Quantum key distribution (QKD) is critical for future proofed secure communication. Satellites will be necessary to mediate QKD on a global scale. The limitations of the existing quantum memory and repeater technology mean that twin-field QKD (TF-QKD) provides the most feasible near-term solution to perform QKD with an untrusted satellite. However, the TF-QKD requires links between ground stations and satellites to be phase stable. We show that phase stabilization of the links to LEO and MEO satellites is feasible in spite of phase noise due to atmospheric turbulence, laser instability, and path length asymmetry while only incurring a quantum bit error rate (QBER) penalty of less than 1.5%. These results are also applicable to future untrusted satellite networks employing precisely synchronized quantum memories or quantum repeaters.
Quantum key distribution (QKD) is critical for future proofed secure communication. Satellites will be necessary to mediate QKD on a global scale. The limitations of the existing quantum memory and repeater technology mean that twin-field QKD (TF-QKD) provides the most feasible near-term solution to perform QKD with an untrusted satellite. However, the TF-QKD requires links between ground stations and satellites to be phase stable. We show that phase stabilization of the links to LEO and MEO satellites is feasible in spite of phase noise due to atmospheric turbulence, laser instability, and path length asymmetry while only incurring a quantum bit error rate (QBER) penalty of less than 1.5%. These results are also applicable to future untrusted satellite networks employing precisely synchronized quantum memories or quantum repeaters.
Quantum key distribution (QKD) is a secure communication technique which uses quantum mechanics to protect communications. To overcome large distances, it requires the use of quantum repeaters, which are still challenging nevertheless feasible, or Twin-Field-QKD (TF-QKD) technology, which has been demonstrated several years ago. As it develops and matures, quantum technology is expected to play an increasingly major role in networks. Satellite QKD enables secure communication between devices via both satellites and ground stations. The study explores the transmission of quantum encryption technology in space and presents an overview of cubesats and satellites that currently use quantum key distribution (QKD) technology.
Abstract Twin-field quantum key distribution (TF-QKD) has attracted considerable attention in quantum communication for the extension of secure communication distance. In TF-QKD, precise photon phase control is required and has been realized using dual-band stabilization (DBS). In this study, we performed residual phase noise reduction in DBS using laser frequency stabilization. The achieved frequency stability of the light sources was better than 1 × 10 −12 when the averaging time is larger than 1 s, indicating that the laser frequency variation was less than 200 Hz at 1.5 μm. The integrated phase noise at 1 s was less than 200 mrad, and the corresponding quantum bit error rate at 1 s was less than 1% after applying laser frequency stabilization. This result demonstrates that the stringent phase stability requirements in TF-QKD can be achieved without relying on complex optical frequency combs, enabling a simpler and more cost-effective experimental setup.
This thesis aims to evaluate the feasibility of a global key distribution architecture without localizing the relay nodes entirely by investigating space geometry and a constraints-aware framework for satellite-based Twin-Field quantum key distribution (TF–QKD). The investigation concentrates on the inter-satellite link (ISL) and uplink (UL) segments in the context of realistic orbital dynamics. Under these conditions, the availability and quality of the link are jointly influenced by elevation, slant range, and line of sight. Geometric sizing of the Tx/Rx telescope apertures, Beer-Lambert atmospheric extinction, beam pointing instability, background scattering due to Sun/Moon radiation and synchronization penalties are all included in channel efficiency models, and they are all treated stochastically to reflect scalability with fidelity. XOR-based key forwarding is employed to evaluate end-to-end secure key generation on top of these physical layers. Path Routing and scheduling are guaranteed by graph based networks and numerical calculations. Various routing strategies are evaluated, such as key rate-aware optimization, distance weighed shortest path (KSP), and k-disjoint parallel chains. Performance across service-level metrics is quantified by simulation campaigns that span month-long orbital cycles, including delivered keys per pass, continuity curves, outage probability, time-to-key, throughput and k-disjoint availability. The findings indicate that the primary network design choices include uplink elevation and short, repeatable ISLs. By raising elevation masks and coordinating orbital phasing, narrow peaks in synchronous-key transmission are transformed into wide plateaus with a high secret key rate. The system maintained 12.3 Gbit/month of end-to-end keys under conservative XOR bottlenecks in the Sun-synchronous orbit (SSO) con stellation scenario that was demonstrated. It also accomplished median multi-path SKR in the tens of kbps with near-zero outages and provided three disjoint paths for virtually the entire run due to a calculated resource-intensive network. For a practical architectural candidate for global-scale quantum networks, these findings agree on satellite TF–QKD with XOR forwarding. The framework demonstrates how non-localized trust can be maintained without sacrificing continuity by utilizing orbital repeatability and impairment-aware scheduling. This work parallelize industry friendly post-quantum cryptography and advances the field of quantum communication.
Twin-field (TF) quantum key distribution (QKD) has rapidly risen as the most viable solution to long-distance secure fibre communication thanks to its fundamentally repeater-like rate-loss scaling. However, its implementation complexity, if not successfully addressed, could impede or even prevent its advance into real-world. To satisfy its requirement for twin-field coherence, all present setups adopted essentially a gigantic, resource-inefficient interferometer structure that lacks scalability that mature QKD systems provide with simplex quantum links. Here we introduce a technique that can stabilise an open channel without using a closed interferometer and has general applicability to phase-sensitive quantum communications. Using locally generated frequency combs to establish mutual coherence, we develop a simple and versatile TF-QKD setup that does not need service fibre and can operate over links of 100 km asymmetry. We confirm the setup's repeater-like behaviour and obtain a finite-size rate of 0.32 bit/s at a distance of 615.6 km.
Satellite-mediated quantum key distribution (QKD) is set to become a critical technology for quantum-secure communication over long distances. While satellite QKD cannot be effectively eavesdropped, we show it can be disrupted (or 'jammed') with relatively simple and readily available equipment. We developed an atmospheric attenuation and satellite optical scattering model to estimate the rate of excess noise photons that can be injected into a satellite QKD channel by an off-axis laser, and calculated the effect this added noise has on the quantum bit error rate. We show that a ground-based laser on the order of 1 kW can significantly disrupt modern satellite QKD systems due to photons scattering off the satellite being detected by the QKD receiver on the ground. This class of laser can be purchased commercially, meaning such a method of disruption could be a serious threat to effectively securing high-value communications via satellite QKD in the future. We also discuss these results in relation to likely future developments in satellite-mediated QKD systems, and countermeasures that can be taken against this, and related methods, of disruption.
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.