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Experimental quantum key distribution certified by Bell's theorem

Abstract

Cryptographic key exchange protocols traditionally rely on computational conjectures such as the hardness of prime factorization1 to provide security against eavesdropping attacks. Remarkably, quantum key distribution protocols such as the Bennett–Brassard scheme2 provide information-theoretic security against such attacks, a much stronger form of security unreachable by classical means. However, quantum protocols realized so far are subject to a new class of attacks exploiting a mismatch between the quantum states or measurements implemented and their theoretical modelling, as demonstrated in numerous experiments3,4,5,6. Here we present the experimental realization of a complete quantum key distribution protocol immune to these vulnerabilities, following Ekert’s pioneering proposal7 to use entanglement to bound an adversary’s information from Bell’s theorem8. By combining theoretical developments with an improved optical fibre link generating entanglement between two trapped-ion qubits, we obtain 95,628 key bits with device-independent security9,10,11,12 from 1.5 million Bell pairs created during eight hours of run time. We take steps to ensure that information on the measurement results is inaccessible to an eavesdropper. These measurements are performed without space-like separation. Our result shows that provably secure cryptography under general assumptions is possible with real-world devices, and paves the way for further quantum information applications based on the device-independence principle.

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Fig. 1: DIQKD with trapped ions.
Fig. 2: DIQKD protocol structure.
Fig. 3: Quantum link performance.
Fig. 4: Finite-statistics key rate.

Data availability

The datasets generated during the current study are available from D.P.N. and C.J.B. on reasonable request.

Code availability

The custom code generated during the current study is available from the corresponding authors on reasonable request.

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Acknowledgements

J.-D.B. and E.Y.-Z.T. thank R. Arnon-Friedman for discussions. We thank Sandia National Laboratories for supplying HOA2 ion traps. This work was supported by the UK Engineering and Physical Sciences Research Council Hub in Quantum Computing and Simulation (EP/T001062/1), the EU Quantum Technology Flagship Project AQTION (No. 820495) and the UKRI Fellowship of C.J.B. (MR/S03238X/1). E.Y.-Z.T. and R.R. acknowledge funding by the Swiss National Science Foundation, through the National Centers for Competence in Research QSIT and SwissMAP, and by the Air Force Office of Scientific Research through grant FA9550-19-1-0202. J.-D.B and N.S. acknowledge funding by the Institut de Physique Théorique, Commissariat á l’Énergie Atomique et aux Energies Alternatives and the Region Île-de-France in the framework of DIM SIRTEQ.

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Contributions

D.P.N., P.D., B.C.N., G.A., D.M. and R.S. built and operated the experimental apparatus. D.P.N. and P.D. led the collection of the experimental data and performed the data analysis. J.-D.B. and D.P.N. extracted the key from the raw data. K.I., R.L.U. and J.-D.B. designed the error correction code. J.-D.B., E.Y.-Z.T., N.S., P.S. and R.R. established the detailed protocol steps and derived the corresponding security proof. N.S., J.-D.B., D.P.N. and C.J.B. wrote the manuscript. C.J.B. and D.M.L. supervised the experimental work, and J.-D.B. and N.S. supervised the theoretical work. N.S. and J.-D.B. initiated the project. All authors contributed to the discussion and interpretation of results, and contributed to the manuscript.

Corresponding authors

Correspondence to D. P. Nadlinger, C. J. Ballance, N. Sangouard or J.-D. Bancal.

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C.J.B. is a director of Oxford Ionics. The remaining authors declare no competing interests.

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Nature thanks Marcos Curty, Lynden Shalm and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.

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Nadlinger, D.P., Drmota, P., Nichol, B.C. et al. Experimental quantum key distribution certified by Bell's theorem. Nature 607, 682–686 (2022). https://doi.org/10.1038/s41586-022-04941-5

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