The rapid development of the digital era and the increasing demands of information technologies create a need to create more reliable, secure and efficient communication systems. In this context, quantum signals represent a technology of the future that responds to the challenges that classical signal systems can no longer cope with — for example, the highest level of information security, accuracy and transmission speed. The use of quantum entanglement, superposition and correlations makes it possible to protect and process information at the highest level. Accordingly, the implementation of quantum signals is critically important for areas such as quantum communication, secure cyberinfrastructure, high-tech sensors and quantum computing systems. The paper reviews the role of quantum signals in modern technologies and their potential in the near future. Quantum signal theory combines the principles of quantum physics, information theory and signal processing. These features provide the highest accuracy in information transmission and processing, which is especially important in the development of quantum communication, quantum radars, and quantum sensors. This paper reviews the theoretical foundations of quantum signals, basic models, and their potential applications in modern technologies.

Advantage of quantum radar with intensity fluctuations

Squeezed light, a prominent non-classical state of light, exhibits reduced quantum noise in one quadrature component below the standard quantum limit (SQL). The property enables quantum-enhanced precision measurements, surpassing the SQL in quantum sensing applications. This review comprehensively introduces the fundamental concepts, classifications, and experimental generation techniques of squeezed light. It further explores its pivotal role and recent advances in diverse quantum sensing domains, including interferometry, gravitational wave detection, magnetometry, force sensing, biomedical sensing, and quantum radar. The review covers theoretical foundations of squeezed states (including quadrature operators and classification schemes, experimental generation techniques in atomic ensembles, nonlinear crystals, and fibers), fundamentals of quantum sensing with squeezed light (from quantum noise theory to quantum-enhanced metrology), and quantum-enhanced sensing applications across the aforementioned domains. Finally, future challenges and opportunities in the field are discussed.

Abstract With the continuous advancement of quantum radar technology, the detection capabilities for stealth aircraft have been significantly enhanced, posing an increasingly substantial threat to such targets. Consequently, it has become imperative to investigate the design and optimization of quantum radar stealth for aircraft. This paper proposes a novel quantum radar stealth optimization method specifically tailored for flying wing aircraft. Initially, based on the definition of QRCS (Quantum Radar Cross Section) and the surface element transformation of complex three-dimensional targets, a QRCS calculation method suitable for flying wing aircraft is derived. Subsequently, a quantum stealth optimization system for flying wing aircraft is developed based on this methodology. Through the research on the quantum stealth optimization of flying wing aircraft, the optimal quantum stealth configuration is obtained.

The engineering applications of quantum mechanics have seen both successes (mainly in metrology and sensing) and failures. Failures, generally full of teachings, deserve some analysis. A significant failure case is that of quantum radar (QR), studied for over 15 years, with some hundred publications produced, but with neither real-word applications nor operational results. In the QR case, even before the experimental phase, simple evaluations indicate the lack of effectiveness in all practical applications. This “negative” result (in Karl Popper’s falsification theory meaning) was ignored, or censored, for a relatively long period, which may be explained by (i) a not-adequate self-evaluation process, (ii) Pareto’s analysis of belief, and (iii) some researchers’ networking.

Quantum two-mode squeezed (QTMS) radar, inspired by quantum illumination but without joint measurements in the receiver, has shown promise in target detection. However, the current prototype of quantum radar, using full-microwave superconducting components, faces challenges in achieving long-range performance. In this study, we propose the integration of an array of Josephson parametric amplifiers (JPAs) in a dilution refrigerator to enhance the performance of QTMS quantum radar. Through the evaluation of signal-to-noise ratio (SNR) and receiver operating characteristic (ROC) metrics, we demonstrate the effectiveness of this enhancing strategy. Our results indicate that the presence of an array of two JPAs significantly improves both the SNR and the detection probability compared to a single JPA configuration, thereby boosting the overall performance of QTMS radar. The key factor of this improvement is the cross-correlation between JPAs, which has a notable impact on the analytical outcomes of the quantum radar. This research provides valuable insights to engineers who want to optimize the design of advanced quantum QTMS radar systems.

Enhancing the performance of quantum radar with zero-photon subtraction

PurposeThe purpose of this paper is to provide details of developments in quantum technologies and consider their potential applications in robotics.Design/methodology/approachFollowing a short introduction, this study first provides an overview of the global quantum technology landscape. It then discusses developments in quantum computing and sensing technologies. Potential applications in robotics are then considered and finally, brief conclusions are drawn.FindingsQuantum technologies are the topic of a rapidly growing global R&D effort. Quantum computing has the potential to conduct conventional computations far more rapidly than traditional computers and solve complex problems that are presently challenging or impossible. If realised, robotic applications could include enhanced route planning, machine learning and data fusion. Quantum position and magnetic field sensors have the potential to revolutionise navigation systems in airborne, land and marine robots and overcome limitations of GPS and inertial measurement units. Magnetic sensors also have a role in health care in the control of robotic prostheses and exoskeletons and in brain–computer interface techniques. Quantum radar, lidar and imaging systems stand to outperform their conventional counterparts, and applications are anticipated in military and civilian robots. Quantum technologies are still at an early stage of development, and much progress will be made in the future, opening up many further robotic applications.Originality/valueThis study provides an insight into quantum technology developments and their potential applications in robotics.

A Note on the Efficient Operation of Quantum Radar and the Fair Classical Comparison

The entangled quantum radar applies the quantum information technology to the radar sensing network and detection system. The dynamic particle changes and optical attenuation caused by complex atmospheric environments will severely limit the traditional radar performance. Due to entanglement characteristics, the entangled optical quantum radar has better anti-stealth interference ability, stronger anti-turbulence properties, and higher spatial resolution which makes it promising in complex and high-attenuation environments. In addition, quantum radar based on the entangled light source can overcome the limitations of low imaging resolution and low confidentiality in traditional target detection. Therefore, high-precision positioning and high-resolution imaging are the research focus of the quantum radar sensing network. Based on this, we first design and optimize an optical path structure of the quantum entangled light source to obtain higher brightness entangled source which is suitable for complex atmospheric environments. Second, in response to the problem of low positioning accuracy in the traditional quantum radar, we design a new positioning optical path and propose a novel entangled optical quantum positioning method based on the photon scattering model. Third, to address the problems of low resolution and slow speed in traditional quantum radar imaging, we propose a new entangled light quantum imaging method based on two-phase coincidence counting. Finally, we conduct extensive experiments to evaluate the effectiveness of the proposed method in complex atmospheric environments and further provide possibilities for the entangled light source quantum radar sensing network.

Corrections to “Engineering Constraints and Application Regimes of Quantum Radar”

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.

Quantum sensing promises to revolutionize sensing applications by employing quantum states of light or matter as sensing probes. Photons are the clear choice as quantum probes for remote sensing because they can travel to and interact with a distant target. Existing schemes are mainly based on the quantum illumination framework, which requires quantum memory to store a single photon of an initially entangled pair until its twin reflects off a target and returns for final correlation measurements. Existing demonstrations are limited to tabletop experiments, and expanding the sensing range faces various roadblocks, including long-time quantum storage and photon loss and noise when transmitting quantum signals over long distances. We propose a novel quantum sensing framework that addresses these challenges using quantum frequency combs with path identity for remote sensing of signatures (“qCOMBPASS”). The combination of one key quantum phenomenon and two quantum resources—namely, quantum-induced coherence by path identity, quantum frequency combs, and two-mode squeezed light—allows for quantum remote sensing without requiring quantum memory. The proposed scheme is akin to a quantum radar based on entangled frequency-comb pairs that uses path identity to detect, range, or sense a remote target of interest by measuring pulses of one comb in the pair that never traveled to the target but that contains target information “teleported” by quantum-induced coherence by path identity from the other comb in the pair that traveled to the target but is not detected. We develop the basic qCOMBPASS theory, analyze the properties of the qCOMBPASS transceiver, and introduce the qCOMBPASS equation—a quantum analog of the well-known LIDAR equation in classical remote sensing. We also describe an experimental scheme to demonstrate the concept using two-mode squeezed quantum combs. qCOMBPASS can strongly impact various applications in remote quantum sensing, imaging, metrology, and communications. These applications include detection and ranging of low-reflectivity objects, measurement of small displacements of a remote target with precision beyond the standard quantum limit (SQL), standoff hyperspectral quantum imaging, discreet surveillance from space with low detection probability (detect without being detected), very-long-baseline interferometry, quantum Doppler sensing, quantum clock synchronization, and networks of distributed quantum sensors. Published by the American Physical Society 2024

Abstract The authors consider a quantum radar which operates on the quantum illumination principle. The authors’ attention is focused on its function of target detection in a noisy environment. The role of the optical parametric amplifier (OPA) in detection is first examined by the authors, and a dual‐OPA design for more flexible combination of optimised gains is proposed, resulting in a detector substantially improved in its performance from the normally used 1‐OPA design. Then, the use of the entanglement information in the covariance matrix (CM) between the returned signal and idler beams for detection is considered, and a technique to extract such information is proposed. By employing some statistical relationships between positive definite matrices, the authors come up with a new target detection method. Numerical experiments confirm the superior detection performance of the CM detectors compared to that of the OPA detectors.

This work, written for engineers or managers with no special knowledge of quantum mechanics, nor deep experience in radar, aims to help the scientific, industrial, and governmental community to better understand the basic limitations of proposed microwave quantum radar (QR) technologies and systems. Detection and ranging capabilities for QR are critically discussed and a comparison with its closest classical radar (CR), i.e., the noise radar (NR), is presented. In particular, it is investigated whether a future fielded and operating QR system might really outperform an “equivalent” classical radar, or not. The main result of this work, coherently with the recent literature, is that the maximum range of a QR for typical aircraft targets is intrinsically limited to less than one km, and in most cases to some tens of meters. Detailed computations show that the detection performance of all the proposed QR types are orders of magnitude below the ones of any much simpler and cheaper equivalent “classical” radar set, in particular of the noise radar type. These limitations do not apply to very-short-range microwave applications, such as microwave tomography and radar monitoring of heart and breathing activity of people (where other figures, such as cost, size, weight, and power, shall be taken into account). Moreover, quantum sensing at much higher frequencies (optical and beyond) is not considered here.

The 2024 3rd International Conference on Electronics and Integrated Circuit Technology (EICT 2024) took place in Nanchang, China from April 12th to 14th, 2024 via virtual form. The main goal was to bring together scientists, researchers and developers engaged in fields of electronics and integrated circuit technology to bridge the gap between research needs and advanced technological solutions. EICT 2024 focused on research areas such as Electronic Science and Technology, Integrated Circuit Design and Integrated System, Electronic and Optical Information Technology, Integration of New Sensing Technologies and Applications, Semiconductor Sensing Electronics, etc., with high academic value. The Conference provided an opportunity for researchers in the fields and related personnel to present their recent theoretical developments as well as practical applications, discuss unsolved problems, and find solutions to them, fostering research and development in electronics and integrated circuit technology. The Conference attracted experts, scholars, researchers, enterprise representatives and relevant personnel from all over the world, showing wide international influence. They shared the latest research results, exchanged technical experiences and explored cooperation opportunities at the Conference, jointly promoting the development of electronics and integrated circuit technology. We would like to highlight the main developments presented at the Conference and introduce the prominent speakers. The invited speakers of the Conference, who performed dramatic speeches on specific subjects combining their own research experience and professional knowledge, are Prof. Wenjie Feng (South China University of Technology, China), Prof. Qiongfeng Shi (Southeast University, China), Prof. Wu Gao (Northwestern Polytechnical University, China), Prof. Chonghua Fang (Dohitech, China), etc. In the study Calculation and Analysis of Quantum Radar Scattering by Prof. Chonghua Fang, a novel method that can deal with the calculation of the orthogonal projected area (A ⊥ ) of the target in each incidence is proposed. In this report, he introduced a three-step computation process of (A ⊥ ), verified the method for typical 2-D targets, and showed some results for typical 3-D convex targets and compared the QRCS with classical radar cross section (CRCS). Meanwhile, he analyzed the superposition of quantum effect of side lobes which means a kind of novel quantum phenomena. In the final foreword, we would like to thank the speakers, authors, reviewers, and all people involved. We also appreciate the members of Technical Program Committee for giving such an opportunity for all of us to share scientific ideas and new developments at the Conference. Last but not the least, our special acknowledgement also goes to the editors of Journal of Physics: Conference Series, for their preparation and assistance in publishing this paper volume. The Committee of EICT 2024 List of Committee Member is available in this Pdf.

Advancements in Quantum Radar Technology An Overview of Experimental Methods and Quantum Electrodynamics Considerations

A closed-form model of bistatic multiphoton quantum radar cross section (QRCS) for the cylindrical surface, the main structure of typical aircraft, especially missiles, is established to analyze the system and scattering characteristics. The influence of curvature of the three-dimensional target on QRCS is analyzed. By comparing and analyzing the bistatic multiphoton QRCS for a cylinder and a rectangular plate, we find that the QRCS for the convex surface target is the extension of the QRCS for the planar target with inhomogeneous atomic arrangement intervals and patterns. The characteristics of cylindrical QRCS are discussed by combining the transceiver system and the photon number of the transmitted signal, and the influences of the cylindrical radius, cylindrical length, and incident photon number on QRCS are analyzed. The bistatic results provide guidance on potential strong scattering directions for the target under various directions of photon incidence. Compared with the plane target, the cylindrical target amplifies scattering intensity near the target surface at the scattering angle side in the bistatic system. A bistatic multiphoton quantum radar system can achieve sharpening and amplification of the main lobe of the QRCS for a cylinder in an extensive scattering angle range. Bistatic multiphoton quantum radar has better visibility for the cylinder with a smaller length. These characteristics will provide prior information for research in many fields, such as photonic technology, radar technology, and precision metrology.

In this study, we explore an approach aimed at enhancing the transmission or reflection coefficients of absorbing materials through the utilization of joint measurements of entangled photon states. On the one hand, through the implementation of photon catalysis in the reflected channel, we can effectively modify the state of the transmission channel, leading to a notable improvement in the transmission ratio. Similarly, this approach holds potential for significantly amplifying the reflection ratio of absorbing materials, which is useful for detecting cooperative targets. On the other hand, employing statistical counting methods based on the technique of heralding on zero photons, we evaluate the influence of our reflection enhancement protocol for detecting noncooperative targets, which is validated through Monte Carlo simulations of a quantum radar setup affected by Gaussian white noise. Our results demonstrate a remarkable enhancement in the signal-to-noise ratio of imaging, albeit with an increase in mean-square error. These findings highlight the potential practical applications of our approach in the implementation of quantum radar.

This paper provides a comprehensive exploration of radar technologies, categorizing them by their unique technological attributes. It delves into phased array radar, known for its rapid directional control, interference resistance, multitasking capabilities, and adaptability. Then compares traditional phased array radar to digital phased array radar and discuss the future potential of phased array radar. Synthetic aperture radar is examined for its all-weather, all-day observation abilities in civilian and military applications, considering performance indicators like frequency, resolution, and repetition observation cycle. Lastly, quantum radar, utilizing quantum entanglement and superposition principles, is discussed for its potential in target detection, ranging, and enhanced system security. Although quantum radar technology is currently not mature and there are still many technical and application challenges, its unique advantages make it a technology with promising prospects. This evolving technology remains indispensable across numerous domains, from defense to agriculture.