Security of round-robin differential-phase-shift quantum key distribution protocol with correlated light sources

TL;DR

This paper proves the security of the RRDPS quantum key distribution protocol against source imperfections, including pulse correlations, demonstrating its robustness and practicality for real-world high-speed quantum communication systems.

Contribution

The paper provides a simple, experimentally feasible security proof for RRDPS QKD considering pulse correlations, extending its applicability to practical sources.

Findings

Pulse correlations have minimal impact on key rate.

The security proof applies under three simple source assumptions.

The protocol remains robust with correlated light sources.

Abstract

Among various quantum key distribution (QKD) protocols, the round-robin differential-phase-shift (RRDPS) protocol has a unique feature that its security is guaranteed without monitoring any statistics. Moreover, this protocol has a remarkable property of being robust against source imperfections assuming that the emitted pulses are independent. Unfortunately, some experiments confirmed the violation of the independence due to pulse correlations, and therefore the lack of a security proof without taking into account this effect is an obstacle for the security. In this paper, we prove that the RRDPS protocol is secure against any source imperfections by establishing a proof with the pulse correlations. Our proof is simple in the sense that we make only three experimentally simple assumptions for the source. Our numerical simulation based on the proof shows that the long-range pulse correlation does not cause a significant impact on the key rate, which reveals another striking feature of the RRDPS protocol. Our security proof is thus effective and applicable to wide range of practical sources and paves the way to realize truly secure QKD in high-speed systems.