Quantum Orbital Angular Momentum (OAM) indicates that each Electro-Magnetic (EM) photon of an EM wave carries OAM. In the microwave band, such an EM wave photon is called a vortex microwave photon. Physical properties distinguish between EM waves with vortex and plane wave photons. When illuminating a traditional stealthy target composed of absorbing materials, a vortex microwave photon can achieve higher echo power, thereby improving the Radar Cross Section (RCS), the corresponding receiving signal power, and detection probability. Hence, the vortex microwave photon shows promise in antistealth technology. In this paper, a vortex microwave quantum radar based on the OAM quantum state is proposed. Its basic physical architecture and corresponding mathematical model are given, and the high echo power characteristics of the vortex microwave photon are analyzed using Quantum Electro-Dynamics (QED). The correctness of the theoretical calculation was experimentally verified with an approximate 9 dB improvement in echo power. Moreover, the simulations are performed to clarify the improvement in radar performance, including the receiving power and detection probability, illustrating the capability of the vortex microwave photon when applied to antistealth radar.
Quantum Orbital Angular Momentum (OAM) indicates that each Electro-Magnetic (EM) photon of an EM wave carries OAM. In the microwave band, such an EM wave photon is called a vortex microwave photon. Physical properties distinguish between EM waves with vortex and plane wave photons. When illuminating a traditional stealthy target composed of absorbing materials, a vortex microwave photon can achieve higher echo power, thereby improving the Radar Cross Section (RCS), the corresponding receiving signal power, and detection probability. Hence, the vortex microwave photon shows promise in antistealth technology. In this paper, a vortex microwave quantum radar based on the OAM quantum state is proposed. Its basic physical architecture and corresponding mathematical model are given, and the high echo power characteristics of the vortex microwave photon are analyzed using Quantum Electro-Dynamics (QED). The correctness of the theoretical calculation was experimentally verified with an approximate 9 dB improvement in echo power. Moreover, the simulations are performed to clarify the improvement in radar performance, including the receiving power and detection probability, illustrating the capability of the vortex microwave photon when applied to antistealth radar.
The orbital angular momentum (OAM) technology, promising for future communications, radar, and quantum information processing, confronts challenges in OAM detection of the microwave photons, due to the noise and equipment complexity. Conventional detection approaches based on gyrotron systems, which demand vacuum and high-voltage environments, prove impractical for scalable applications. Thus, we introduce a Rydberg-atom-based architecture for OAM detection of vortex microwave photons, which operates in normal pressure and low voltage with miniaturized equipment. Specifically, leveraging the unique dipole-forbidden, quadrupole-allowed transitions of Rydberg atoms, we can receive the vortex microwave photons and identify the corresponding intrinsic OAM (IOAM), with precise frequency alignment by external electrode plates for fine-tuning. Moreover, experimental observations reveal the insight of Autler–Townes splitting, confirming that the OAM of microwave photons can couple to atomic energy levels through electric-quadrupole interactions, inducing a dynamic Stark effect. In contrast, the experiments with plane microwave photons, i.e., the OAM mode is zero, show the result with only static stark broadening rather than the peak splitting, which highlights the critical role of quadrupole transitions in OAM detection. Significantly, this approach overcomes the limitations of conventional techniques requiring high-energy superconducting devices or high-voltage setups, offering a low-cost, scalable solution for efficient vortex microwave photons detection with promising applications, e.g., secure wireless communications and quantum radars.
Quantum radar has emerged as a promising sensing paradigm that exploits quantum resources, including entanglement and quantum correlations, to enhance target detection in noisy and lossy environments. Although entanglement generated by superconducting devices such as Josephson parametric amplifiers, Josephson parametric converters, and Josephson traveling-wave parametric amplifiers is rapidly degraded under realistic propagation conditions, the remaining quantum correlations can still provide a measurable detection advantage through the principles of quantum illumination. This review presents a comprehensive engineering perspective on quantum radar, covering the theoretical foundations of quantum illumination, microwave entanglement generation, electro-optomechanical quantum transducers, atmospheric channel effects, cryogenic receiver architectures, and digital signal-processing techniques. Recent microwave experimental demonstrations are also reviewed, highlighting the transition from theoretical concepts to laboratory-scale implementations. Collectively, these developments demonstrate that microwave quantum radar is evolving toward practical sensing architectures while emphasizing the engineering challenges that must be addressed before real-world deployment.
Detection of low-reflectivity objects can be improved by the so-called Quantum Illumination (QI) procedure. However, quantum detection error probability exponentially decays with the source bandwidth. The Josephson Parametric Amplifiers (JPAs) technology utilized as a source, generating pairs of entangled signals called two-mode squeezed vacuum states, shows a very narrow bandwidth limiting the operation of the Microwave Quantum Illumination (MQI) systems. In this paper, for the first time, a microwave quantum radar setup based on quantum illumination protocol and using a Josephson Traveling Wave Parametric Amplifier (JTWPA) is proposed. We experimentally demonstrate the generation and control of three-wave mixing modes produced by a JTWPA, key enabler radiation source for MQI schemes. Measurement results of the developed JTWPA, pumped at 12 GHz, show the capability to generate entangled modes in the X-band, making our MQI system a promising candidate for the detection of stealth objects.
Quantum illumination (QI) is a quantum sensing protocol mainly for target detection which uses entangled signal-idler photon pairs to enhance the detection efficiency of low-reflectivity objects that are immersed in thermal noisy environments. Due to the naturally occurring background radiation, the photon emitted toward potential targets more appropriately lies in the microwave region. Here, we propose a hybrid quantum source based on cavity magnonics for microwave QI, where the medium that bridges the optical and the microwave modes is magnon, the quanta of spin wave. Within experimentally accessible parameters, significant microwave-optical quantum resources of interest can be generated, leading to orders of magnitude lower detecting error probability compared with the electro-optomechanical prototype quantum radar and any classical microwave radar with equal transmitted energy.
Quantum radar is an emerging technique, currently at the experimental stage, that promises to disrupt the well-established field of conventional radar. Recent progress shows that it is possible to generate and use entangled pairs of microwave photons for detection purposes and to obtain an advantage over a classical radar. In this work, we study the currently experimentally feasible type of quantum correlation radar. To this end, we compare different radar architectures, quantum and classical, by analyzing their detection performances by means of the receiver operating characteristic (ROC), the minimum error probability as well as the Chernoff bound. The underlying system models are based on quantum mechanical formulations as well as conventional signal theory. Where it is appropriate and necessary to facilitate our analysis, we apply the central limit theorem to establish the Gaussianity of the observable quantities. A conceptual analogy between the quantum and classic points-of-view is drawn and supported by results showing the asymptotic behavior of the ROC curves of both physical descriptions depending on the power levels of signal and noise. We come to exact and comprehensible conclusions on the current state of quantum radar in comparison to classic radar with a detailed mapping of the radar operating regime (measurement time, signal-to-noise ratio, environmental noise level, target object size and distance) in which a quantum advantage is attainable.
Quantum radar represents a promising advancement over classical radar systems by exploiting quantum mechanical phenomena such as entanglement and quantum measurement to overcome fundamental detection limitations. This paper reviews the evolution of radar technology from conventional radar frequency systems to quantum radar architectures, with emphasis on sensitivity enhancement and detection of RF-stealth targets for military defense applications. Classical radar parameters such as radar range, transmitted power and cross section are revisited and extended to their quantum analogues. The role of entangled single photon sources in improving detection performance under high noise and jamming environments is discussed. Context of microwave quantum radar is reviewed along with photonic implementations. This paper further highlights the importance of quantum measurement theory, including system-apparatus entanglement, density matrix formalism and wave function collapse in extracting information from quantum radar systems. Although significant experimental challenges remain, recent advances indicate strong potential for future development of quantum radar in next generation defense and surveillance systems.