Quantum key distribution (QKD) via geostationary Earth orbit (GEO) satellites offers a compelling route to continuous, continental-scale secure communications. However, operation in this regime entails extreme channel loss and significant background noise, particularly if daylight operation is desired. We present a comprehensive end-to-end feasibility study of a decoy-state BB84 protocol in a GEO downlink configuration, incorporating variable-length finite-key security and tight statistical bounds to expand the achievable positive-key regime. Our analysis encompasses the principal receiver architectures relevant to downlink QKD and employs a physically realistic channel model that captures the dominant loss and noise mechanisms. We evaluate performance across rural, urban, and coastal environments at multiple wavelengths, including visible Fraunhofer absorption minima and the telecom band. Using historical cloud data across Europe, we forecast the annual secret-key yield across the continent. Through a systematic exploration of the high-dimensional parameter space, we identify key trade-offs and performance bottlenecks that determine feasibility. These results establish practical operating thresholds and provide actionable design guidelines for future GEO-QKD missions.
Quantum key distribution (QKD) via geostationary Earth orbit (GEO) satellites offers a compelling route to continuous, continental-scale secure communications. However, operation in this regime entails extreme channel loss and significant background noise, particularly if daylight operation is desired. We present a comprehensive end-to-end feasibility study of a decoy-state BB84 protocol in a GEO downlink configuration, incorporating variable-length finite-key security and tight statistical bounds to expand the achievable positive-key regime. Our analysis encompasses the principal receiver architectures relevant to downlink QKD and employs a physically realistic channel model that captures the dominant loss and noise mechanisms. We evaluate performance across rural, urban, and coastal environments at multiple wavelengths, including visible Fraunhofer absorption minima and the telecom band. Using historical cloud data across Europe, we forecast the annual secret-key yield across the continent. Through a systematic exploration of the high-dimensional parameter space, we identify key trade-offs and performance bottlenecks that determine feasibility. These results establish practical operating thresholds and provide actionable design guidelines for future GEO-QKD missions.
Establishing information-theoretically secure communication between arbitrary locations on Earth is a central goal of quantum networking, for which space-based distribution of quantum entanglement is a leading approach. Modelling and analysis of the performance of satellite entanglement pair distribution is therefore important for the architecture and design of future constellations and space systems. However, entanglement-based quantum key distribution in the absence of quantum repeaters, is especially prone to finite-key effects due to low coincident count rates compared to trusted-node single-path links. Quantifying these effects under realistic orbital conditions is therefore essential for the design of practical satellite quantum communication systems. Here, we develop a high-fidelity model of pair distribution from a low-Earth-orbit satellite that captures orbital dynamics, elevation-dependent loss, background noise, and extraneous detector effects. Integrating this with a finite-key security framework for the BBM92 protocol, we optimise the secret key length across different overpass geometries, orbital altitudes, and optical ground station (OGS) separations. We show that secure key generation remains feasible in early clear daytime conditions using baseline parameters representative of current technologies, while showing that modest system improvements could further extend daytime operation. Finally, we evaluate the annual secret key performance for representative intercity-scale OGS pairings. Our results provide quantitative performance bounds and practical design guidelines for near-term entanglement-based satellite QKD, enabling informed trade-offs between satellite payload complexity, ground infrastructure, and achievable secure key throughput.
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.
In this paper we analyze the feasibility of performing Quantum Key Distribution (QKD), in Earth-satellite up and downlinks and in intersatellite links, with two quantum cryptography protocols: BB84 and SARG04, and with two implementation options: with and without decoy states. As real measurements in these scenarios are not possible yet, the objective is to obtain results as realistic as possible to support the design of future satellite missions performing QKD. Therefore, we use realistic values for the optical hardware and take into account usual atmospheric conditions. In the same line, we assume specific types of attacks, namely the photon number splitting and the intercept-resend with unambiguous discrimination attacks, which could likely be the main threat to the first satellite-based QKD applications. A lower bound on the key generation rate of SARG04 with two decoy states is presented. The optimum signal- and decoy-states mean photon numbers for each protocol and each distance are also computed. The resulting values for the signal-state are larger than those often employed. We show that it may be possible to establish QKD with LEO (Low Earth Orbit) and, under certain circumstances, with MEO (Medium Earth Orbit) satellites, but not with GEO (Geostationary) ones. Furthermore, we obtain that the optimum signal-state mean photon number for SARG04 with two decoy states is almost independent of the link distance, which greatly facilitates its use in a real scenario.
In satellite-based quantum-key-distribution (QKD), the number of secret bits that can be generated in a single satellite pass over the ground station is severely restricted by the pass duration and the free-space optical channel loss. High channel loss may decrease the signal-to-noise ratio due to background noise, reduce the number of generated raw key bits, and increase the quantum bit error rate (QBER), all of which have detrimental effects on the output secret key length. Under finite-size security analysis, a higher QBER increases the minimum raw key length necessary for nonzero secret-key-length extraction due to less efficient reconciliation and postprocessing overheads. We show that recent developments in finite-key analysis allow three different small-satellite-based QKD projects, CQT-Sat, the United Kingdom QUARC-ROKS, and QEYSSat, to produce secret keys even under conditions of very high loss, improving on estimates based on previous finite-key bounds. This suggests that satellites in low Earth orbit can satisfy finite-size security requirements but that this remains challenging for satellites further from Earth. We analyze the performance of each mission to provide an informed route toward improving the performance of small-satellite QKD missions. We highlight the short- and long-term perspectives on the challenges and potential future developments in small-satellite-based QKD and quantum networks. In particular, we discuss some of the experimental and theoretical bottlenecks and the improvements necessary to achieve QKD and wider quantum networking capabilities in daylight and at different altitudes. Published by the American Physical Society 2024
Optical quantum communication utilizing satellite platforms has the potential to extend the reach of quantum key distribution (QKD) from terrestrial limits of ∼200 km to global scales. We have developed a thorough numerical simulation using realistic simulated orbits and incorporating the effects of pointing error, diffraction, atmosphere and telescope design, to obtain estimates of the loss and background noise which a satellite-based system would experience. Combining with quantum optics simulations of sources and detection, we determine the length of secure key for QKD, as well as entanglement visibility and achievable distances for fundamental experiments. We analyse the performance of a low Earth orbit satellite for downlink and uplink scenarios of the quantum optical signals. We argue that the advantages of locating the quantum source on the ground justify a greater scientific interest in an uplink as compared to a downlink. An uplink with a ground transmitter of at least 25 cm diameter and a 30 cm receiver telescope on the satellite could be used to successfully perform QKD multiple times per week with either an entangled photon source or with a weak coherent pulse source, as well as perform long-distance Bell tests and quantum teleportation. Our model helps to resolve important design considerations such as operating wavelength, type and specifications of sources and detectors, telescope designs, specific orbits and ground station locations, in view of anticipated overall system performance.
Abstract Establishing secure communication links at a global scale is a major potential application of quantum information science but also extremely challenging for the underlying technology. Although milestone experiments using satellite-to-ground links and exploiting singe-photon encoding for implementing quantum key distribution have shown recently that this goal is achievable, it is still necessary to further investigate practical solutions compatible with classical optical communication systems. Here, we examine the feasibility of establishing secret keys in a satellite-to-ground downlink configuration using continuous-variable encoding, which can be implemented using standard telecommunication components certified for space environment and able to operate at high symbol rates. Considering a realistic channel model and state-of-the-art technology, and exploiting an orbit subdivision technique for mitigating fluctuations in the transmission efficiency, we find positive secret key rates for a low-Earth-orbit scenario, whereas finite-size effects can be a limiting factor for higher orbits. Our analysis determines regions of values for important experimental parameters where secret key exchange is possible and can be used as a guideline for experimental efforts in this direction.