Device-Independent Quantum Key Distribution Between Two Ion Trap Nodes

Quantum theory promises that measurements on two entangled systems can yield correlated outcomes that are fundamentally unpredictable to any third party. Following the pioneering work of Ekert [1], we present the experimental realisation of a quantum key distribution (QKD) protocol for cryptography with device-independent security: to prove secrecy, we treat the systems as “black boxes”, relying only on measurement statistics observed during the key generation process. This mitigates many possible attacks on QKD, but requires a great number of observations of a large, detection-loophole-free Bell inequality violation.

We achieve this using two ⁸⁸Sr⁺ ion trap nodes connected by an optical fibre link. A heralded entanglement generation scheme yields about one hundred Bell pairs per second with a fidelity of 96.0(1)%, a new record for optical entanglement of distant matter qubits. We combine this experimental platform with theoretical advances to generate, for the first time, a shared key with device-independent security. Our result [2] demonstrates that provably secure cryptography is possible with real-world devices, and paves the way for further quantum information applications based on the device-independence principle.

[1] PRL 67, 661 (1991)

[2] arXiv:2109.14600