The quantum radar is a possible technology that can change the situation in the future battlefield. Quantum radars can potentially provide larger RCS (radar cross section), can detect stealth planes, and it is almost impossible to jam them. Therefore, the most advanced countries are working on the development in the head with USA and China.

This article brings an overview of the news about quantum radar in magazines and popular articles as well as in scientific papers for the year 2016.

## Popular Articles

The most of popular articles that mentioned a quantum radar were about the China's announcement of successful development of quantum radar system [globaltimes.cn], [scmp.com] from September. According to these news, China successfully developed a quantum radar able to detect stealth planes 100km away. This quantum radar is developed by Intelligent Perception Technology Laboratory of the 14th Institute China Electronics Technology Group Corporation (CETC) and is based on *single photon detection* (i.e. they do not use entangled photons).

Information about China's quantum radar has been taken over by other media, e.g. [popsci.com], [seekingalpha.com]. Much experts and scientist doubt about this strong announcement about the developing of quantum radar, see e.g. [extremetech.com] or [defensereview.com].

Some popular articles, when they are describing the principle of quantum radar, claim something as the following. If we use two entangled photons, where one photon is held in the radar system and the other is sent to the target, we can see the photon in the radar system only. In addition, if the other photon interacts with some target, he changes also the state of the held photon and this change we can measure.

This is not right, for the technology of quantum radar based on the interferometry as well as quantum illumination both entangled photons need to be measured, i.e. the radiated entangled photon need to be reflected back to the quantum radar. If one of the entangled photons is measured then all "connections" between both photons are destroyed. Therefore, if we would measure the held photon before the interaction of the other photon with a target, we lost connection and we know nothing about the interaction of the other photon. If we would perform the measurement after the interaction of the other photon, we still know nothing, because we do not know the state of the held photon before the interaction and, therefore, we do not know if some interaction occurred. In case of the entanglement quantum radar, the correlations embedded in the entangled states are exploited to increase detection performance.

Next article from December from China [scmp.com] informs about an advance in the weak metrology (weak measurement that does not cause a collapse of quantum states) presented by University of Science and Technology of China (USTC) with strong announcement: *said the technology could “definitely” be used in quantum radar*. In the same article, scientists from Tsinghua University doubt it: *whether the technology would find a practical use any time soon, if at all*.

## Scientific Papers

Matthew J. Brandsema, Ram M. Narayanan, Marco Lanzagorta, *Theoretical and computational analysis of the quantum radar cross section for simple geometrical targets*, Quantum Inf Process (2017) 16:32, [DOI: 10.1007/s11128-016-1494-6] - Authors developed theoretical framework for calculating the QRCS in terms of Fourier transforms. This new framework allows express QRCS for some simple geometries in analytical form and provides an explanation for the aforementioned sidelobe advantage.

Quntao Zhuang, Zheshen Zhang, Jeffrey H. Shapiro, *Optimum mixed-state discrimination for noisy entanglement-enhanced sensing*, Phys. Rev. Lett. 118, 040801, [DOI:10.1103/PhysRevLett.118.040801] - This paper presents an optimum QI-receiver architecture based on sum-frequency generation (SFG), where, in the weak-signal limit, the SFG unitary maps QI target detection to the well-studied problem of single-mode coherent state discrimination. Next, authors suggests feed-forward (FF) mechanism - FF-SFG receiver, whose error probability achieves the Helstrom bound The new receiver architecture presented in this paper can lead realization of multi-mode Gaussian mixed states.

Yi-Tao Wang at al., *Experimental Demonstration of Higher Precision Weak-Value-Based Metrology Using Power Recycling*, Phys. Rev. Lett. 117, 230801, [DOI: 10.1103/PhysRevLett.117.230801] - Paper describes that the weak-value-based metrology signal can be strengthened by power recycling and authors demonstrate this method experimentally. This paper is commented in [scmp.com].

U. Las Heras, R. Di Candia, K. G. Fedorov, F. Deppe, M. Sanz, E. Solano; *Quantum Illumination Unveils Cloaking*; arXiv:1611.10280 [quant-ph] - Authors present a quantum illumination protocol allowing for a 3 dB improvement in the detection of a cloaked target (a stealth technology).

## Conferences

Radar Sensor Technology XX, Baltimore, Maryland, United States, April 17, 2016 with the following relevant contributions:

*The generalized ambiguity function: a bridgework between classical and quantum radar*,

John E. Gray, Allen D. Parks, doi: 10.1117/12.2223184*Improving quantum sensing efficiency with virtual modes*, Marco Lanzagorta, Jeffrey Uhlmann, Truc Le, Oliverio Jitrik, Salvador E. Venegas-Andraca, doi: 10.1117/12.2223981*Clutter attenuation using the Doppler effect in standoff electromagnetic quantum sensing*, Marco Lanzagorta, Oliverio Jitrik, Jeffrey Uhlmann, Salvador Venegas, doi: 10.1117/12.2223972*A quantum radar detection protocol for fringe visibility enhancement*, Benjamin Koltenbah, Claudio Parazzoli, Barbara Capron, doi: 10.1117/12.2228258*Quantum seismography*, Marco Lanzagorta, Oliverio Jitrik, Jeffrey Uhlmann, Salvador Venegas, doi: 10.1117/12.2223831*Analytical formulation of the quantum electromagnetic cross section*, Matthew J. Brandsema, Ram M. Narayanan, Marco Lanzagorta, doi: 10.1117/12.2224026*Quantum computation of the electromagnetic cross section of dielectric targets*, Marco Lanzagorta, Jeffrey Uhlmann, Oliverio Jitrik, Salvador E. Venegas-Andraca, Seth Wiesman, doi: 10.1117/12.2224078

**Some other proceedings:**

Genta Masada,* Two-mode squeezed light source for quantum illumination and quantum imaging II*, Proc. SPIE 9980, Quantum Communications and Quantum Imaging XIV, 99800T, [DOI: 10.1117/12.2237546] - In this proceeding, the author is developing a high-quality two-mode squeezed light source for exploring the possibility of a quantum radar system based on a quantum illumination method.

Konstantin Lukin; *Quantum Radar vs Noise Radar*, 2016 9th International Kharkiv Symposium on Physics and Engineering of Microwaves; Millimeter and Submillimeter Waves (MSMW), Kharkiv, 2016, [DOI: 10.1109/MSMW.2016.7538137].

Ankur Saharia, Sonali Bansal, A Review on Quantum Radar Technology and its Application in Defence Equipment, SSRG IJECE Volume 3 Issue 8 - Authors only summarize the known facts about quantum radar. Nothing new, no own original work.

K. Liu, Y. Jiang, X. Li, Y. Cheng and Y. Qin; *New results about quantum scattering characteristics of typical targets;* *2016 IEEE International Geoscience and Remote Sensing Symposium (IGARSS)*, Beijing, 2016, [DOI: 10.1109/IGARSS.2016.7729689].

## Summary

Popular articles about quantum radars were only about the China quantum radar program that undoubtedly is in development but the real progress most probably does not correspond to the results and abilities presented in the media.

The results for the year 2016 shows that scientists and researchers focus primary on the development of quantum sensing systems, mainly quantum illumination method, probably the most promising concept for quantum radar. Next, researchers also focus on the description of the quantum radar cross section (QRCS) where the more complicated shapes are still a challenge.

Of course, this overview is only about public papers and articles. Certainly, at least USA and China are working on the development of quantum radar in secret, and it is not easy to estimate their real progress. However, most probably there is not a working prototype of quantum radar in the microwave regime.