Quantum key distribution without detector vulnerabilities using optically seeded lasers

Quantum cryptography immune from detector attacks is realized by the development of a source of indistinguishable laser pulses based on optically seeded gain-switched lasers. Key rates exceeding 1 Mb s −1 are demonstrated in the finite-size regime. Security in quantum cryptography 1 , 2 is continuously challenged by inventive attacks 3 , 4 , 5 , 6 , 7 targeting the real components of a cryptographic set-up, and duly restored by new countermeasures 8 , 9 , 10 to foil them. Owing to their high sensitivity and complex design, detectors are the most frequently attacked components. It was recently shown that two-photon interference 11 from independent light sources can be used to remove any vulnerability from detectors 12 , 13 . This new form of detection-safe quantum key distribution (QKD), termed measurement-device-independent 13 (MDI), has been experimentally demonstrated 13 , 14 , 15 , 16 , 17 , 18 , 19 but with modest key rates. Here, we introduce a new pulsed laser seeding technique to obtain high-visibility interference from gain-switched lasers and thereby perform MDI-QKD with unprecedented key rates in excess of 1 megabit per second in the finite-size regime. This represents a two to six orders of magnitude improvement over existing implementations and supports the new scheme as a practical resource for secure quantum communications.