Quantum illumination (QI) is a technique exploiting the quantum entanglement between the transmitted signal and the idler to enhance the detection performance of a quantum radar over the classical radar. Here, we propose the double optical parameter amplifier (OPA) detector for QI so that the effect of entanglement between the idler and the returned signal beams is maximized. We show here how even when a weak returned signal is embedded in a large background noise, the probability of detection can be significantly increased.
Quantum illumination (QI) is a technique exploiting the quantum entanglement between the transmitted signal and the idler to enhance the detection performance of a quantum radar over the classical radar. Here, we propose the double optical parameter amplifier (OPA) detector for QI so that the effect of entanglement between the idler and the returned signal beams is maximized. We show here how even when a weak returned signal is embedded in a large background noise, the probability of detection can be significantly increased.
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.
Quantum illumination is a quantum-optical sensing technique in which an entangled source is exploited to improve the detection of a low-reflectivity object that is immersed in a bright thermal background. Here, we describe and analyze a system for applying this technique at microwave frequencies, a more appropriate spectral region for target detection than the optical, due to the naturally occurring bright thermal background in the microwave regime. We use an electro-optomechanical converter to entangle microwave signal and optical idler fields, with the former being sent to probe the target region and the latter being retained at the source. The microwave radiation collected from the target region is then phase conjugated and upconverted into an optical field that is combined with the retained idler in a joint-detection quantum measurement. The error probability of this microwave quantum-illumination system, or quantum radar, is shown to be superior to that of any classical microwave radar of equal transmitted energy.
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.
Based on Quantum illumination (QI) protocol, researcshers have developed prototypes of quantum radar and demonstrated its quantum enhancement. Nevertheless, there are still difficulties in the practical application for QI radar, especially the trade-off between the detection range and quantum enhancement, as well as the construction of the optimized receiver. Some studies have suggested that the potential solutions to these difficulties are to deploy the quantum limited amplifiers in QI radars, and have envisioned different amplification schemes. In this paper, we establish a universal and effective method to evaluate the signal-to-noise ratio of QI radar. It connects QI radar theory with classical radar signal processing theory, providing support for researchers to evaluate the performance of various QI radar schemes from a radar perspective. Based on this method, we prove that any quantum limited phase-insensitive amplification scheme will seriously weaken the quantum enhancement of QI radar. Furthermore, we also demonstrate that the QI radar with phase-sensitive amplified idler has no advantage over the optimal classical illumination. These results can help us avoid some unreasonable QI radar schemes. In addition, we believe that the proposed method can also be applied to explore other potential QI radar schemes and contribute to promoting the application development of QI radar.
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 illumination (QI) is an entanglement-enhanced sensing system whose performance advantage over a comparable classical system survives its usage in an entanglement-breaking scenario plagued by loss and noise. In particular, QI's error-probability exponent for discriminating between equally likely hypotheses of target absence or presence is 6 dB higher than that of the optimum classical system using the same transmitted power. This performance advantage, however, presumes that the target return, when present, has known amplitude and phase, a situation that seldom occurs in light detection and ranging (lidar) applications. At lidar wavelengths, most target surfaces are sufficiently rough that their returns are speckled, i.e., they have Rayleigh-distributed amplitudes and uniformly distributed phases. QI's optical parametric amplifier receiver---which affords a 3 dB better-than-classical error-probability exponent for a return with known amplitude and phase---fails to offer any performance gain for Rayleigh-fading targets. We show that the sum-frequency generation receiver [Zhuang et al., Phys. Rev. Lett. 118, 040801 (2017)]---whose error-probability exponent for a nonfading target achieves QI's full 6 dB advantage over optimum classical operation---outperforms the classical system for Rayleigh-fading targets. In this case, QI's advantage is subexponential: its error probability is lower than the classical system's by a factor of $1/ln(M\overline{\ensuremath{\kappa}}{N}_{S}/{N}_{B})$, when $M\overline{\ensuremath{\kappa}}{N}_{S}/{N}_{B}\ensuremath{\gg}1$, with $M\ensuremath{\gg}1$ being the QI transmitter's time-bandwidth product, ${N}_{S}\ensuremath{\ll}1$ its brightness, $\overline{\ensuremath{\kappa}}$ the target return's average intensity, and NB the background light's brightness.