Abstract High-altitude platforms (HAPs) offer enhanced channel transmissivity compared to satellite-based links for free-space continuous-variable quantum key distribution. However, the inherent non-stationarity of the atmospheric channel, dominated by turbulence-induced fading, poses significant challenges to link stability and the consistent maximization of the secret key rate (SKR). To address this, real-time dynamic optimization of system parameters is essential for adapting to channel fluctuations. This study establishes a comprehensive physical transmission model for HAP uplinks to elucidate the impact mechanisms of the initial beam waist and transmitter modulation variance on the SKR. We quantitatively evaluate the performance gains yielded by single-parameter independent optimization versus dual-parameter joint optimization strategies. while joint parameter optimization yields the theoretical performance upper bound, dynamic regulation of the modulation variance emerges as the decisive factor in improving the signal-to-noise ratio and maximizing the SKR. Given the high hardware complexity and response latency associated with adaptive optical zooming mechanisms, we demonstrate that the ‘modulation variance-only’ optimization strategy constitutes the optimal engineering solution. This approach achieves quasi-optimal performance comparable to the joint strategy while significantly reducing implementation complexity, providing a robust and feasible design paradigm for future HAP-based quantum networks.
Abstract High-altitude platforms (HAPs) offer enhanced channel transmissivity compared to satellite-based links for free-space continuous-variable quantum key distribution. However, the inherent non-stationarity of the atmospheric channel, dominated by turbulence-induced fading, poses significant challenges to link stability and the consistent maximization of the secret key rate (SKR). To address this, real-time dynamic optimization of system parameters is essential for adapting to channel fluctuations. This study establishes a comprehensive physical transmission model for HAP uplinks to elucidate the impact mechanisms of the initial beam waist and transmitter modulation variance on the SKR. We quantitatively evaluate the performance gains yielded by single-parameter independent optimization versus dual-parameter joint optimization strategies. while joint parameter optimization yields the theoretical performance upper bound, dynamic regulation of the modulation variance emerges as the decisive factor in improving the signal-to-noise ratio and maximizing the SKR. Given the high hardware complexity and response latency associated with adaptive optical zooming mechanisms, we demonstrate that the ‘modulation variance-only’ optimization strategy constitutes the optimal engineering solution. This approach achieves quasi-optimal performance comparable to the joint strategy while significantly reducing implementation complexity, providing a robust and feasible design paradigm for future HAP-based quantum networks.
Abstract Driven by the necessitates of wide-area quantum secure communication networks, ground-to-satellite quantum key distribution (QKD) has been highlighted in the field of quantum information. Continuous variable QKD (CV-QKD) shows the advantages of a high secure key rate generation and compatibility in the fiber channel, but the communication range is limited by low attenuation tolerance. In this study, the feasibility of the uplink CV-QKD for Very Low Earth Orbit satellite is studied, and the influence of practical factors such as atmospheric turbulence and beam pointing errors under dynamic time-varying satellite orbital parameters is analyzed to model realistic transmission channels. A parameter optimization scheme for orbital parameters, spot size, receiving telescope aperture, and modulation variance has been proposed to enhance the performance of the actual uplink CV-QKD, providing a reference for parameter selection in CV-QKD experiments.
Abstract In the contemporary digital era, ensuring the security of sensitive data and communication is of paramount significance. Encryption methods have been widely employed to safeguard data transmission over public channels. However, the exponential growth in computational power has led to concerns regarding the potential vulnerability of encryption methods. Consequently, breaking encryption poses a significant threat to data privacy. In response to these challenges, the field of quantum cryptography has emerged as a promising solution, offering a fundamentally unbreakable approach to secure communication. One of the key advancements in quantum cryptography is quantum key distribution (QKD). This secure communication mechanism relies on the principles of quantum mechanics to generate encryption keys, enabling secure information exchange between parties. This paper focuses on analysis of the quantum channel between the optical ground station (OGS) and the high-altitude platform System (HAPS). The research involves a meticulous examination and optimization of various system parameters such as performance secret key rate (SKR), electronic noise, modulation variance, and zenith angle. Remarkably, the SKR for a HAPS operating at a vertical altitude of 20 km, with a zenith angle of 20 degrees and a pulse generation rate of 500 MHz, is approximately 84 Mb/s and 44.5 Mb/s for homodyne and heterodyne detection, respectively. This information highlights the potential of quantum cryptography in providing secure communication channels that are resilient to cryptographic attacks.
This letter investigates a continuous-variable quantum key distribution (CV-QKD) protocol based on Gaussian-modulated coherent states over unmanned aerial vehicle (UAV)-based free-space optical (FSO) links. A realistic fading channel model is developed, including atmospheric turbulence, extinction, and UAV-induced pointing errors. We perform distance-dependent modulation variance optimization to maximize the secret key rate (SKR) under three scenarios: asymptotic, finite-block size (FBS), and FBS with adaptive optics (AO), based on numerical simulations incorporating a realistic UAV-FSO channel model. The results show that finite-size effects reduce the secure transmission range to ~800 m, while AO extends it to ~930 m. Furthermore, optimal modulation improves key rates by up to 40% compared to fixed modulation. This is the first work to jointly model UAV-FSO channel fluctuations, optimize modulation, and quantify finite-size security with AO, confirming the feasibility of CV-QKD for UAV-based communications.
Continuous variable quantum key distribution (CV-QKD) has emerged as a promising candidate for quantum-secure communication due to its experimentally demonstrated high key rates in fiber-optic channels. However, the feasibility of discrete modulation CV-QKD in satellite-to-ground downlinks remains an open question due to practical challenges such as high transmission loss, limited communication windows, and atmospheric turbulence. In this work, a comprehensive framework is proposed to evaluate the feasibility of discrete modulation CV-QKD by integrating orbital dynamics and atmospheric channel models, and to comprehensively analyze the influence of the parameter space on free-space discrete modulation CV-QKD. To achieve this, a free-space CV-QKD simulation platform is employed, which calculates the elevation angle and transmission distance based on precise orbital models, thereby providing a more practical assessment of the key rate for discrete modulation CV-QKD. Simulation results verify the feasibility and practicality of discrete modulation CV-QKD in satellite-based quantum communication systems. Furthermore, the critical factors influencing the key rate performance are identified, and parameter optimization strategies are proposed, providing theoretical support for realizing the future satellite-to-ground discrete modulation CV-QKD.
Abstract For a practical continuous-variable quantum key distribution (CV-QKD) system, the optimization of modulation variance is crucial for promoting protocol performance. The optimization relies on algorithms like local search in general. But the efficiency of local search methods is limited in low latency and limited computing power scenarios due to their high computational consumption. Hence, this optimization approach is infeasible for satellite-based CV-QKD due to satellites’ low power feature. In this paper, a neural network model that directly predicting the optimal modulation variance in nearly real time is proposed for free space gaussian modulated CV-QKD protocols. This work enhances the feasibility of implementing CV-QKD in low-Earth-orbit satellite scenarios, where typical link durations of few seconds demand rapid parameter optimization. Moreover, a simulation platform for free space CV-QKD protocol, which employs the precise orbital model to extract the elevation angle and the transmission length, is designed and developed to generate training sets that make the neural network model more practical. Our work can be used as a foundation to support parameter prediction for future quantum communication satellite missions.
The encryption process is essential for ensuring data protection and privacy. However, breaking the encrypted data becomes feasible as computational power grows exponentially. This leads to insecure data transmission over a public channel. Quantum key distribution is a secure communication mechanism that allows shared parties to exchange encryption keys periodically. Furthermore, it has the ability to detect eavesdropping since the error level becomes higher when she attempts to access the communication channel. This paper studies and analysis the performance of the uplink quantum channel between the ground station and the high-altitude platform system (HAPS). In order to achieve optimal performance, the system parameters, such as modulation variance, receiver aperture, and zenith angle influence, are tuned with consideration to the effects of weather conditions and beam wandering. For a HAP at vertical altitude 20 km and with 20° zenith angle and 100 MHz pulse generation rate, a raw key rate of 57 Mb/s and 63 Mb/s is estimated for homodyne and heterodyne detection schemes, respectively.