ABSTRACT This study presents a comprehensive feasibility analysis of low Earth orbit (LEO) satellite‐to‐ground downlink communication for quantum key distribution (QKD), focusing on 1550 nm wavelength. This wavelength is selected for its compatibility with terrestrial fibre‐optic networks, allowing the distribution of quantum keys over extended distances. The analysis models a discrete variable decoy state BB84 protocol, emphasising the system's design requirements for the optical ground station (OGS) receiver, including critical parameters that affect single‐mode fibre (SMF) coupling efficiency. Through extended simulations, we assess atmospheric conditions, turbulence effects and adaptive optics (AO) correction to evaluate their impact on light coupling efficiency and achievable key rates. Results highlight the advantage of AO in sustaining secure key rates, particularly under high‐elevation satellite passes, and quantify the key volumes attainable across varying levels of turbulence and additional fibre transmission losses. Our findings demonstrate that LEO satellite‐based QKD downlinks can be feasibly integrated with terrestrial fibre systems, supporting secure key distribution over potentially large geographic areas without requiring OGSs to be trusted nodes. The results of this work provide practical insights into the technical requirements and configurations needed to realise robust satellite‐to‐ground QKD links, laying a foundation for future advancements in global quantum‐secure communication infrastructure.
ABSTRACT This study presents a comprehensive feasibility analysis of low Earth orbit (LEO) satellite‐to‐ground downlink communication for quantum key distribution (QKD), focusing on 1550 nm wavelength. This wavelength is selected for its compatibility with terrestrial fibre‐optic networks, allowing the distribution of quantum keys over extended distances. The analysis models a discrete variable decoy state BB84 protocol, emphasising the system's design requirements for the optical ground station (OGS) receiver, including critical parameters that affect single‐mode fibre (SMF) coupling efficiency. Through extended simulations, we assess atmospheric conditions, turbulence effects and adaptive optics (AO) correction to evaluate their impact on light coupling efficiency and achievable key rates. Results highlight the advantage of AO in sustaining secure key rates, particularly under high‐elevation satellite passes, and quantify the key volumes attainable across varying levels of turbulence and additional fibre transmission losses. Our findings demonstrate that LEO satellite‐based QKD downlinks can be feasibly integrated with terrestrial fibre systems, supporting secure key distribution over potentially large geographic areas without requiring OGSs to be trusted nodes. The results of this work provide practical insights into the technical requirements and configurations needed to realise robust satellite‐to‐ground QKD links, laying a foundation for future advancements in global quantum‐secure communication infrastructure.
This paper presents a comprehensive feasibility analysis designed to model Low Earth Orbit (LEO) satellite-to-ground communications for Quantum Key Distribution (QKD), focusing on the 1550nm wavelength to facilitate the distribution of information through fiber segments. Discrete Variable Decoy State Polarization-based BB84 protocol is assumed whereas various detection setups and environmental conditions are simulated. Our analysis focuses on the receiver's design in terms of aperture and focal length to deliver a general framework by examining the coupling efficiency, a parameter strongly affecting the QKD satellite downlink. Through detailed simulation, we identify optimal configurations and operational parameters for various receiver designs, significantly enhancing the efficiency and reliability of satellite-to-ground QKD systems. The findings offer promising directions for extending the range of QKD systems, potentially revolutionizing secure communications by integrating satellite-transmitted quantum keys with terrestrial fiber networks. This study not only underscores the feasibility of advancing satellite-to-ground QKD technology but also lays the groundwork for future innovations in global quantum communications infrastructure.
Quantum Key Distribution (QKD) is a promising method to guarantee future-proof, information theoretic security. Since optical fibers have an exponential loss with distance, satellite-based QKD solutions are being developed in order to realize long-distance links. Therefore, Optical Ground Stations for QKD (QKD-OGS) need to be designed to enable quantum communication with satellites. Different link configurations will result in different integration options of the QKD-OGS in the terrestrial fiber network and therefore impact its performance. Applicable integration options must be identified and trade-off analysis conducted at the architecture, system and sub-system level. The reference scenario is a Low Earth Orbit (LEO) downlink configuration employing a decoy-state BB84 protocol with polarization encoded qubits at 1550 nm wavelength. The satellite acts as trusted node for implementation of the key distribution between two parties on ground. Furthermore, only direct connections from the satellite to the end-users are considered, i.e. the QKD-OGS does not serve as a trusted-node relay. This results in the selection of three main integration concepts: first, a free-space, end-user QKD-OGS which is located directly at the end-user where the quantum signal is measured directly behind the receiver telescope in free-space; second, a fiber-coupled, end-user QKD-OGS where the quantum signal is coupled into a single-mode fiber and guided to a co-located server room hosting the QKD Receiver system; third, a fiber-coupled, provider QKD-OGS, which reaches several end-users by using a local fiber network. In order to evaluate these three concepts, the comparison parameter is defined to be an estimated factor of suppliable end-users. The estimated comparison factor shows that the fiber-coupled, enduser QKD-OGS can supply 6.7 times more end users than the free-space, end-user QKD-OGS. The fiber-coupled, end-user QKD-OGS can supply 129.7 times more end-users than the free-space, end-user QKD-OGS.
Satellite-based QKD is currently being developed to revolutionize global cryptographic key exchange by facilitating secure communication among remote parties at a global scale. By overcoming the exponential loss of fiber transmission, satellite-to-Earth communication can seamlessly interconnect vast distances as the link budget of such links is sufficient to support QKD links. In terms of this direction, DV-QKD implementations seems to be technologically ahead since key exchange has been experimentally demonstrated to perform much more efficiently by providing key rates that are orders of magnitude higher compared to entanglement-based key exchange. However, the specific requirements to support effectively functional DV-QKD satellite-to-ground links are yet to be defined. This work attempts to define the satellite and ground segment system requirements needed in order to achieve functional QKD service for various satellites orbits (LEO, MEO, and GEO). Finite key size effects are being considered to determine the minimum block sizes that are required for secure key generation between a satellite node and a ground terminal for a single satellite pass. The atmospheric link channel is modeled with consideration of the most important degradation effects such as turbulence and atmospheric and pointing loss. Critical Tx and Rx system parameters, such as the source’s intrinsic Quantum Bit Error Rate (iQBER), the Rx telescope aperture size, and detection efficiency, were investigated in order to define the minimum requirements to establish an operation satellite-to-ground QKD link under specific assumptions. The performance of each downlink scenario was evaluated for the wavelength of 1550 nm in terms of link availability, link budget, and in the distilling of secure key volumes over time. Finally, the feasibility and requirements for distributing the collected space photons via terrestrial telecom fibers was also studied and discussed, leading to the proposal of a more futuristic WDM-enabled satellite QKD architecture. This comprehensive analysis aims to contribute to the advancement and implementation of effective satellite-based QKD systems, which can further exploit the ground fiber segment to realize converged space/terrestrial QKD networks.
Satellite-based Quantum Key Distribution (QKD) is emerging as a cornerstone technology for secure global communication networks, extending quantum-safe key exchange beyond the limitations of terrestrial fiber systems. Achieving scalable and robust space-to-ground QKD links requires careful optimization of optical terminals, channel conditions, and protocol-specific parameters.In this work, we present a system-level analysis of design priorities for satellite QKD networks, using realistic atmospheric conditions modeled with MODTRAN 6 and a simulation tool designed and developed in-house. For discrete-variable (DV) QKD, we analyze how the secret key rate (SKR) varies with satellite altitude for two telescope aperture sizes under representative rural and urban ground station scenarios. Results show that DV-QKD enables secure key distribution over distances compatible with LEO and MEO satellite links when using moderately sized ground telescopes (600mm and 800mm apertures). For continuous-variable (CV) QKD with Gaussian modulation, SKR is analyzed as a function of satellite altitude under the most favorable link conditions identified in the DV-QKD study (800 mm ground aperture and rural environment), indicating that CV-QKD is feasible for secure key exchange with low-altitude LEO satellites, as long as the excess noise remains within low (yet experimentally achievable) levels (≈ 0.045 SNR). Additionally, we establish upper bounds on tolerable excess noise via heatmap analysis, defining the operational regime for secure CV-QKD.These findings provide quantitative guidance for designing scalable, interoperable, and cost-efficient space-to-ground QKD infrastructures, supporting the development of robust global quantum communication networks.
We investigate the feasibility of satellite-to-ground quantum key distribution (QKD) at multi-GHz clock rates, where secure key generation time is constrained, due to low-Earth orbit (LEO) satellite overpasses ( ≈ 300 s). Higher repetition rates offer a direct route to increased secure key rate (SKR), though system performance is fundamentally limited by detector timing jitter, optical coupling losses, and atmospheric turbulence, depending on receiver architecture. We combine finite-key modeling, detailed detector timing characterization, adaptive optics (AO) modeling, and real-time free-space QKD experiments at 1 GHz to evaluate practical receiver configurations based on multi-mode fiber-coupled avalanche photodiodes (MMF-APDs) and single-mode fiber-coupled superconducting nanowire single-photon detectors (SMF-SNSPDs), at projected rates >1 GHz. The results indicate clear operating regimes across a range of atmospheric conditions: MMF-APDs maximize secure key rates below ∼ 1 GHz, mainly due to their low coupling loss. However, low-jitter SMF-SNSPDs are required to obtain positive key rates at higher clock rates—with modeling and measured timing responses of our hardware indicating an estimated optimal operating point near ∼ 7.2 GHz—though AO correction is required for effective single-mode coupling under turbulence. The experimental and projected results provide quantitative performance bounds and realistic design targets for future high-rate satellite QKD systems, while highlighting the technological requirements needed to achieve end-to-end operation beyond the GHz regime.
ABSTRACT This review presents the state of the art in quantum key distribution (QKD) for satellite‐to‐ground free‐space optical links. It first surveys continuous‐variable, discrete‐variable, entanglement‐based, measurement‐device‐independent, and twin‐field protocols, and discusses their feasibility under the losses and time‐varying conditions of orbital passes. It also distinguishes protocol security from practical implementation security. The paper then reviews enabling technologies, including single‐photon sources and detectors, followed by atmospheric impairments, time‐evolving turbulence, aperture averaging, and adaptive optics. Finally, physical channel limits and the trust assumptions of satellite‐network architectures are discussed. Overall, the literature indicates that discrete‐variable decoy‐state BB84 in LEO downlink configurations is the most mature near‐term SatQKD option, including for daylight operation when appropriate filtering and pointing/turbulence mitigation are employed.