Kimia Mohammadi

We investigate feasible link architectures for transatlantic quantum entanglement distribution across a ground separation of approximately 6,500 km by comparing free-space scenarios involving satellites and High-Altitude Platforms (HAPs). By taking into account the optical link budget, radiation environment, orbital accessibility, and overall system complexity, including aperture requirements and payload constraints across both the space and ground segments, we identify a hybrid architecture consisting of a Low-Earth Orbit (LEO) satellite at 1,200 km altitude supported by two HAPs positioned above the quantum ground stations as a promising configuration. Our analysis shows that this architecture outperforms a conventional single-satellite scenario at higher orbital altitudes (~15,000 km). In addition to achieving improved performance, the satellite–HAP architecture offers practical advantages by reducing payload and launch complexity, while improving link availability through the maneuverability of HAPs under varying weather conditions. Overall, this hybrid configuration yields on the order of 5 X 10^6 secure key bits per year using 30 cm aperture ground receivers, nearly two orders of magnitude higher than achievable with a single MEO satellite and 1 m aperture ground receivers. These results demonstrate major benefits of hybrid satellite–HAP architectures by reducing system complexity while enabling scalable and more accessible quantum communication networks.