Surpassing the PLOB bound in continuous-variable quantum secret sharing using a state-discrimination detector

TL;DR

This paper introduces a novel continuous-variable quantum secret sharing protocol using a state-discrimination detector, surpassing the PLOB bound and improving transmission distance and key rate.

Contribution

It proposes the SDD-CVQSS protocol with a specialized detector, eliminating the need for multiple quantum key distribution links and enhancing performance beyond existing methods.

Findings

Outperforms conventional CVQSS in transmission distance and secret key rate

Surpasses the PLOB bound in secret key rate

Post-selection scheme compensates for performance degradation in long-distance scenarios

Abstract

Continuous-variable quantum secret sharing (CVQSS) is a promising approach to ensuring multi-party information security. While CVQSS offers practical ease of implementation, its present performance remains limited. In this paper, we propose a novel CVQSS protocol integrated with a state-discrimination detector (SDD), dubbed SDD-CVQSS. In particular, we first develop the detailed procedure of SDD-CVQSS, which replaces the traditional coherent detector with an SDD and eliminates the long-standing necessary step of establishing multiple point-to-point quantum key distribution links between all users and the dealer. We then elaborate on the principle of the specifically designed SDD, which can efficiently discriminate mixed states with a much lower error probability. Finally, we construct a security model for SDD-CVQSS and derive its security bound against beam-splitting collective attacks. Numerical simulations show that SDD-CVQSS outperforms conventional CVQSS in both maximum transmission distance and secret key rate, even surpassing the PLOB bound. Additionally, we find that the performance degradation of SDD-CVQSS in long-distance transmission scenarios can be effectively compensated for using a post-selection scheme, providing a feasible way to achieve high-performance CVQSS.