Improving the secure transmission distance of continuous-variable quantum key distribution under limited eavesdropping using a quantum scissor

In this paper, we explore the enhancement of secure transmission distance in continuous-variable quantum key distribution (CV-QKD) under limited eavesdropping conditions by employing a quantum scissor (QS). We derive an analytical expression for the output state and demonstrate that QS significantly extends the secure communication range. Additionally, we analyze the impact of limited eavesdropping on the secret key rate, showing that restricted access to intercepted light improves security compared to an unrestricted eavesdropper scenario. To provide a comprehensive assessment, we investigate both direct and reverse reconciliation schemes. Our numerical simulations and analytical comparisons reveal that QS improves the secure transmission distance in both cases, despite reducing the secret key rate at shorter distances. The results show that QS mitigates the detrimental effects of channel loss, allowing for an extended communication range in CV-QKD systems. These findings highlight the potential of QS as a key tool for enhancing long-distance secure quantum communication in practical scenarios. • Study of secure-distance enhancement in CV-QKD with limited eavesdropping using a QS. • QS improves the maximum secure transmission distance of the CV-QKD protocol. • Key rates under limited eavesdropping are analyzed for both reconciliation types. • Limited eavesdropping yields higher key rates than the fully unrestricted case. • Optimal modulation variance and QS gain that extend protocol range are identified.