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.
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.
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 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 With the goal of a space-based quantum network is to have satellites distribute keys between any nodes on the ground, we consider an evolved quantum network from a near-term form, in which a space-based relay, satellite executes a sequence of satellite-based quantum key distribution (SatQKD) missions, allowing any two ground nodes to have a shared secure key. Accordingly, we develop a comprehensive framework for the dynamic simulation of SatQKD and consider scheduling QKD downlink in future space-based quantum communication network. The embedding of precise orbital model including beam diffractions and atmosphere effects makes our framework more realistic. Incorporated with the local meteorological data to channel loss model, the cloud cover contribution to transmission disturbance is quantified to realize a quasi-experimental scenario. We provide a trade-off consideration between the duration available for communications and its corresponding average link loss during one orbit, which could be used to support decisions involving the locations of ground stations and the selection of the orbital parameters for a quantum satellite. Our work also shows that satellite downlink schedule could allow for the possibility to consider strategies for different SatQKD missions such as extending connection for distant ground nodes, prioritized delivery, or promoting keys utilization, which can be used as a guideline to support decisions for future satellite application.
Satellite-based quantum key distribution (QKD), leveraging low photon loss in free-space quantum communication, is widely regarded as one of the most promising directions to achieve global-scale QKD. With a constellation of satellites and a set of ground stations in a satellite-based QKD system, how to schedule satellites to achieve efficient QKD is an important problem. This problem has been studied in the dual-downlink architecture, where each satellite distributes pairs of entanglements to two ground stations simultaneously. However, it has not been studied in the single downlink architecture, where satellites create keys with each individual ground station, and then serve as trusted nodes to create keys between pairs of ground stations. While the single downlink architecture provides weaker security in that the satellites need to be trusted, it has many advantages, including the potential of achieving significantly higher key rates, and generating keys between pairs of ground stations that are far away from each other and cannot be served using the dual-downlink architecture. In this paper, we propose a novel opportunistic approach for satellite scheduling that accounts for fairness among the ground station pairs, while taking advantage of the dynamic satellite channels to maximize the system performance. We evaluate this approach in a wide range of settings and demonstrate that it provides the best tradeoffs in terms of total and minimum key rates across the ground station pairs. Our evaluation also highlights the importance of considering seasonal effects and cloud coverage in evaluating satellite-based QKD systems. In addition, we show different tradeoffs in global and regional QKD systems.
With the goal of a space-based quantum network is to have satellites distribute keys between any nodes on the ground, we consider an evolved quantum network from a near-term form, in which a space-based relay, satellite executes a sequence of satellite-based quantum key distribution (SatQKD) missions, allowing any two ground nodes to have a shared secure key. Accordingly, we develop a comprehensive framework for the dynamic simulation of SatQKD and consider scheduling QKD downlink in future space-based quantum communication network. The embedding of precise orbital model including beam diffractions and atmosphere effects makes our framework more realistic. Incorporated with the local meteorological data to channel loss model, the cloud cover contribution to transmission disturbance is quantified to realize a quasi-experimental scenario. We provide a trade-off consideration between the duration available for communications and its corresponding average link loss during one orbit, which could be used to support decisions involving the locations of ground stations and the selection of the orbital parameters for a quantum satellite. Our work also shows that satellite downlink schedule could allow for the possibility to consider strategies for different SatQKD missions such as extending connection for distant ground nodes, prioritized delivery, or promoting keys utilization, which can be used as a guideline to support decisions for future satellite application.