Future global connectivity demands necessitate space-terrestrial integrated networks (STINs), where high-speed laser communication forms the backbone of inter-satellite and satellite-ground links as well as the ground backbone network. Concurrently, the inherent openness of STINs requires physical layer security, which can be addressed by continuous-variable quantum key distribution (CV-QKD) based on laser coherent states for its high key rates and compatibility to existing laser communication infrastructures. Both classical laser communication performance and CV-QKD security are fundamentally limited by the standard quantum limit (SQL) of homodyne detection. This paper mainly focuses the vital roles and functions of quantum receivers in overcoming the SQL to enhance network capacity of future STINs. We first outline the development history of quantum receivers, highlighting displacement receivers as a promising solution. Then displacement receivers for both coherent communications and incoherent communications are introduced. At last, we identify the major challenges and potential breakthrough directions for implementing quantum receivers in future STINs.
Future global connectivity demands necessitate space-terrestrial integrated networks (STINs), where high-speed laser communication forms the backbone of inter-satellite and satellite-ground links as well as the ground backbone network. Concurrently, the inherent openness of STINs requires physical layer security, which can be addressed by continuous-variable quantum key distribution (CV-QKD) based on laser coherent states for its high key rates and compatibility to existing laser communication infrastructures. Both classical laser communication performance and CV-QKD security are fundamentally limited by the standard quantum limit (SQL) of homodyne detection. This paper mainly focuses the vital roles and functions of quantum receivers in overcoming the SQL to enhance network capacity of future STINs. We first outline the development history of quantum receivers, highlighting displacement receivers as a promising solution. Then displacement receivers for both coherent communications and incoherent communications are introduced. At last, we identify the major challenges and potential breakthrough directions for implementing quantum receivers in future STINs.
Losses and attenuation are the main limitations to implementing secure quantum networks based on fiber or free-space optical links over long distances. A hybrid satellite–ground approach offers an effective solution to overcome these constraints and achieve higher key transmission rates. This article presents a systematic review of publications on satellite quantum communication, providing an overview of quantum key distribution with satellites, the use of satellite networks with emphasis on commonly adopted orbits, and the role of satellites in such architectures. Special attention is given to the implementation of continuous-variable QKD (CV-QKD) in satellite-based channels, highlighting its challenges and potential for integration into future satellite-based quantum networks.
Satellite-based quantum communications represent a critical advancement in the pursuit of secure, global-scale quantum networks. Leveraging the principles of quantum mechanics, these systems offer unparalleled security through Quantum Key Distribution (QKD) and other quantum communication protocols. This review provides a comprehensive overview of the current state of satellite-based quantum communications, focusing on the evolution from terrestrial to space-based systems. We explore the distinct advantages and challenges of discrete-variable (DV) and continuous-variable (CV) quantum communication technologies in the context of satellite deployments. The paper also discusses key milestones such as the successful implementation of quantum communication via the Micius satellite and outlines the primary challenges, including atmospheric turbulence and the development of quantum repeaters, that must be addressed to achieve a global quantum internet. This review aims to consolidate recent advancements in the field, providing insights and perspectives on the future directions and potential innovations that will drive the continued evolution of satellite-based quantum communications.
Continuous variable quantum key distribution (CVQKD) uses the continuous quadratures of light to share a secret key between a transmitter and receiver. The presence of an eavesdropper can be detected by fundamental quantum mechanics. Compared to the more established discrete variable QKD, CVQKD uses more cost-effective homodyne detectors which are more compatible with current telecommunication technologies. In a future global quantum network, CVQKD could be used to ensure the secure exchange of information. In this work, the feasibility of a variety of CVQKD protocols in different channels that could be used to establish a global quantum network are studied. These are the Gaussian modulated and discrete modulated CVQKD protocols for satellite to optical ground station downlinks and uplinks for Earth-space connections, inter-satellite links for space connections, satellite to ship and underwater links for maritime connections, and fibre network links for terrestrial connections. Secret key distribution between continents and various regions is simulated while accounting for the different adverse effects associated with each link. The combination of these connections with routing and scheduling ensures inter-continental high-speed information exchange with unconditional security that is required to achieve the goal of a global quantum network.
Satellite quantum communications have received a surge of interest in recent years, encouraged by the success of the QUESS experiments and as a reaction to advances in quantum computing. This work focuses on low Earth orbit nanosatellite missions, which offer several benefits (e.g. lower costs, greater launch availability, easier to replenish) over satellites at different orbit heights (medium Earth orbit, geosynchronous Earth orbit) and satellite size classes (e.g. small-sats, etc). Recent work on low Earth orbit satellite Quantum Key Distribution (QKD) has focused on transmitters and quantum sources, with less attention paid to the receiver side of the link. This review addresses that imbalance by focusing on the receiver and detection systems of satellite quantum communications. This work has found that two-way beacon acquisition and tracking systems are both a common element of state-of-the-art missions, and likely to remain a critical subsystem to ensure high-quality satellite-to-ground station links; however, improvements to detection and tracking algorithms could be made. For discrete variable QKD, receivers and detection systems in nanosatellites at low Earth orbit are likely to remain using silicon single photon avalanche diodes, while receivers and detection systems in optical ground stations may opt for superconducting nanowire single photon detectors, as cryogenic cooling is feasible. For continuous variable QKD, the receivers and detection systems, using coherent detection systems, share many hardware elements with classical optical satellite communications. Combined with coherent detection systems’ inherent resilience to operating during daytime conditions, this makes continuous variable QKD an attractive prospect for future missions, if its fundamental challenges can be overcome.
Satellite-based quantum networks are emerging as a promising solution for the development of a global quantum internet in the near future. The ability to leverage the advantageous lower attenuation of optical signals from satellites to ground presents an exciting opportunity to establish a robust and secure quantum communication infrastructure on a global scale. By utilizing a constellation of satellites, it becomes feasible to continuously distribute high-fidelity quantum entanglements among ground stations over long distances, overcoming the limitations of traditional terrestrial-based quantum communication systems. In this article, we first provide a brief survey of existing solutions for satellite-based entanglement distribution, highlighting the various approaches and technologies that have been employed in this rapidly evolving field. We then delve into a formulated optimal entanglement distribution problem, aiming to optimize the distribution of quantum entanglement resources across the satellite network to maximize efficiency and reliability. This problem is addressed through a detailed exploration of several different methodologies and algorithms, each tailored to specific operational settings and constraints. Our experimental results confirm the efficiency of these approaches and provide valuable insights into their practical implementation and performance. Finally, we identify several key directions for further study and development in the realm of satellite-based quantum networks.
Quantum Key Distribution (QKD) offers a revolutionary method for achieving information-theoretic security in communication systems by leveraging quantum mechanical principles. With foundational protocols like BB84 and newer innovations such as phase-matching and device-independent QKD, the field has rapidly progressed from theoretical constructs to real-world prototypes. Recent advancements in integrated photonics, high-speed key generation, and satellite-based systems suggest a transformative potential for global cybersecurity infrastructure. However, significant challenges remain in extending secure communication distances, ensuring practical implementation security, reducing cost and size of components, and integrating QKD into existing network architectures. This paper reviews the state-of-the-art in QKD, discusses emerging trends such as chip-based and layered QKD systems, evaluates satellite and free-space deployments, and examines the practical limitations and solutions for long-distance and high-rate secure communications. It concludes by highlighting future directions including standardization, hybrid classical-quantum infrastructures, and software-defined QKD networks.