Experimental demonstration of quantum key distribution without monitoring of the signal disturbance

TL;DR

This paper demonstrates a practical implementation of a quantum key distribution protocol that does not require monitoring signal disturbance, enabling secure key sharing over 90 km.

Contribution

First active experimental demonstration of the RRDPS QKD protocol, showing secure key distribution without disturbance monitoring over long distances.

Findings

Successfully distributed secret keys over 90 km

Achieved high stability and low loss in the interferometer

Confirmed feasibility of practical RRDPS QKD implementation

Abstract

Quantum key distribution (QKD) enables two distant users, Alice and Bob, to share secret keys. In existing QKD protocols, an eavesdropper's intervention will inevitably disturb the quantum signals; thus, Alice and Bob must monitor the signal disturbance to place a bound on the potential information leakage. However, T. Sasaki et al. proposed a quite different protocol, named round-robin differential phase shift (RRDPS), in which the amount of eavesdropped information is bounded without monitoring the signal disturbance. Here, we present the first active implementation of the RRDPS protocol. In our experiment, Alice prepares packets of pulses, with each packet being a train with 65 pulses, and the global phase of each packet is randomized. Bob uses a 1-GHz, 1-64-bit actively controlled variable-delay interferometer to realize random switching of the different delays. Benefiting from the large pulse number of each packet, the high stability and low insertion loss of the interferometer, the system can distribute secret key over a distance of 90 km. Our results confirm the feasibility of performing practical QKD with this novel protocol.