Advances in space quantum communications

Classical and quantum technologies have traditionally been viewed as orthogonal, with classical systems being deterministic and quantum systems inherently probabilistic. This distinction hinders the development of a scalable quantum internet even as the global internet continues expanding. We report a classical-decisive quantum internet architecture in which the integration of quantum information into advanced photonic technologies enables efficient entanglement distribution over a commercially deployed fiber network. On-chip precise synchronization between classical headers and quantum payloads enables dynamic routing and networking of high-fidelity entanglement guided by classical light. The quantum states are preserved through real-time error mitigation, relying solely on classical signal readout without disturbing quantum information. These classical-decisive features demonstrate a practical path to a scalable quantum internet using existing network infrastructure and operating systems.

The novel field of quantum technology is being promoted by academia, governments and industry. Quantum technologies offer new means for carrying out fast computation as well as secure communication, using primitives that exploit peculiar characteristics of quantum physics. While building quantum computing devices remains a challenge, the area of quantum communication and cryptography has been successful in reaching industrial applications. In particular, recently, plans for building quantum internet have been put into action and expected to be launched by 2020 in the Netherlands. Quantum internet uses quantum communication as well as quantum entanglement along with classical communication. This makes design of software platform for quantum networks very challenging and a daunting task. Seamless design and testing of platforms for quantum software, thus, becomes a necessity to develop complex simulators for this kind of networks. In this short paper, we argue that using coordination models such as Reo can significantly simplify the development of software applications for quantum internet. Moreover, formal verification of such quantum software becomes possible, thanks to the separation of concerns, compositionality, and reusability of Reo models. This paper introduces an extension of a recently developed simulator for quantum internet (SimulaQron) by incorporating Reo models extended with quantum data and operations, along with classical data. We explain the main concepts and our plan for implementing this extension as a new tool: SimulaQ(reo)n.

Teleporting energy to remote locations is new challenge for quantum information science and technology. Developing a method for transferring local energy in laboratory systems to remote locations will enable non‐trivial energy flows in quantum networks. From the perspective of quantum information engineering, we propose a method for distributing local energy to a large number of remote nodes using hyperbolic geometry. Hyperbolic networks are suitable for energy allocation in large quantum networks since the number of nodes grows exponentially. To realise long‐range quantum energy teleportation (QET), we propose a hybrid method of quantum state telepotation and QET. By transmitting local quantum information through quantum teleportation and performing conditional operations on that information, QET can theoretically be realized independent of geographical distance. The method we present will provide new insights into new applications of future large‐scale quantum networks and potential applications of quantum physics to information engineering.

Quantum technologies such as quantum sensing, quantum imaging, quantum communications, and quantum computing rely on the ability to actively manipulate the quantum state of light and matter. Quantum emitters, such as color centers trapped in solids, are a useful platform for the realization of elementary building blocks (qubits) of quantum information systems. In particular, the modular nature of such solid-state devices opens up the possibility to connect them into quantum networks and create nonclassical states of light shared among many qubits. The function of a quantum network relies on efficient and controllable interactions among individual qubits. In this context, we present a scheme where optically active qubits of differing excitation energies are mutually coupled via a dispersive interaction with a shared mode of an optical cavity. This generally off-resonant interaction is prohibitive of direct exchange of information among the qubits. However, we propose a scheme in which by acoustically modulating the qubit excitation energies it is, in fact, possible to tune to resonance a preselected pair of qubits and thus open a communication channel between them. This method potentially enables fast (approximately nanoseconds) and parallelizable on-demand control of a large number of physical qubits. We develop an analytical and a numerical theoretical model demonstrating this principle and suggest feasible experimental scenarios to test the theoretical predictions.

Quantum science and technology is a rapidly growing field that harnesses the unique properties of quantum mechanics. The manipulation of quantum systems has led to unprecedented development in secure quantum communication, simulation, computing, sensing and metrology. Despite the significance of these technologies, the existing literature lacks a comprehensive understanding of how they can address various challenges faced by Africa. We address this gap by using systematic literature review methods and draw insights from diverse perspectives to present an overview of the current state of quantum science and technology in Africa. Furthermore, we explore how the full adoption and implementation of quantum technologies can contribute to achieving the United Nations Sustainable Development Goals 1-4, 10, 13, and 17. We analyze the data from literature review and insights from African quantum experts, which we synthesize into a cohesive summary. This review underscores that, with appropriate efforts, quantum technologies can significantly promote social, economic, and environmental sustainability in Africa. This review goes beyond the present literature to offer a conceptual framework, theoretical insights and practical recommendations. This study is particularly timely, coinciding with the 2025 International Year of Quantum Science and Technology, which recognizes 100 years since the initial development of quantum mechanics.

There is an increasing need for Earth Observation (EO) missions to meet the information requirements in connection with Global Change Studies. Small and cost-effective missions are powerful tools to flexibly react on information requirements with space borne solutions. Small satellite missions can be conducted relatively quickly and inexpensively and provide increased opportunity for access to space. The spacecraft bus and instruments can be based either on optimised off-the-shelf systems, with little or no requirements for new technology, or on new high-technology systems. Thus a new class of advanced small satellites, including autonomously operating “intelligent” satellites may be created, opening new fields of application for scientific purposes as well as operational, public and commercial services. Further milestones in the small satellite Earth observation mission developments are the availability and improvement of small launchers, the development of small ground station networks connected with rapid and cost-effective data distribution methods, and cost-effective management and quality assurance procedures. Advantages of small satellite missions, complementing the large complex missions are: more frequent mission opportunities and therefore faster return of science and application data; larger variety of missions and therefore also greater diversification of potential users; more rapid expansion of the technical and/or scientific knowledge base; and greater involvement of local and small industry. The paper deals with general trends in the field of small satellite missions for Earth observation. Special attention is given to the potential of spatial, spectral, and temporal resolution of small satellite based systems. Examples show that constellations give the unique for small satellites possibility to provide good daily coverage of the globe or/and allow to observe dynamic phenomena.

We review the national projects on quantum information science and technology in Japan over the past 30 years. The main funding agencies for this field have been the Japan Science and Technology Agency, the National Institute of Information and Communications Technology, the Japan Society for the Promotion of Science, and the Cabinet Office of the Government of Japan. The total investment in the quantum information science and technology field from these funding agencies for the past 15 years amounts to US$250 million. A similar amount of investment has been put in parallel by industry. As a result, new science frontiers have been created, and some service prototypes, such as quantum key distribution systems and coherent Ising machines, have been delivered to user premises. Recently, Japan has launched new initiatives to advance quantum information science and technology to the next phase, and to make full use of them for the resolution of societal problems.

Because of the substantial advantages that small satellites can offer to educational programs on limited budgets, to those deploying global constellations in low Earth orbit, and to those who can meet specific space-related tasks with miniaturized payloads, it seems likely that there will continue to be an exponential increase in launch of small satellites and consequently, in the number of associated debris in orbit. In order to reduce space debris, national regulatory and technical solutions would need to be developed and implemented. In light of the fear of a future avalanche of space debris that can cascade out of control, there are many steps that are being taken to mitigate space debris and a number of these steps prescribe better ways to proceed with small satellite missions and experiments.

As a cost-effective and versatile solution, small satellites are increasingly being considered for space exploration. However, one of the major challenges in deploying small satellites for high total impulse missions, particularly deep space exploration, lies in the propulsion system. These missions face strict constraints in terms of volume, mass, and power budgets. This paper proposes a potential solution to this issue through the design of a bipropellant MEMS thruster. Simulation results indicate that this type of thruster offers superior performance compared to the monopropellant propulsion systems typically used in small satellite missions. Specifically, the bipropellant MEMS thruster demonstrates enhanced specific impulse and thrust-to-weight ratio, making it a promising alternative for small satellite propulsion in high total impulse missions.

Nowadays, everyone uses Internet, do financial transactions and many other day-to-day activities. As the users are becoming more and more aware of the privacy, data security had become a prime concern. Quantum Internet inspires to be a possible solution. Quantum Internet uses quantum key distribution to provide security by generating symmetric keys for the data transfer. Newly developed technologies and manufacturing processes paved way for designing and development of small satellites. Small satellites can be launched in forms of clusters at a marginal cost of launching large communication satellites. Here, we review the basic concepts of quantum key distribution. Its application in satellite communication specifically using CubeSat satellites. We also touch upon the recent development in the field of satellite-based QKD systems. A brief on the major milestones and important small satellite mission is also presented. Further, we present a comparison study between the prominent QKD algorithms pertaining to their application in satellite-based QKD systems. We conclude the article with discussion on the applications, advantages and disadvantages of using QKD on satellite-based communication networks, further extending it from local area networks to worldwide Internet.

Multi-partite entanglement is fundamental to emerging quantum technologies, such as quantum networks, which ultimately require devices with strong light–matter interactions and long coherence times. Here, we introduce nanobeam photonic crystal cavities combining both extreme quality factors (∼107) with sub-wavelength field confinement to reach unprecedented light–matter interactions. Operating at 780 nm, our devices are tailored for efficient coupling and entanglement with ultracold 87Rb atoms, a key ingredient in quantum networks due to their hyperfine structure. Our new designs also facilitate the precise optical trapping of atoms, and we demonstrate coherent entanglement generation between them, which is remarkably resilient to atomic displacements. These platforms can be easily scaled-up to extremely large quantum networks, for distributed quantum computing and future light-based quantum technologies.

With their ability to process and transfer quantum information, large-scale entanglement-based quantum networks could be at the heart of a new age of quantum information, enabling fundamentally new applications such as distributed quantum computation, quantum communication, and quantum enhanced sensing. Due to their long spin coherence, controllable local qubit registers and optically active spins, color centers in diamond are prime candidates for nodes of such a network, and have enabled some of the most advanced quantum network demonstrations to date. These demonstrations include the distribution of a 3-node GHZ state across a quantum network, entanglement swapping, entanglement distillation, and memory-enhanced quantum communication. To move beyond current proof-of-principle networks, a further increase of entanglement generation rates is crucial. This thesis presents theoretical and experimental work on enhancing the spin-photon interface of color centers in diamond to achieve this goal, making use of the Purcell effect. The discussed work follows two main directions: embedding of color centers in open, tuneable Fabry-Perot micro-cavities, and in all-diamond photonic crystal cavities. First, we describe theoretical and experimental progress towards cavity-enhanced quantum networks based on nitrogen-vacancy (NV) centers in diamond. Due to their first order sensitivity to electric fields, we choose to embed NV centers in microns-thin diamond membranes that can be integrated into open fiber-based micro-cavities. We develop analytical methods to optimize the design of such open cavity systems for maximum Purcell enhancement of embedded color centers. We demonstrate a method to fabricate optically coherent NV centers in microns-thin diamond membranes, and use such structures to demonstrate the resonant excitation and detection of coherent, Purcell enhanced NV emission. A theoretical model in excellent agreement with our results suggests our system can improve entanglement rates between distant NV centers by two orders of magnitude with near-term improvements to the setup. Second, we describe progress towards an efficient spin-photon interface of group-IV color centers in diamond by coupling them to photonic nanostructures, allowing for large-scale integration. Due to their first-order insensitivity to electric fields, group-IV color centers can be brought in close proximity to surfaces (~ 100 nm), allowing for sub-wavelength mode volumes and thus very high Purcell factors. We numerically optimize photonic crystal cavity designs to maximize the Purcell enhancement of embedded emitters, test the robustness of our designs to real-world fabrication imperfections, and devise a method to efficiently interface nanophotonic structures. We then proceed to fabricate all-diamond photonic crystal cavities, making use of a dry etching technique that is selective to different crystallographic directions, and characterize the resulting optical quality factors. Finally, we marry the developed fabrication methods to fabricate microns-sized diamond platelets that can be transferred from a holding frame in a controlled fashion. This capability could be crucial for the realization of hybrid photonic circuits that we expect to be at the heart of future large-scale quantum networks.

Quantum information technology has been developing rapidly in last two decades. Very recently, quite a few optical quantum key distribution networks have been reported, enabling preliminary practical applications in secure information transfer. Meanwhile, a number of significant progresses based on quantum network have also been made in the research of linear optical quantum computing, simulation and metrology. However, on the way towards large-scale optical quantum network serious problems occur. On the one hand, the distance of fiber-based quantum communication is limited, due to intrinsic fiber loss and decreasing of entanglement quality caused by the noisy environment. On the other hand, the probabilistic feature of single and entangled photon sources would also cause an exponentially increasing overhead for large-scale quantum network. To solve the above problems, quantum repeaters and/or transmission of optical quantum bits over free space channel can be efficiently exploited for future wide-area realization of quantum communication. In addition, memory built-in quantum repeaters would also enable scalable linear optical quantum computing, simulation and high precision measurement. In this talk I will present some recent experiments from our group, including eight-photon entanglement, topological quantum error-correction, quantum repeater and efficient and long-lived quantum memory, and entanglement distribution and quantum teleportation over 100km-scale free-space quantum channels. These experiments show the promising future possibility towards scalable quantum network with photons and atoms.

Currently, optical technology impacts most of our lives, from light used in scientific measurement to the fiber optic cables that makeup the backbone of the internet. However, as our current optical infrastructure grows, we discover that these technologies are not limitless. Astronomers find themselves unable resolve stars that are too close to one another. Meanwhile, the internet is always under threat as our computer technology improves and more complex ways to break encryption emerge, threatening our personal information and infrastructure. However, our current optical technology functions on classical principles, and can be easily improved by incorporating our knowledge of quantum optics. In order to implement quantum technologies, our understanding of quantum coherence must improve. Through this knowledge we can maintain quantum states, and therefore their information, longer. In this dissertation, I will demonstrate that with sufficient knowledge of coherent properties, a simple algebra can be derived which can provide rules for graph reductions on a quantum network graph. Using this knowledge, I then provide a rudimentary algorithm which can find the optimal subgraph for communication on a quantum network. Next, I demonstrate that by measuring the photon statistics and second-order quantum coherence of a field, one can create a neural network capable of distinguishing the light sources on a pixel. Which is then applied to develop an imaging scheme capable of surpassing the Abbe-Rayleigh Criterion. Lastly, I present a multiphoton quantum version of the van Cittert-Zernike theorem. This provides formalism capable of determining the propagation of quantum coherence throughout a system. I then demonstrate the usefulness of the theorem by demonstrating sub-Poissonian statistics created by a linear system with an incident thermal beam, obtainable only by post-selection. Altogether, this provides incite into new applications of coherence to quantum technologies and the formalism to extending our knowledge even further.

Quantum communications have progressed significantly, moving from a theoretical concept to small-scale experiments to recent metropolitan-scale demonstrations. As the technology matures, it is expected to revolutionize quantum computing in much the same way that classical networks revolutionized classical computing. Quantum communications will also enable breakthroughs in quantum sensing, metrology, and other areas. However, scalability has emerged as a major challenge, particularly in terms of the number and heterogeneity of nodes, the distances between nodes, the diversity of applications, and the scale of user demand. This paper describes InterQnet, a multidisciplinary project that advances scalable quantum communications through a comprehensive approach that improves devices, error handling, and network architecture. InterQnet has a two-pronged strategy to address scalability challenges: <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">InterQnet-Achieve</i> focuses on practical realizations of heterogeneous quantum networks by building and then integrating first-generation quantum repeaters with error mitigation schemes and centralized automated network control systems. The resulting system will enable quantum communications between two heterogeneous quantum platforms through a third type of platform operating as a repeater node. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">InterQnet-Scale</i> focuses on a systems study of architectural choices for scalable quantum networks by developing forward-looking models of quantum network devices, advanced error correction schemes, and entanglement protocols. Here we report our current progress toward achieving our scalability goals.