierarchy tailored to estimate the conditional von Neumann entropies in such settings. This approach provides efficiently computable lower bounds on asymptotic rates of cryptographic protocols with broad applicability. By reexamining representative bipartite and tripartite communication tasks under the partially DI framework, we demonstrate that enforcing trust on the devices of a subset of parties never degrades key or randomness expansion rates and, in certain cases, can substantially increase them owing to the network asymmetry. Our results highlight the impact of device trustworthiness on cryptographic security and facilitate scalable implementations in practical asymmetric network architectures.

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Phys. Rev. Research 8, 033060– Published 14 July, 2026
  • Received 3 February 2026
  • Accepted 18 June 2026
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