Device-independent quantum key distribution over 100 km with single atoms

TL;DR

This paper demonstrates a device-independent quantum key distribution over 100 km using single atoms, combining advanced entanglement techniques and quantum frequency conversion to achieve secure keys suitable for real-world quantum networks.

Contribution

It presents the first long-distance DI-QKD between single-atom nodes with high-fidelity entanglement and positive key rates over 100 km fiber links.

Findings

Achieved high-fidelity atom-atom entanglement over 100 km

Generated 1.2 million heralded Bell pairs in 624 hours at 11 km

Estimated secure key rate of 0.112 bits per event against general attacks

Abstract

Device-independent quantum key distribution (DI-QKD) is a key application of the quantum internet. We report the realization of DI-QKD between two single-atom nodes linked by 100-km fibers. To improve the entangling rate, single-photon interference is leveraged for entanglement heralding, and quantum frequency conversion is used to reduce fiber loss. A tailored Rydberg-based emission scheme suppresses the photon recoil effect on the atom without introducing noise. We achieved high-fidelity atom-atom entanglement and positive asymptotic key rates for fiber lengths up to 100 km. At 11 km, 1.2 million heralded Bell pairs were prepared over 624 hours, yielding an estimated extractable finite-size secure key rate of 0.112 bits per event against general attacks. Our results close the gap between proof-of-principle quantum network experiments and real-world applications.