Entanglement distribution via free-space optical links. from high-altitude balloons to space-time cur-vature tests (QFREE)

Abstract

The QFREE project investigates the distribution of entangled photon pairs over free-space optical links using drones and stratospheric balloons, extending quantum communication beyond fibre-based networks. By integrating High-Altitude Platform Stations (HAPs) and precise optical tracking systems, QFREE contributes to a hybrid quantum communication system. The project also enables fundamental tests of quantum mechanics in curved space-time. A central outcome is a Swiss-Korean collaboration combining Swiss expertise in free-space quantum cryptography with Korean capabilities in optical tracking. FHNW develops a two-axis gimbal and optical fine-steering system (hardware and software) for balloon and drone platforms, laying the foundation for future satellite-based quantum networks.