Abstract
Quantum key distribution (QKD) can be used to establish a secret key between trusted parties. Many practical use-cases in communication networks, however, involve parties who do not trust each other. A fundamental cryptographic building block for such distrustful scenarios is quantum coin flipping, which has been investigated only in few experimental studies to date, all of which used probabilistic quantum light sources imposing fundamental limitations. Here, we experimentally implement a quantum strong coin flipping protocol using single-photon states and demonstrate a quantum advantage compared to both classical realizations and implementations using faint laser pulses. We achieve this by employing a state-of-the-art deterministic quantum dot light source in combination with fast, random polarization-state encoding enabling sufficiently low quantum bit error ratio. By demonstrating a single-photon quantum advantage in a cryptographic primitive beyond QKD, our work represents a major advance towards the implementation of complex cryptographic tasks in a future quantum internet.
Data availability
The data generated in this study have been deposited in the Zenodo database under accession code https://zenodo.org/records/18436939.
Code availability
All codes produced during this research are available from the corresponding authors upon request.
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Acknowledgements
The authors gratefully acknowledge early contributions to the experimental methodology and software by Timm Gao, experimental support by Bhavana Panchumarthi, Aodhan Corrigan, and Calista Eitel-Porter, as well as technical support by Johannes Schall, Sven Rodt, Stephan Reitzenstein, and Chengao Yang. The authors further acknowledge financial support by the German Federal Ministry of Research, Technology and Space (BMFTR) via the project “QuSecure” (Grant No. 13N14876) within the funding program Photonic Research Germany, the BMFTR joint projects “tubLAN Q.0” (Grant No. 16KISQ087K) as well as QuNET+ICLink (Grant No. 16KIS1967) in the context of the federal government’s research framework in IT-security “Digital. Secure. Sovereign.”, and the Einstein Foundation via the Einstein Research Unit “Quantum Devices”. A.P. also acknowledges financial support by the German Research Foundation (DFG) via the Emmy Noether (Grant No. 418294583). H.L., S.L., H.N., and Z.N. acknowledge financial support by the Chinese Academy of Sciences Project for Young Scientists in Basic Research (Grant No. YSBR-112), the National Natural Science Foundation of China (Grant No. 12494601), and the Innovation Program for Quantum Science and Technology (Grant No. 2021ZD0300801).
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D.A.V. and K.K. set up the quantum coin flipping experiment under the supervision of M.v.H. and T.H.; F.D. and D.A.V. performed the protocol simulations. L.R. designed and fabricated the single-photon source based on the quantum dot wafer material provided/grown by H.L., S.L., H.N., and Z.N. Furthermore, D.A.V., F.D., A.P., and T.H. prepared the paper with inputs from all authors; A.P. supervised the theoretical and T.H. the experimental aspects of the project; T.H. and A.P. jointly conceived the project.
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Vajner, D.A., Kaymazlar, K., Drauschke, F. et al. Single-photon advantage in quantum cryptography beyond QKD. Nat Commun (2026). https://doi.org/10.1038/s41467-026-69995-9
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DOI: https://doi.org/10.1038/s41467-026-69995-9
