Free‐Space Continuous‐Variable Quantum Key Distribution Under Temporal Channel Dynamics
Shengzhi Xu, Ming Li, Yuxin Shen +5 more
ABSTRACT Temporal dynamics of free‐space continuous‐variable quantum key distribution (CV‐QKD) are intrinsically complicated by atmospheric turbulence‐induced channel fluctuations. The finite‐state Markov (FSM) framework provides a promising approach for mapping temporal evolution into state transitions. However, its application to CV‐QKD remains challenging due to the need for accurate characterization of both channel statistics and temporal correlations. Here, we derive the joint probability density function (PDF) of channel transmittance and its time derivative for log‐normal (LN) and Gamma–Gamma (GG) turbulence models. Based on a spectral‐domain analytical (SDA) approach incorporating inner‐ and outer‐scale effects, we derive temporal channel parameters and quantify the impact of adaptive optics (AO). Furthermore, the level crossing rate (LCR) of channel loss is derived to construct state transition probabilities (STPs) for the FSM framework, which is then employed to predict the temporal evolution of channel transmittance and achievable secret key rate (SKR).Results demonstrate that the proposed FSM framework accurately captures temporal dynamics of free‐space CV‐QKD and turbulence‐induced fluctuations. Under weak turbulence, AO enhances temporal correlation, increases mean SKR, and suppresses short‐term SKR fluctuations. Under strong turbulence, AO improves mean SKR but provides limited enhancement of temporal correlation and fluctuation suppression due to physical constraints.
Advanced Quantum Technologies•Sep 1, 2026•0 citations