Real-time generation of quantum keys between satellite and ground nodes is essential for a scalable and global quantum network. We report the development of a QKD system that operate at gigahertz clock rate with multiplexed classical and quantum channels. This system is tested on a free-space link which is an emulation of the satellite to ground link with dynamic loss and random misalignments. With the assumption of a small satellite in low Earth orbit and a ground station with moderate aperture, we demonstrate the generation of >5 Mbits of quantum keys in a single emulated satellite pass.
Real-time generation of quantum keys between satellite and ground nodes is essential for a scalable and global quantum network. We report the development of a QKD system that operate at gigahertz clock rate with multiplexed classical and quantum channels. This system is tested on a free-space link which is an emulation of the satellite to ground link with dynamic loss and random misalignments. With the assumption of a small satellite in low Earth orbit and a ground station with moderate aperture, we demonstrate the generation of >5 Mbits of quantum keys in a single emulated satellite pass.
Satellite quantum key distribution (SatQKD) intermediated by a trusted satellite in a low-Earth orbit to ground stations along the satellite's path allows remote users to connect securely. To establish a secure connection, a SatQKD session must be conducted to each user over a dynamically changing free-space link, all within just a few hundred seconds. Because of the short time and large losses under which the QKD protocol will be implemented, it has not yet been possible to form a complete key by transmitting all the relevant information required within a single overpass of the satellite. Here, we demonstrate a real-time QKD system that is capable of forming a 4.58-megabit secure key between two nodes within an emulated satellite overpass. We anticipate that our system will set the stage for practical implementations of intercontinental quantum secure communications that can operate over large networks of nodes and enable the secure transmission of data globally.
This paper investigates the performance of free-space optics (FSO)-based satellite-assisted quantum key distribution (QKD). Specifically, we develop a simulation framework using the IBM Quantum Experience (IQX) simulator with Qiskit that closely emulates real-world QKD implementations. The low Earth orbit (LEO) satellite quantum channels, incorporating the atmospheric loss, atmospheric turbulence, and pointing misalignment, are taken into account. Using the developed framework, we investigate QKD performance, including quantum bit error rate (QBER) and secret key rate (SKR), by simulating the key generation rate by IQX, considering the impact of satellite quantum channels over SpaceX’s Starlink networks. The obtained results provide insights into the QKD performance under various quantum channel conditions in satellite-based FSO/QKD systems.
Quantum communication rates in terrestrial quantum networks are fundamentally limited by fiber loss, even in the presence of quantum repeaters. Satellites offer a solution for long-distance communication, with the most commonly explored scenario involving prepare-and-measure protocols connecting from orbit to a trusted-node ground station via free-space down-links. In contrast, up-link scenarios allow for entanglement to be distributed between a satellite and remote end-users in terrestrial networks, eliminating any trust requirement on the ground station. Here, we demonstrate an ultra-bright source of far-non-degenerate entangled photons and perform quantum key distribution in emulated high-loss satellite scenarios. With a loss profile corresponding to that of one of the pioneering Micius up-link experiments, and a terrestrial end-user separated by 10 km of telecom fiber, we achieve secure key bit accumulation of 5.2 kbit in a single emulated overpass in the asymptotic limit. Our results confirm the viability of upcoming low-Earth orbit receiver satellite missions.
Abstract Satellite-based quantum terminals are a feasible way to extend the reach of quantum communication protocols such as quantum key distribution (QKD) to the global scale. To that end, prior demonstrations have shown QKD transmissions from airborne platforms to receivers on ground, but none have shown QKD transmissions from ground to a moving aircraft, the latter scenario having simplicity and flexibility advantages for a hypothetical satellite. Here, we demonstrate QKD from a ground transmitter to a receiver prototype mounted on an airplane in flight. We have specifically designed our receiver prototype to consist of many components that are compatible with the environment and resource constraints of a satellite. Coupled with our relocatable ground station system, optical links with distances of 3–10 km were maintained and quantum signals transmitted while traversing angular rates similar to those observed of low-Earth-orbit satellites. For some passes of the aircraft over the ground station, links were established within 10 s of position data transmission, and with link times of a few minutes and received quantum bit error rates typically ≈3%–5% , we generated secure keys up to 868 kb in length. By successfully generating secure keys over several different pass configurations, we demonstrate the viability of technology that constitutes a quantum receiver satellite payload and provide a blueprint for future satellite missions to build upon.
Quantum repeaters and satellite-based free-space optical links are complementary technological approaches slated to overcome the exponential photon loss occurring in optical fibers and thus allow Quantum Key Distribution (QKD) at global scales. We analyse architectures where these approaches are combined and satellites are used as quantum repeater nodes to distribute entanglement to far-away optical ground stations. Here, we simulate dynamical, three-dimensional satellite-ground-station passes, going beyond previous investigations which typically consider static satellite links. Therefore, we numerically solve the equations of motion of the dynamic system consisting of three, low-Earth-orbit satellites separated in the along-track direction. The optical link model includes atmospheric attenuation, single mode fiber coupling, beam wandering and broadening, as well as adaptive optics effects. Analytical expressions for the Bell state measurement and associated error rates are derived for quantum memory assisted communications, accounting for exponentially decreasing retrieval efficiency and state coherence. We consider uplink and downlink architectures for continental and inter-continental connections and assess the influence of varying orbital elements on the expected. We also investigate alternative solutions for realising practically secure QKD networks in the near-term, whereby trusted nodes are only located in space and relatively inaccessible. By exploiting the newly introduced mode-pairing QKD protocol, we show that users located hundreds of kilometres from a ground station could establish a secure key with a satellite using well-established technologies and without requiring intermediate trusted nodes.
We investigate the feasibility of satellite-to-ground quantum key distribution (QKD) at multi-GHz clock rates, where secure key generation time is constrained, due to low-Earth orbit (LEO) satellite overpasses ( ≈ 300 s). Higher repetition rates offer a direct route to increased secure key rate (SKR), though system performance is fundamentally limited by detector timing jitter, optical coupling losses, and atmospheric turbulence, depending on receiver architecture. We combine finite-key modeling, detailed detector timing characterization, adaptive optics (AO) modeling, and real-time free-space QKD experiments at 1 GHz to evaluate practical receiver configurations based on multi-mode fiber-coupled avalanche photodiodes (MMF-APDs) and single-mode fiber-coupled superconducting nanowire single-photon detectors (SMF-SNSPDs), at projected rates >1 GHz. The results indicate clear operating regimes across a range of atmospheric conditions: MMF-APDs maximize secure key rates below ∼ 1 GHz, mainly due to their low coupling loss. However, low-jitter SMF-SNSPDs are required to obtain positive key rates at higher clock rates—with modeling and measured timing responses of our hardware indicating an estimated optimal operating point near ∼ 7.2 GHz—though AO correction is required for effective single-mode coupling under turbulence. The experimental and projected results provide quantitative performance bounds and realistic design targets for future high-rate satellite QKD systems, while highlighting the technological requirements needed to achieve end-to-end operation beyond the GHz regime.