A Systematic Noise Analysis for OFDM-based Multi-Carrier Continuous-Variable Quantum Key Distribution

Abstract

Multi-carrier continuous-variable quantum key distribution (MC CV-QKD) offers a practical solution for achieving superior secure key rate (SKR) within metropolitan region. However, the additional noise introduced by MC operation limits the potential SKR improvement. In this work, we perform a systematic noise analysis for orthogonal frequency division multiplexing (OFDM)-based MC CV-QKD that comprehensively accounts for the preparation, propagation, and measurement of MC quantum states. Notably, the MC phase noise, which represents a predominant source of excess noise, is analysed and categorized into two distinct components: common phase error and inter-carrier interference. Furthermore, compared with a single-carrier (SC) system under identical conditions, the MC system can achieve a substantially higher SKR by selecting an appropriate number of subcarriers, even in the presence of additional MC noise. Therefore, this work contributes a viable theoretical framework for fully evaluating the SKR of MC CV-QKD systems.