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This paper derives theoretical limits on how much noise QKD can tolerate and how far secure quantum links can reach, using capacity bounds for qubit Pauli channels and including diffraction constraints for deep-space links. For quantum communication researchers, the value is in knowing the hard ceilings that practical QKD designs and error budgets must respect, rather than in any new hardware result. The bounds apply broadly across BB84-style protocols, so they are useful for judging how close existing fiber and free-space systems are to those limits.
Fundamental Limits on QBER and Distance in Quantum Key Distribution
arXiv:2602.22319v2 Announce Type: replace Abstract: Quantum key distribution (QKD) enables information-theoretic secure communication, yet its ultimate tolerance to noise and achievable transmission distance remain fundamentally constrained. We establish the maximum quantum bit error rate (QBER) compatible with secure QKD and derive corresponding upper bounds on communication distance. Our results follow from a fundamental capacity threshold for qubit Pauli channels and apply to protocols based on two or more mutually unbiased bases, using either single-photon or weak coherent sources. By connecting information-theoretic limits to realistic physical noise models, we obtain universal bounds on achievable distances in fiber and free-space links, including diffraction-limited constraints relevant to deep-space quantum communications. These findings clarify the ultimate noise robustness of QKD and delineate the fundamental boundaries of secure quantum communication.
Abstract:Quantum key distribution (QKD) enables information-theoretic secure communication, yet its ultimate tolerance to noise and achievable transmission distance remain fundamentally constrained. We establish the maximum quantum bit error rate (QBER) compatible with secure QKD and derive corresponding upper bounds on communication distance. Our results follow from a fundamental capacity threshold for qubit Pauli channels and apply to protocols based on two or more mutually unbiased bases, using either single-photon or weak coherent sources. By connecting information-theoretic limits to realistic physical noise models, we obtain universal bounds on achievable distances in fiber and free-space links, including diffraction-limited constraints relevant to deep-space quantum communications. These findings clarify the ultimate noise robustness of QKD and delineate the fundamental boundaries of secure quantum communication.
REVTeX 9 pages. 1 Figure. Accepted version
Quantum Physics (quant-ph); Mathematical Physics (math-ph); Applied Physics (physics.app-ph); Optics (physics.optics); Space Physics (physics.space-ph)
arXiv:2602.22319 [quant-ph]
(or arXiv:2602.22319v2 [quant-ph] for this version)
Phys. Rev. Lett. 137, 110801 (2026)
https://doi.org/10.1103/3bgy-tpy9 DOI(s) linking to related resources
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