Gianluca De Santis

Future quantum networks depend entirely on the ability to distribute quantum resources \cite{kimble2008quantum, wehner2018quantum}. Although terrestrial optical fibers provide the foundation for such networks, fundamental attenuation limits their utility over intercontinental distances, making satellite-based links essential for global connectivity. A critical prerequisite for this infrastructure is the reliable distribution of entanglement, which enables information-theoretic secure communication via Quantum Key Distribution (QKD) and facilitates advanced protocols, such as entanglement routing via quantum repeaters. Historically, entanglement-based QKD has relied on bespoke, ad hoc experimental configurations tailored for proof-of-concept laboratory demonstrations \cite{rozenman2026free}. However, realizing an operational space-based quantum network necessitates transitioning from these specialized setups to robust, space-qualified hardware \cite{vergoossen2020spooqy}. Bridging the gap between terrestrial prototypes and orbital deployments requires the rigorous characterization of flight-representative payloads and automated optical ground stations under representative field conditions. Such a validation is vital to ensure the scalable distribution of quantum resources necessary for a global quantum internet. We deployed a horizontal free-space QKD experiment spanning a 1.8 km link in a semi-urban desert environment, effectively mimicking the architecture planned for future space-to-ground networks. The transmitter node integrated the space-qualified engineering model of the quantum light source and receiver designed for the upcoming SpeQtre satellite mission, functioning as a highly stable source of polarization-entangled photon pairs. At the receiver node, the experiment utilized the Abu Dhabi Quantum Optical Ground Station (ADQOGS) \cite{amairi2024versatile}, an automated facility engineered for free-space optical and quantum communications. The ADQOGS employs an 80 cm Ritchey–Chrétien telescope equipped with a precision acquisition and tracking system, single-photon detectors, and stringent spatial and spectral filtering stages optimized for background noise suppression. Together, this combination of a flight-ready transmitter and a highly specialized ground station creates a rigorous, real-world testbed for evaluating the performance of operational quantum hardware outside the laboratory. We report nighttime operations under stable atmospheric conditions. The integrated system demonstrated sustained operational stability, yielding a sifted coincidence rate of approximately 24,000 photon pairs per second. We recorded a mean quantum bit error rate (QBER) of 4.78\% and extracted a finite-size secure key rate of 7565 bps, validating the efficacy of the entanglement-based link. Furthermore, extrapolating these metrics to a realistic Low Earth Orbit (LEO) scenario indicates that the hardware can successfully overcome the substantial diffraction and atmospheric losses expected during a LEO satellite downlink. Ultimately, the successful field integration of a flight-representative payload with an automated ground station verifies the operational readiness of the hardware. These results mark a decisive step toward the execution of the SpeQtre mission and provide critical empirical foundations for the deployment of large-scale, satellite-based quantum communication networks.

Quantum communication protocols, offering information-theoretic security, position satellite-based quantum key distribution (QKD) as a pivotal enabler for secure global communication networks. To ensure practical utility for end-users, the placement of optical ground stations (OGSs) must be strategically determined based on the topology of terrestrial quantum networks. Importantly, the site selection criteria recognize that free-space channels, unlike astronomical sites, are not optimized for such applications. Therefore, a comprehensive characterization of free-space channels in diverse environments is essential for designing and implementing a robust global quantum network. In this study, we present a measurement-based characterization of the atmospheric channel at the Abu Dhabi Quantum Optical Ground Station (ADQOGS). Two complementary experimental setups were employed: a ground-based weather station, which continuously monitors key atmospheric parameters, and a quantum acquisition and tracking system that integrates single-photon detectors, mounted on an RC telescope. These setups enable the simultaneous acquisition of classical and quantum signals, both of which are critical for assessing satellite QKD links. We report the experimental results acquired at the ADQOGS site, focusing on key atmospheric parameters impacting satellite-ground quantum communication. Specifically, we show measurements of atmospheric turbulence and background light. The results were analyzed to evaluate their impact on link availability and overall QKD performance in different scenarios. Our findings offer valuable insights for optimizing satellite-ground quantum links, enhancing link stability, and informing the design of future large-scale quantum-secure communication networks. This work contributes to the ongoing efforts toward establishing a robust global quantum communication infrastructure.

We present the Abu Dhabi Quantum Optical Ground Station (ADQOGS), a versatile optical ground station designed for diverse satellite-based quantum key distribution (QKD) missions. As the first of its kind in the Middle East, ADQOGS’s primary goal is to connect the UAE to global quantum-secured communication networks, thus overcoming the limited reach of terrestrial, fiber-based, QKD lines. The ability of the station to accommodate the reception and emission of multiwavelength optical signals promotes the diversification of space-based trusted nodes and allows a novel parallel trusted node approach to space QKD.

Quantum key distribution (QKD) via satellite links is the only currently viable solution to create quantum-backed secure communication at a global scale. To achieve intercontinental coverage with available technology one must adopt a “flying trusted node” paradigm, in which users fully trust the satellite platform. The major part of the poster will focus on our latest work where inspired by the concept of distributed secret sharing and the imminent projected launch of several QKD-equipped satellites, we proposed a parallel trusted node approach, in which key distribution is mediated by several satellites in parallel. This distributes the trust, removes single points of failure, and reduces the necessary assumptions. In addition, we discussed the versatility that an optical ground station should provide to execute such a protocol and, in general, to be fully integrated into a multi-party global quantum network. Finally, one last section of the poster will focus on how we will implement the idea of versatility and adaptability at the Abu Dhabi Quantum Optical Ground Station from a hardware perspective.