Atmospheric turbulence is the major challenge to satellite-to-ground quantum key distribution (QKD), yet most performance models treat turbulence only through average statistics, masking temporal loss fluctuations that dominate real links. Here we present an end-to-end, time-evolving satellite-to-ground QKD model that embeds a phase-screen description of turbulence into beam propagation, focusing, tracking, adaptive-optics compensation, and single-mode fiber (SMF) coupling. The simulation delivers the instantaneous channel loss L channel ( t ) and thermal photon dark counts D C bgn , from which we estimate the finite-size secret key rate (SKR) and evaluate the performance of turbulence mitigation techniques. For a GEO-to-Lijiang Station link, the optimized configuration enables day-and-night QKD operation under favorable weather conditions, although the daytime link margin remains limited. This study complements conventional time-averaged models by offering a more realistic and detailed framework for analyzing satellite-to-ground QKD performance and the effectiveness of mitigation techniques under time-evolving turbulence.
Atmospheric turbulence is the major challenge to satellite-to-ground quantum key distribution (QKD), yet most performance models treat turbulence only through average statistics, masking temporal loss fluctuations that dominate real links. Here we present an end-to-end, time-evolving satellite-to-ground QKD model that embeds a phase-screen description of turbulence into beam propagation, focusing, tracking, adaptive-optics compensation, and single-mode fiber (SMF) coupling. The simulation delivers the instantaneous channel loss L channel ( t ) and thermal photon dark counts D C bgn , from which we estimate the finite-size secret key rate (SKR) and evaluate the performance of turbulence mitigation techniques. For a GEO-to-Lijiang Station link, the optimized configuration enables day-and-night QKD operation under favorable weather conditions, although the daytime link margin remains limited. This study complements conventional time-averaged models by offering a more realistic and detailed framework for analyzing satellite-to-ground QKD performance and the effectiveness of mitigation techniques under time-evolving turbulence.
Abstract Future quantum communication infrastructures will rely on both terrestrial and space-based links integrating high-performance optical systems engineered for this purpose. In space-based downlinks in particular, the loss budget and the variations in the signal propagation due to atmospheric turbulence effects impose a careful optimization of the coupling of light in single-mode fibers required for interfacing with the receiving stations and the ground networks. In this work, we perform a comprehensive study of the role of adaptive optics (AO) in this optimization, focusing on realistic baseline configurations of prepare-and-measure quantum key distribution, with both discrete and continuous-variable encoding, and including finite-size effects. Our analysis uses existing experimental turbulence datasets at both day and night time to model the coupled signal statistics following a wavefront distortion correction with AO, and allows us to estimate the secret key rate for a range of critical parameters, such as turbulence strength, satellite altitude and ground telescope diameter. The results we derive illustrate the interest of adopting advanced AO techniques in several practical configurations.
Satellite-based quantum key distribution (QKD) offers a pathway to secure global communications, yet its performance is fundamentally constrained by atmospheric turbulence. This paper presents a detailed analysis of the BBM92 entanglement-based protocol under realistic satellite-to-ground conditions using the Hufnagel-Valley turbulence model. We examine the role of key atmospheric factors, including wind speed, ground station altitude, and diurnal variations, on quantum performance metrics across a mean photon number (MPN) range of 0.001-0.3. Results reveal that turbulence strength, captured via the refractive index structure constant, governs channel transmittance through Rytov variance and scintillation index, directly impacting quantum bit error rate (QBER) and secret key rate (SKR). Simulations show that elevated ground stations improve SKR by15−25%, nighttime operation yields40 - 80 %gains compared with daytime, and wind speeds of30m/scan reduce SKR by up to 60% relative to10m/sconditions. Optimal operation lies in the MPN range of 0.1-0.2, beyond which multiphoton noise degrades security as QBER approaches the 9% threshold.
Abstract Free-space ground-to-ground links will be an integral part of future quantum communication networks. The implementation of free-space and fiber links in daylight inter-modal configurations is however still hard to achieve, due to the impact of atmospheric turbulence, which strongly decreases the coupling efficiency into the fiber. In this work, we present a comprehensive model of the performance of a free-space ground-to-ground quantum key distribution (QKD) system based on the efficient-BB84 protocol with active decoy states. Our model takes into account the atmospheric channel contribution, the transmitter and receiver telescope design constraints, the parameters of the quantum source and detectors, and the finite-key analysis to produce a set of requirements and optimal design choices for a QKD system operating under specific channel conditions. The channel attenuation is calculated considering all effects deriving from the atmospheric propagation (absorption, beam broadening, beam wandering, scintillation, and wavefront distortions), as well as the effect of fiber-coupling in the presence of a partial adaptive optics correction with finite control bandwidth. We find that the channel fluctuation statistics must be considered to correctly estimate the effect of the saturation rate of the single-photon detectors, which may otherwise lead to an overestimation of the secret key rate. We further present strategies to minimize the impact of diffuse atmospheric background in daylight operation by means of spectral and temporal filtering.
Abstract For quantum communications, the use of Earth-orbiting satellites to extend distances has gained significant attention in recent years, exemplified in particular by the launch of the Micius satellite in 2016. The performance of applied protocols such as quantum key distribution (QKD) depends significantly on the transmission efficiency through the turbulent atmosphere, which is especially challenging for ground-to-satellite uplink scenarios. Adaptive optics (AO) techniques have been used in astronomical, communication, and other applications to reduce the detrimental effects of turbulence for many years, but their applicability to quantum protocols, and their requirements specifically in the uplink scenario, is not well established. Here, we model the effect of the atmosphere on link efficiency between an Earth station and a satellite using an optical uplink and how AO can help recover from loss due to turbulence. Examining both low Earth orbit and geostationary uplink scenarios, we find that a modest link transmissivity improvement of about 3 dB can be obtained in the case of a coaligned downward beacon, while the link can be dramatically improved, up to 7 dB, using an offset beacon, such as a laser guide star. AO coupled with a laser guide star would thus deliver a significant increase in the secret key generation rate of the QKD ground-to-space uplink system, especially as reductions of channel loss have a favourably nonlinear key-rate response within this high-loss regime.
Satellite-based Quantum Key Distribution (QKD) has emerged as a promising solution for global secure communication beyond the limitations of terrestrial optical fiber networks. However, practical free-space optical (FSO) satellite channels are highly dynamic due to atmospheric turbulence, background radiation, weather variability, and finite transmission durations. Most existing models rely on static channel assumptions and asymptotic secret key rate (SKR) estimations, which do not accurately reflect real-time operational conditions. This paper proposes an AI-assisted real-time satellite Continuous Variable QKD (CV-QKD) simulator that integrates live weather data with machine learning- based hybrid noise prediction to model realistic channel behavior. The predicted noise parameters are incorporated into an adaptive QKD framework to dynamically compute both asymptotic and finite-size corrected SKR values. The system further performs day–night comparative analysis and 24-hour temporal simulation to study channel variations over time. All operational parameters, including predicted noise, adaptive SKR, and finite-size adjustments, are logged for reproducibility and performance evaluation. The proposed work implemented in the QKD simulator bridges the gap between theoretical QKD modeling and practical satellite deployment by introducing environmental awareness, AI-driven channel adaptation, and finite-size security considerations within an interactive visualization platform. This framework provides a scalable and realistic tool for analyzing next-generation satellite quantum communication systems.
Satellite FSO/QKD systems employ free-space optical links between satellites and ground stations to achieve long-distance quantum key distribution. However, these systems face challenges from atmospheric turbulence. This paper introduces a theoretical framework to evaluate the influence of phase fluctuations caused by atmospheric turbulence on the system performance. Mathematical expressions for key performance metrics are derived and validated through Monte- Carlo simulations. Using results from the framework, we provide a recommended system setup to fulfil the QKD performance requirements under different atmospheric turbulence conditions.