In conventional microwave quantum detection systems, single-photon detection suffers from low signal-to-noise ratio (SNR), requiring extremely high receiver sensitivity that should make the detection system work in low-temperature environment. Although multi-photon accumulation can improve system performance, conventional multi-photon accumulation techniques provide limited SNR enhancement. To address this challenge, a quantum correlation detection based on compact array configuration is proposed. Two identical receiving units combined with correlation processing is exploited to enhance SNR effectively. Firstly, a target detection model using the compact array is established. Subsequently, the signal processing procedure for correlation detection is mathematically derived, with detailed analysis of the relationship between accumulated photon number and SNR. Finally, the effectiveness of the methodology is validated through comprehensive simulations, demonstrating superior performance compared to conventional techniques.
In conventional microwave quantum detection systems, single-photon detection suffers from low signal-to-noise ratio (SNR), requiring extremely high receiver sensitivity that should make the detection system work in low-temperature environment. Although multi-photon accumulation can improve system performance, conventional multi-photon accumulation techniques provide limited SNR enhancement. To address this challenge, a quantum correlation detection based on compact array configuration is proposed. Two identical receiving units combined with correlation processing is exploited to enhance SNR effectively. Firstly, a target detection model using the compact array is established. Subsequently, the signal processing procedure for correlation detection is mathematically derived, with detailed analysis of the relationship between accumulated photon number and SNR. Finally, the effectiveness of the methodology is validated through comprehensive simulations, demonstrating superior performance compared to conventional techniques.
In lossy and noisy environments, quantum-enhanced target detection based on temporal quantum correlation encounters low signal-to-noise ratio (SNR), resulting in poor detection performance. To address these challenges, we propose a multi-channel temporal correlation scheme. In this scheme, signal photons from multiple independent entangled sources illuminate the target and arrive at the same detector. Coincidences are obtained by correlation measurements of the entangled photons on one signal path and different reference paths. We then propose a weighted average processing method for fusing the coincidences to obtain higher SNR. The relationship between the SNR and the number of sources is analyzed for different background noise levels. It is shown that the SNR increases as the number of sources increases, but eventually approaches a limit. Experimental results verify the correction of our theoretical analysis.
This article presents a comprehensive analysis of two classes of quantum radars, including quantum direct-detection and quantum-entangled noise radars. In the first case, inspired by the well-established concept of single-photon LiDARs, we investigated the performance of single-photon radars, in which state-of-the-art single microwave-photon detectors are employed to enhance the detection sensitivity and enable the detection of weaker signals. We derived analytical expressions for the maximum detection range of both classes of quantum radars in terms of the Lambert W function, by considering all relevant system, target, and environmental parameters. Our formulation facilitates direct comparison of noise radars with direct-detection radars and suggests that a quantum-entangled noise radar can be regarded as an enhanced direct-detection radar with an effective threshold signal-to-noise ratio. Furthermore, we applied this framework to classical-correlated noise radars and defined the parameter range enhancement factor (REF) to quantify the superiority of quantum-entangled noise radars over their classical counterparts. Moreover, we introduced a rule-of-thumb for approximating the REF. We also examined the influence of limitations imposed by various microwave detection technologies. Our analysis shows that the conventional antennas limit the potential benefits of quantum-entangled noise radar systems. We also demonstrated that the optimal detection method for these radars is a microwave detector based on a quantum transducer combined with a single optical-photon detector. We showed that, with the current technology, implementing a quantum-entangled noise radar with the maximum detection range on the order of few kilometers is possible. Finally, we explored the potential applications of quantum-entangled noise radars.
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.
Microwave quantum illumination (QI) represents a paradigm shift in low-power wireless radar detection, leveraging entanglement between signal and idler microwave photons to achieve detection performance exceeding classical limits by up to 6 dB in error exponent, particularly in high-noise environments where traditional coherent radars falter. This comprehensive survey delineates the theoretical foundations and practical protocols of microwave QI, beginning with two-mode squeezed vacuum state generation using Josephson parametric amplifiers in cryogenic setups, which produce highly correlated photon pairs resilient to channel decoherence. Receiver architectures, including optical parametric amplifier-single-photon avalanche diode (OPA-SPADE) systems with sum-frequency generation for joint measurements and digital phase-conjugation for computational correlation recovery, enable efficient extraction of quantum discord even after significant atmospheric loss or low target reflectivity (under 1%).Performance analyses under realistic thermal noise models ( ) and -loss channels confirm sustained quantum advantages via the quantum Chernoff exponent , validated by ray-tracing simulations showing doubled detection range at fixed power and lab experiments at 10 GHz carriers detecting weak reflectors amid 100 K noise. Low-power optimizations such as adaptive entanglement tuning, chirped pulse shaping, and neural network-aided parameter selection yield 50% energy reductions without sacrificing fidelity, making QI viable for battery-limited platforms. Applications encompass short-range automotive/UAV radar for fog-penetrating obstacle avoidance, non-invasive biomedical subsurface imaging with safe radiation levels, covert perimeter security against jamming, and seamless integration into 6G networks via joint communication-sensing waveforms at mm Wave/THz bands. The paper identifies key challenges including multi-target scalability, real-time gigascale processing, and quantum RF interface standardization, proposing hybrid quantum-classical frameworks and entanglement-swapped sensor arrays as pathways to deployment. This work bridges quantum optics with RF engineering, equipping researchers with blueprints for prototyping transformative quantum-enhanced wireless sensing systems.
We investigate the use of correlated photon pair sources for the improved quantum-level detection of a target in the presence of a noise background. Photon pairs are generated by spontaneous four-wave mixing, one photon from each pair (the herald) is measured locally while the other (the signal) is sent to illuminate the target. Following diffuse reflection from the target, the signal photons are detected by a receiver and nonclassical timing correlations between the signal and herald are measured in the presence of a configurable background noise source. Quantum correlations from the photon pair source can be used to provide an enhanced signal-to-noise ratio when compared to a classical light source of the same intensity.
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.