Quantum radar, China successfully developed

Last month, China's first quantum based on single photon detection radar system developed in 14, reached the international advanced level. The quantum radar system by China electric section 14 by intelligent perception technology focus laboratory development, in China Science and Technology University, and China electric section 27 by and Nanjing University, collaboration units of common efforts Xia, after tireless of efforts, completed has quantum detection mechanism, and target scattering characteristics research and quantum detection principle of experiment validation, and in outfield completed real atmosphere environment Xia target detection test, get hundred km level detection power, detection sensitivity great improve, index are reached expected effect, Achieved significant progress and achievement.

Domestic research team have been in quantum communication and quantum computation after obtaining the technological breakthroughs, and China in the field of quantum radar is another city. So classic and quantum radar radar, what is so special about it?

Quantum radar team outfield picture

　　Quantum radar is not a classic reversal radar

Radar the first large scale application in World War II, especially in the battle of Britain in the United Kingdom Royal Air Force rely on radar-assisted Germany air force caused great destruction. The radar simply transmit electromagnetic signals through surface scattering, by judging the received signal power, to identify and target. However, this radar information carriers only through the absolute signal amplitude or changes to reflect, the detection mechanism is the simple energy detection, unable to distinguish between clutter and target, confusing flying in the air foil with real fighters, single information uses, therefore, applications are subject to greater restrictions.

With the development of technology, radar is also changing, from simple signal strength information, evolving into integrated frequency and phase information using electromagnetic signals, that is, second-order characteristics of electromagnetic. Through the application of electromagnetic characteristics of second order, on the modulation, emergence of a linear frequency modulation, phase-coded and complex frequency-agile signals, such forms of signals effectively solves the traditional radar bandwidth and bandwidth is a contradiction, and enhance the ability of radar anti-jamming, and clutter. On the detection technology, gave birth to the moving target detection technology, space-time Adaptive processing technique and pulsed Doppler system, these targets and clutter in Doppler domain differences to achieve effective detection of moving objects in clutter, improve the ability of radar clutter.

Quantum radar is the quantum information technology into classic area of radar detection, solve classic radar in the detection, measurement and imaging technologies such as bottlenecks, improve radar performance. Quantum radar belongs to a new concept radar, primary application is achieved target has no of detection, this based Shang can further extended application field, including quantum imaging radar, and quantum ranging radar and quantum navigation radar,, from essentially for, quantum radar and no from classic radar detection of framework system, just in using quantum theory for system analysis Shi, on radar in the some concept and physical phenomenon, as receiver noise,, has new of, and more accurate of understanding. On this basis, quantum carrier modulation and detection of radar information processing in a bid to enhance radar performance. In General, quantum radar is an update and supplement to the classic theory of radar instead of subversion and replaced.

　　Quantum radar classifications

According to the different quantum phenomena and mechanisms of photon emission, quantum radar can be divided into the following 3 categories:

Quantum radar is non-entangled quantum state of electromagnetic waves. Single photon pulse transmitter probe target area that may exist, if the target exists, then the signal photons will be with a certain probability of returning to the receiver, by measuring return photons can extract the target information.

Quantum radar is launching the second entangled quantum state of electromagnetic waves. Its detection process for using pump Pu photon through (BBO) Crystal, through parameter Xia conversion produced large entanglement photon on, the entanglement photon on Zhijian of polarization state each other orthogonal, will entanglement of photon on is divided into detection photon and imaging Photon, imaging photon retained in quantum memory in the, detection photon by transmitter launches by target reflection Hou, was quantum radar received, according to detection photon and imaging photon of entanglement associated can improve radar of detection performance. Compared with not using entangled quantum radar, using entangled quantum radar resolution based on quadratic rate increase.

Three is a classic State radar electromagnetic wave. At the receiver using quantum-enhanced detection techniques to enhance the performance of the radar system, at present, the technologies in laser radar technology has a wide range of applications. 14 in fact is one of the above three modes of the application.

Quantum radar technology

At present, the classic radar has some shortcomings, one is the power (tens of Watts), electromagnetic leakage; the second is the stealth ability is relatively poor; the third is Imaging ability is relatively weak; four is a complex signal processing, real-time performance weak. Classic of radar technology, quantum information technology, there are technical advantages can be combined with classical radar to improve radar detection performance.

First, the quantum information carriers into a single quantum of information technology, signal generation, modulation, and receiving, testing object is a single quantum of, so that the receiving system has a very high sensitivity, namely quantum receives very low noise floor systems than classical radar receiver noise basement can reduce several orders of magnitude. Additional implementation factors such as frequency, noise and dynamic range, the radar range can be increased by several times and even dozens of times. Which greatly enhanced radar weak target, even the detection of stealthy targets.

Second, modulation of quantum state in quantum information technology, compared to classic modulated radar information, quantum States can be used to characterize quantum "fluctuation", such as information, than the classic, frequency, polarization, and other more advanced information, namely information dimensions higher. From the viewpoint of information theory, through the operation of high-dimensional information, you can get more performance. For target detection,, through higher order information modulation, can in not effect accumulated thanks of premise Xia, further down noise basement, to upgrade noise in the weak target detection of capacity; from signal analysis angle starting, through on signal for quantum higher order micro modulation, makes traditional signal analysis method to accurate extraction levy signal in the modulation of information, to upgrade in electronic against environment Xia of anti-listens capacity. Integrated,, through quantum information technology of introduced, through quantum of received, principle Shang can effective reduced received signal in the of noise basement power; through quantum state modulation, principle Shang can increased information processing of dimension degrees, while can upgrade letter noise than thanks, on the can reduced launches signal was accurate analysis and copy of possibilities, to in target detection and electronic against field has broad of application potential.

　　In the international advanced level

Disclosure according to experts, in fact, related research has been done for many years, quantum imaging, work done before and not in single photon level, but ran out of higher-order correlation of imaging characteristics indeed break through the clouds and other features, but the imaging process is quite complex, process long practicality remains to be developed, and it is difficult to say is called quantum Imaging. It can be said that this technical breakthrough is the result of years of accumulated technology, not in order to catch up with the recent "Mozi" quantum set off heat.

This technology breakthrough quantum detection area, characterised by breakthrough now classical limit of measurement methods (such as the diffraction limit of light), an industry-more promising technologies (admittedly, some scholars have objections). World also has research and technology developing fast-2008 United States Massachusetts Institute of technology Professor Lloyd first quantum-quantum radiation radar remote detection system model, proved that quantum mechanics can be applied to the remote target detection. In 2012, Nakamura and Yamamoto uses superconducting loop, University of Tokyo, has made microwave frequency single-photon State generation and reception of new breakthroughs and squeezed. In 2013, Italy Lopaeva by exposure to experimental methods quantum radar for the first time, the experiment is based on photon number associated validated Lloyd's quantum radiation model of radar detection in high noise and high loss still target detection capability in 2015, Germany Shabir Barzanjeh, Aachen University of technology of microwave plasma lighting detection, for further research.

At present, China only at the advanced level in that area, are not the leading State, revolution has not succeeded yet, comrades should still work hard.

(Thank the industry experts for this guide! Author app public number: tieliu1988)

　　References:

The quantum based on the probability wave detection radar systems principles of Tan Hong, Zhao Mingwang, Korea

The basic principles of quantum radar to detect targets and progress, Jiang Tao, Sun

(Editors: Liu Cheng UN649)
2016-09-07 13:26:17
Observer network

中国量子雷达研制成功

　　上月，中国电科首部基于单光子检测的量子雷达系统在14所研制成功，达到国际先进水平。该量子雷达系统由中国电科14所智能感知技术重点实验室研制，在中国科学技术大学、中国电科27所以及南京大学等协作单位的共同努力下，经过不懈的努力，完成了量子探测机理、目标散射特性研究以及量子探测原理的实验验证，并且在外场完成真实大气环境下目标探测试验，获得百公里级探测威力，探测灵敏度极大提高，指标均达到预期效果，取得阶段性重大研究进展与成果。

　　国内科研团队相继在量子通信和量子计算上取得技术突破后，中国在量子雷达领域再下一城。那么，和经典雷达相比量子雷达又有何特殊之处呢？

量子雷达团队外场合影

　　量子雷达不是对经典雷达的颠覆

　　雷达最早在二战期间得到大规模应用，特别是在不列颠空战中，英国皇家空军依靠雷达的辅助对德国空军造成较大杀伤。当时的雷达单纯利用发射的电磁波信号，经过目标表面散射后，通过判断接收信号的能量，来识别、判断目标。不过，这种雷达的信息载体只能通过信号的绝对幅度或幅度的变化来体现，检测机理就是简单的能量检测，无法区分杂波和目标，分不清在空中飞舞的锡箔条和真正的战机，信息利用方式单一，因此，应用领域受到较大的限制。

　　随着技术的发展，雷达也不断发生变化，从单纯利用信号的强度信息，演化为综合利用电磁信号的频率和相位信息，即电磁场的二阶特性。通过发射电磁波二阶特性的应用，在调制方式上，出现了线性调频、相位编码和捷变频等复杂信号形式，这些信号形式有效解决了传统雷达时宽与带宽的矛盾，并提升雷达抗干扰、抗杂波的能力。在检测技术上，催生了动目标检测技术、空时自适应处理技术和脉冲多普勒体制，这些技术利用目标和杂波在多普勒域上的差异，实现杂波中运动目标的有效检测，提升雷达抗杂波能力。

　　量子雷达则是将量子信息技术引入经典雷达探测领域，解决经典雷达在探测、测量和成像等方面的技术瓶颈，提升雷达的综合性能。量子雷达属于一种新概念雷达，首要应用是实现目标有无的探测，在此基础上可以进一步扩展应用领域，包括量子成像雷达、量子测距雷达和量子导航雷达等，从本质上来说，量子雷达并没有脱离经典雷达探测的框架体系，只是在利用量子理论进行系统分析时，对雷达中一些概念和物理现象，如接收机噪声等，具有全新的、更准确的理解。在此基础上，量子雷达从信息调制载体和检测处理等方面入手，提升雷达的性能。总体而言，量子雷达是对经典雷达理论的更新和补充，而不是颠覆和取代。

　　量子雷达的分类

　　根据利用量子现象和光子发射机制的不同，量子雷达主要可以分为以下3个类别：

　　一是量子雷达发射非纠缠的量子态电磁波。发射机发射单光子脉冲探询目标可能存在的区域，如果目标存在，则信号光子将会以一定的概率返回至接收机处，通过对返回光子状态的测量可以提取出目标信息。

　　二是量子雷达发射纠缠的量子态电磁波。其探测过程为利用泵浦光子穿过（BBO）晶体，通过参量下转换产生大量纠缠光子对，各纠缠光子对之间的偏振态彼此正交，将纠缠的光子对分为探测光子和成像光子，成像光子保留在量子存储器中，探测光子由发射机发射经目标反射后，被量子雷达接收，根据探测光子和成像光子的纠缠关联可提高雷达的探测性能。与不采用纠缠的量子雷达相比，采用纠缠的量子雷达分辨率以二次方速率提高。

　　三是雷达发射经典态的电磁波。在接收机处使用量子增强检测技术以提升雷达系统的性能，目前，该技术在激光雷达技术中有着广泛的应用。中电14所实际上应用的是上述三种模式中的一种。

量子雷达的技术优势

　　目前，经典雷达存在一些缺点，一是发射功率大（几十千瓦），电磁泄漏大；二是反隐身能力相对较差；三是成像能力相对较弱；四是信号处理复杂，实时性弱。针对经典雷达存在的技术难点，量子信息技术均存在一定的技术优势，可以通过与经典雷达相结合，提升雷达的探测性能。

　　首先，量子信息技术中的信息载体为单个量子，信号的产生、调制和接收、检测的对象均为单个量子，因此整个接收系统具有极高的灵敏度，即量子接收系统的噪声基底极低，相比经典雷达的接收机，噪声基底能够降低若干个数量级。再忽略工作频段、杂波和动态范围等实现因素，则雷达作用距离可以大幅提升数倍甚至数十倍。从而大大提升雷达对于微弱目标，甚至隐身目标的探测能力。

　　其次，量子信息技术中的调制对象为量子态，相比较经典雷达的信息调制对象，量子态可以表征量子“涨落变化”等微观信息，具有比经典时、频、极化等更加高阶的信息，即调制信息维度更高。从信息论角度出发，通过对高维信息的操作，可以获取更多的性能。对于目标探测而言，通过高阶信息调制，可以在不影响积累得益的前提下，进一步压低噪声基底，从而提升噪声中微弱目标检测的能力；从信号分析角度出发，通过对信号进行量子高阶微观调制，使得传统信号分析方法难以准确提取征收信号中调制的信息，从而提升在电子对抗环境下的抗侦听能力。综合而言，通过量子信息技术的引入，通过量子化接收，原理上可以有效降低接收信号中的噪声基底功率；通过量子态调制，原理上可以增加信息处理的维度，一方面可以提升信噪比得益，另一方面可以降低发射信号被准确分析和复制的可能性，从而在目标探测和电子对抗领域具有广阔的应用潜力。

　　处于国际先进水平

　　据专家披露，其实相关研究已经做了很多年，之前做的量子成像方面的工作，并没有在单光子水平上，而是用光的高阶关联特性实现的成像，确实有突破云雾等的特点，但成像过程还是比较复杂的，流程也较漫长，实用性还有待发展，而且很难说叫量子成像。可以说，本次实现的技术突破是多年技术积累的结果，并非为了追赶近期“墨子”号掀起的量子热。

　　本次技术突破属于量子探测领域，特点就是突破现在测量方法的经典极限（例如光的衍射极限等），是业界比较看好的技术（诚然，也有学者对此有异议）。世界各国对此也都有研究，而且技术发展较快——2008年美国麻省理工学院的Lloyd教授首次提出了量子远程探测系统模型—量子照射雷达，从理论上证明了量子力学可以应用于远程目标探测。2012年，东京大学的Nakamura和Yamamoto采用超导回路，取得了微波频段单光子态和压缩态产生与接收技术的新突破。2013年，意大利的Lopaeva等首次用实验方法实现了量子照射雷达，该实验基于光子数关联，验证了Lloyd提出的量子照射雷达模型探测在高噪声及高损耗时依然有目标探测能力；2015年，德国亚琛工业大学的Shabir Barzanjeh等对微波量子照明探测进行了深入研究。

　　目前，中国在该领域仅仅处于技术先进水平，还不是领先状态，革命尚未成功，同志们仍需努力。

　　（感谢业内专家对本文的指导！作者微信公众号：tieliu1988）

　　参考文献：

　　《基于几率波探测下的量子雷达系统原理》谭宏，赵明旺，张国安

　　《量子雷达探测目标的基本原理与进展》江涛，孙俊

(责任编辑：刘盛钱 UN649)
2016-09-07 13:26:17
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