Quantum Cryptography

High-rate measurement-device-independent quantum cryptography

Quantum cryptography achieves a formidable task: The remote distribution of secret keys by exploiting the fundamental laws of physics. Quantum cryptography is now headed towards solving the practical problem of constructing scalable and secure quantum networks.

Stefano Pirandola, Carlo Ottaviani, Gaetana Spedalieri, Christian Weedbrook, Samuel L. Braunstein, Seth Lloyd, Tobias Gehring, Christian S. Jacobsen & Ulrik L. Andersen.

Nature Photonics 2015, 9: 397–402. doi:10.1038/nphoton.2015.83

A signicant step towards scalable and secure quantum networks has been the introduction of measurement-device independence, where the secret key between two parties is established by the measurement of an untrusted relay. Unfortunately, while qubit-implemented protocols can reach long distances, their key-rates are typically very low, unsuitable for the demands of a metropolitan network. Here we show, theoretically and experimentally, that a solution can come from the use of continuous-variable systems. We design a coherent-state network protocol able to achieve remarkably high key-rates at metropolitan distances, in fact three orders-of-magnitude higher than those currently achieved. Our protocol could be employed to build high-rate quantum networks where devices securely connect to nearby access points or proxy servers.




Ulrik Lund Andersen
DTU Physics
+45 45 25 33 06


Tobias Gehring
Assistant Professor
DTU Physics
+45 93 51 16 49