Propagating quantum microwaves: towards applications in communication and sensing
Mateo Casariego, Emmanuel Zambrini Cruzeiro, Stefano Gherardini, Tasio Gonzalez-Raya, Rui André, Gonçalo Frazão, Giacomo Catto, Mikko Möttönen, Debopam Datta, Klaara Viisanen, Joonas Govenius, Mika Prunnila, Kimmo Tuominen, Maximilian Reichert, Michael Renger, Kirill G. Fedorov, Frank Deppe, Harriet van der Vliet, A J Matthews, Yolanda Fernández, Réouven Assouly, Rémy Dassonneville, Benjamin Huard, Mikel Sanz, Yasser Omar
Abstract The field of propagating quantum microwaves is a relatively new area of research that is receiving increased attention due to its promising technological applications, both in communication and sensing. While formally similar to quantum optics, some key elements required by the aim of having a controllable quantum microwave interface are still on an early stage of development. Here, we argue where and why a fully operative toolbox for propagating quantum microwaves will be needed, pointing to novel directions of research along the way: from microwave quantum key distribution to quantum radar, bath-system learning, or direct dark matter detection. The article therefore functions both as a review of the state-of-the-art, and as an illustration of the wide reach of applications the future of quantum microwaves will open.
Abstract The field of propagating quantum microwaves is a relatively new area of research that is receiving increased attention due to its promising technological applications, both in communication and sensing. While formally similar to quantum optics, some key elements required by the aim of having a controllable quantum microwave interface are still on an early stage of development. Here, we argue where and why a fully operative toolbox for propagating quantum microwaves will be needed, pointing to novel directions of research along the way: from microwave quantum key distribution to quantum radar, bath-system learning, or direct dark matter detection. The article therefore functions both as a review of the state-of-the-art, and as an illustration of the wide reach of applications the future of quantum microwaves will open.
The thesis establishes a link between theoretical foundations and practical applications in the emerging field of propagating quantum microwaves. Although the concrete focus of the main results lies in specific quantum communication and sensing protocols, the thesis also gives a self-contained introduction to quantum parameter estimation and Gaussian quantum continuous variables, justifying the theoretical results used. Motivated, firstly, by the compatibility between superconducting circuits (a promising quantum computing platform), and the microwave frequency range; and, secondly, by the transparency window of the atmosphere to these frequencies, the work contains two concrete contributions to the fields of microwave quantum sensing and communication: a novel protocol that uses frequency entanglement to measure the first order dependence in frequency of the reflectivity of an object; and a large investigation on different aspects of entanglement degradation due to loss and atmospheric absorption in the context of continuous-variable entanglement distribution for the task of quantum teleportation in open-air. The dissertation includes, as a last chapter, an article that reviews the state-of-the-art in quantum microwave technology, and proposes different research lines, including quantum communication between Earth-based stations and satellites, quantum radar, direct dark matter detection, and exploration of the quantum properties of the cosmic microwave background. This more speculative, yet rigorous chapter closes with a roadmap for possible future research lines in the field of propagating quantum microwaves, that can serve as an outlook of the thesis.
Quantum communications has emerged as an important paradigm for achieving secure fast communications. Significant technological breakthroughs have been achieved in this area over the years using quantum optics. In contrast, quantum microwaves are recently beginning to receive increased attention, due in part to the potential for an easier integration with current microwave communications infrastructure. This paper explores the generation, propagation and detection of quantum microwaves as processes required for open-air communication. It presents a brief description of the theory and provides a summary of recent progress in these operations. The paper ends by highlighting challenges regarding the practical realization of this technology.
By combing photonics and radiofrequency (RF) engineering, microwave photonics has been widely studied in the past few decades for the generation, processing, control and distribution of microwave and RF signals using photonic techniques. In parallel with the continuous hot research on classic microwave photonic systems, cross research between microwave photonics and other disciplines is also a promising research spot for scientists in this area. Here we review emerging advances in recent years in cross research between microwave photonics and quantum technology, i.e., quantum microwave photonics that harnessing quantum technology to achieve features or functions that are very complex or even not possible using traditional microwave photonic technology and vice versa. Key motivations of quantum microwave photonics are discussed. The basic operation principle of the quantum single-photon detection scheme, which is the main building block of current quantum microwave photonic systems, is provided. Selected recent advances, including weak microwave signal detection, microwave photonic phase shifting and filtering, nonlocal frequency-to-time mapping, RF compressed sensing, and quantum key distribution, are summarized. Challenges and future prospects of quantum microwave photonics are also discussed.
Quantum communication has attracted much attention in recent years, provides an ultimate level of security, and uniquely it is one of the most likely practical quantum technologies at present. In order to realize global coverage of quantum communication networks, not only need the help of satellite to realize wide area quantum communication, need implementation of optical fiber system to realize city to city quantum communication, but also, it is necessary to implement end-to-end quantum communications intercity and wireless quantum communications that can be received by handheld devices. Because of the limitation of application of light in buildings, it needs quantum communication with microwave band to achieve quantum reception of wireless handheld devices. The single microwave photon energy is very low, it is difficult to directly detect, which become a difficulty in microwave quantum detection. This paper summarizes the mode of single microwave photon detection methods and the possibility of application in microwave quantum communication, and promotes the development of quantum communication in microwave band and quantum radar.
Quantum communication is a holy grail to achieve secure communication among a set of partners, since it is provably unbreakable by physical laws. Quantum sensing employs quantum entanglement as an extra resource to determine parameters by either using less resources or attaining a precision unachievable in classical protocols. A paradigmatic example is the quantum radar, which allows one to detect an object without being detected oneself, by making use of the additional asset provided by quantum entanglement to reduce the intensity of the signal. In the optical regime, impressive technological advances have been reached in the last years, such as the first quantum communication between ground and satellites, as well as the first proof-of-principle experiments in quantum sensing. The development of microwave quantum technologies turned out, nonetheless, to be more challenging. Here, we will discuss the challenges regarding the use of microwaves for quantum communication and sensing. Based on this analysis, we propose a roadmap to achieve real-life applications in these fields.
This paper provides a detailed exploration of quantum radar technology, focusing on the generation, measurement, and theoretical analysis of quantum-correlated signals in both optical and microwave domains. We examine the mechanisms behind producing entangled signals and their application to improve radar sensitivity and accuracy in noisy environments. A review of key studies is presented, with emphasis on their experimental setups and the limitations that define the potential of quantum radar. By aggregating data on object detection range and analyzing global research trends through visualizations, including a bar chart and a world map, we illustrate the growing interest and research efforts in this domain. Our findings highlight the significant advancements and remaining challenges in developing practical quantum radar systems, as well as the worldwide collaboration driving progress in this cutting-edge field.