Cooperative terahertz quantum key distribution: Secret key rate analysis and optimization

Abstract

In the recent years, there has been a growing interest in quantum key distribution (QKD) as a promising alternative to conventional cryptographic methods. QKD offers potential for ensuring absolute security in communication networks, leveraging the principles of quantum mechanics. This study diverges from previous research by investigating a cooperative continuous variable QKD (CVQKD) system operating at terahertz (THz) frequencies with multiple input multiple output (MIMO) technology, wherein the source and destination are assisted by a trusted decode-and-forward (DF) relay. Our focus lies on evaluating the secret key rate (SKR) of this system under direct reconciliation conditions and subsequently optimizing power and relay location to maximize the SKR. We address the practical concern of potential eavesdropping between the relay and the destination. Specifically, our analysis centers on the SKR performance of the coherent state-based CVQKD protocol under direct reconciliation conditions. Through numerical simulations, we demonstrate the significant enhancement in SKR achievable through optimization in the cooperative QKD system, yielding several noteworthy insights. © 2024 Elsevier B.V.