The Internet is agog with stories about quantum radar. Will it really make stealth aircraft vulnerable? Were the microwave experiments reported in 2020 from Europe and Canada really proof-of-principle laboratory demonstrations of quantum radar's advantage over classical radar? Or, does the 25 September 2020 news article in Science-entitled "The short, strange life of quantum radar"-paint the true picture? This paper disentangles microwave quantum radar's alphabet soup: quantum illumination (QI) radar, quantum illumination with a microwave parametric amplifier receiver (QI-MPA) radar, quantum-correlated noise (QCN) radar, and quantum-correlated noise radar with a correlation receiver (QCN-CR). In particular, it evaluates-with no explicit quantum-mechanical notation or calculations-these radars' miss probabilities at fixed false-alarm probability and it compares them to those for classical radar's relevant alphabet soup, viz., coherent-state homodyne (CS-Hom) radar, coherent-state heterodyne (CS-Het) radar, classically-correlated noise (CCN) radar, and classically-correlated noise radar with a correlation receiver (CCN-CR). These comparisons show that, under ideal operating conditions, the QI and QI-MPA radars offer performance advantages over their best classical counterparts. Moreover, QI-MPA's advantage is similar to that for its error-probability exponent when target absence and presence are equally likely and all radars make minimum error-probability decisions based on their respective measurements. Available theory, however, is unable to fully quantify QI's advantage in the operating regime of interest. Ultimately-after accounting for problems that afflict QI and QI-MPA, but not their classical competitors, and factoring in realistic standoff-sensing parameters-it will be concluded that the aforementioned Science article has it correct. QI target detection has little to offer for standoff sensing, i.e., it does not compromise stealth aircraft.
The Internet is agog with stories about quantum radar. Will it really make stealth aircraft vulnerable? Were the microwave experiments reported in 2020 from Europe and Canada really proof-of-principle laboratory demonstrations of quantum radar's advantage over classical radar? Or, does the 25 September 2020 news article in Science-entitled "The short, strange life of quantum radar"-paint the true picture? This paper disentangles microwave quantum radar's alphabet soup: quantum illumination (QI) radar, quantum illumination with a microwave parametric amplifier receiver (QI-MPA) radar, quantum-correlated noise (QCN) radar, and quantum-correlated noise radar with a correlation receiver (QCN-CR). In particular, it evaluates-with no explicit quantum-mechanical notation or calculations-these radars' miss probabilities at fixed false-alarm probability and it compares them to those for classical radar's relevant alphabet soup, viz., coherent-state homodyne (CS-Hom) radar, coherent-state heterodyne (CS-Het) radar, classically-correlated noise (CCN) radar, and classically-correlated noise radar with a correlation receiver (CCN-CR). These comparisons show that, under ideal operating conditions, the QI and QI-MPA radars offer performance advantages over their best classical counterparts. Moreover, QI-MPA's advantage is similar to that for its error-probability exponent when target absence and presence are equally likely and all radars make minimum error-probability decisions based on their respective measurements. Available theory, however, is unable to fully quantify QI's advantage in the operating regime of interest. Ultimately-after accounting for problems that afflict QI and QI-MPA, but not their classical competitors, and factoring in realistic standoff-sensing parameters-it will be concluded that the aforementioned Science article has it correct. QI target detection has little to offer for standoff sensing, i.e., it does not compromise stealth aircraft.
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.
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.
We propose a hetero-homodyne receiver for quantum illumination (QI) target detection. Unlike prior QI receivers, it uses a cascaded positive operator-valued measurement (POVM) that does not require a quantum interaction between QI's returned radiation and its stored idler. When used without sequential detection its performance matches the 3-dB quantum advantage over optimum classical illumination (CI) that Guha and Erkmen's [Phys. Rev. A 80, 052310 (2009)] phase-conjugate and parametric amplifier receivers enjoy. When used in a sequential detection QI protocol, the hetero-homodyne receiver offers a 9-dB quantum advantage over a conventional CI radar, and a 3-dB advantage over a CI radar with sequential detection. Our work is a significant step forward toward a practical quantum radar for the microwave region, and, more generally, emphasizes the potential offered by cascaded POVMs for quantum radar.
A Doppler radar is a device that employs the Doppler effect to estimate the radial velocity of a moving target at a distance. Traditional radars are based on a classical description of the electromagnetic radiation, but in principle their performance can be improved employing entangled quantum probe states. For target detection, i.e. hypothesis testing, a quantum advantage exists even in the high-noise regime appropriate to describe microwave fields, a protocol known as quantum illumination. In this paper, we show a similar advantage also for a quantum Doppler radar operating in presence of thermal noise, whereas so far a quantum advantage was shown in the noiseless scenario or in lidars operating at optical frequencies with negligible thermal noise. Concretely, we quantify the radar performance in terms of the quantum Fisher information, which captures the ultimate precision allowed by quantum mechanics in the asymptotic regime. We compare a classical protocol based on coherent states with a quantum one that uses multimode states obtained from spontaneous parametric downconversion. To ensure a fair comparison we match the signal energy and pulse duration. We show that a 3dB advantage is possible in the regime of small number of signal photons and high thermal noise, even for low transmissivity.
Abstract Based on quantum illumination (QI) protocol, microwave quantum radar has been developed, which has attracted great interest from radar researchers. While, according to the QI protocol, the quantum advantage of QI radar is related to the power of generated signal, which may lead to a trade‐off between its quantum advantage and the maximum detection range. However, the maximum detection range is an important indicator to measure the performance of the radar. Therefore, it is necessary to quantitatively analyse the maximum detection range and quantum advantages of microwave QI radar, which will help us understand its performance from the perspective of radar applications and further evaluate the potential application scenarios and future research directions of it. The microwave quantum radar equation is developed, by the authors, based on the classical radar equation with the consideration of the quantum properties of extremely weak signals. Then, the maximum detection range of QI radar and classical two mode noise radar in different microwave bands is comprehensively compared and analysed. The possible applications of microwave QI radars in different bands are also discussed. In addition, the authors demonstrate that the symmetrical quantum limited amplification actually has no contribution to improving the detection range of a QI radar.
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.