Abstract Global quantum communications will enable long-distance secure data transfer, networked distributed quantum information processing, and other entanglement-enabled technologies. Satellite quantum communication overcomes optical fibre range limitations, with the first realisations of satellite quantum key distribution (SatQKD) being rapidly developed. However, limited transmission times between satellite and ground station severely constrains the amount of secret key due to finite-block size effects. Here, we analyse these effects and the implications for system design and operation, utilising published results from the Micius satellite to construct an empirically-derived channel and system model for a trusted-node downlink employing efficient Bennett-Brassard 1984 (BB84) weak coherent pulse decoy states with optimised parameters. We quantify practical SatQKD performance limits and examine the effects of link efficiency, background light, source quality, and overpass geometries to estimate long-term key generation capacity. Our results may guide design and analysis of future missions, and establish performance benchmarks for both sources and detectors.
Abstract Global quantum communications will enable long-distance secure data transfer, networked distributed quantum information processing, and other entanglement-enabled technologies. Satellite quantum communication overcomes optical fibre range limitations, with the first realisations of satellite quantum key distribution (SatQKD) being rapidly developed. However, limited transmission times between satellite and ground station severely constrains the amount of secret key due to finite-block size effects. Here, we analyse these effects and the implications for system design and operation, utilising published results from the Micius satellite to construct an empirically-derived channel and system model for a trusted-node downlink employing efficient Bennett-Brassard 1984 (BB84) weak coherent pulse decoy states with optimised parameters. We quantify practical SatQKD performance limits and examine the effects of link efficiency, background light, source quality, and overpass geometries to estimate long-term key generation capacity. Our results may guide design and analysis of future missions, and establish performance benchmarks for both sources and detectors.
Abstract Global-scale quantum communication networks will require efficient long-distance distribution of quantum signals. While optical fibre communications are range-limited due to exponential losses in the absence of quantum memories and repeaters, satellites enable intercontinental quantum communications. However, the design of satellite quantum key distribution (SatQKD) systems has unique challenges over terrestrial networks. The typical approach to modelling SatQKD has been to estimate performances with a fully optimised protocol parameter space and with few payload and platform resource limitations. Here, we analyse how practical constraints affect the performance of SatQKD for the Bennett-Brassard 1984 (BB84) weak coherent pulse decoy state protocol with finite key size effects. We consider engineering limitations and trade-offs in mission design including limited in-orbit tunability, quantum random number generation rates and storage, and source intensity uncertainty. We quantify practical SatQKD performance limits to determine the long-term key generation capacity and provide performance benchmarks to support the design of upcoming missions.
Developing global quantum communication networks is integral to the realisation of the quantum internet, which is expected to impart a similar revolutionary impact on the technological landscape as the classical internet. Satellite-based quantum communications provides a practical route to global quantum networking. In this work, we model finite statistics to determine the finite secret key length generation in SatQKD systems that implement trusted-node downlink operation with weak coherent pulse sources. We optimise the finite key rate for different practical operations and determine the key generation footprints. Our work provides an essential guide for future satellite missions to establish performance benchmarks for both sources and detectors.
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.
Abstract Space-based entanglement distribution, as the backbone of the quantum Internet, is poised to enable global quantum networking from infrastructure to application platforms. Satellite-based quantum key distribution (SatQKD), with the entanglement-based QKD protocol of Bennett, Brassard, and Mermin (BBM92), promises source-independent security, but faces a trinity of scalability bottlenecks in dual-downlink configurations. Specifically, asymmetric link characteristics are exacerbated by optical ground station (OGS) pair system parameter differences, while orbit-dependent metrics, e.g., transmission window duration, overpass interval, and trajectory repeatability, introduce finite secret key length (SKL) extraction considerations. Further, quantum satellites will be within the range of multiple OGS pairs, which requires efficient scheduling of SatQKD to prioritize links, mitigate cloud cover disturbance, and maximize finite SKL. Here, we develop a co-modeling framework of dual-downlink SatQKD to support orbital parameter selection and performance comparison for asymmetric system-optics (e.g., aperture diameter, extraneous counts) parameters. We clarify the distinct performance of the SKL extraction methods for Sun-synchronous orbits (SSO) and polar orbits. We further incorporate the finite BBM92 SKL analysis into downlink scheduling optimisation to truncate adverse data collection periods and explore the advantages in flexibility and efficiency for global networking. Our work provides actionable design insights for future entanglement-based global quantum communications.
Space-based entanglement distribution, as the backbone of the quantum Internet, is poised to enable global quantum networking from infrastructure to application platforms. Satellite-based quantum key distribution (SatQKD), with the entanglement-based QKD protocol of Bennett, Brassard, and Mermin (BBM92), promises source-independent security, but faces a trinity of scalability bottlenecks in dual-downlink configurations. Specifically, asymmetric link characteristics are exacerbated by optical ground station (OGS) pair system parameter differences, while orbit-dependent metrics, e.g., transmission window duration, overpass interval, and trajectory repeatability, introduce finite secret key length (SKL) extraction considerations. Further, quantum satellites will be within the range of multiple OGS pairs, which requires efficient scheduling of SatQKD to prioritize links, mitigate cloud cover disturbance, and maximize finite SKL. Here, we develop a co-modeling framework of dual-downlink SatQKD to support orbital parameter selection and performance comparison for asymmetric system-optics (e.g., aperture diameter, extraneous counts) parameters. We clarify the distinct performance of the SKL extraction methods for Sun-synchronous orbits (SSO) and polar orbits. We further incorporate the finite BBM92 SKL analysis into downlink scheduling optimisation to truncate adverse data collection periods and explore the advantages in flexibility and efficiency for global networking. Our work provides actionable design insights for future entanglement-based global quantum communications.
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.