Quantum radar is a long-distance sensor system, which uses the quantum effect of electromagnetic waves to detect targets at a long distance. Compared with traditional radar, quantum radar emits a pulse signal composed of a small number of photons; The interaction between signal photon and target follows the law of quantum electrodynamics, and the scattering process is described by quantum field theory. At the receiving end, the photon detector is used for burst reception, and the target information in the photon state of the echo signal is obtained by using quantum system state estimation and measurement technology.
According to the different quantum states emitted by quantum radar transmitter, it can be divided into single photon quantum radar and entangled photon quantum radar. The single photon detection quantum radar system emits non-entangled light quantum States, and its working mode is similar to that of classical radar. The quantum radar transmitter emits a single photon to the target, which is reflected by the target and then received and detected by the radar receiver. Single photon detection is an ideal detection scheme, which has the advantage of almost no interference and the disadvantage of being difficult to realize.
Quantum entanglement radar system generates an entangled photon pair by entanglement and superposition of photon quantum states, one of which is sent to the target and the other is still in the receiver of radar system. Based on the correlation characteristics contained in entanglement, the target detection is realized by comparing the coincidence degree between the reflected radiation photons of the target and the photons inside the radar. Through quantum entanglement, quantum radar can enhance the target detection ability and give full play to its greatest advantages. Therefore, quantum entanglement radar has attracted more attention and is one of the main development directions of quantum radar in the future.
The start of the research project of American government and the participation of large military enterprises push the research of quantum radar to a new height, which proves that quantum radar has broad application prospects in the field of national defense security and is a national defense weapon that the United States must strive for.
In terms of theoretical research, foreign quantum radar research began in the 1960s and 1970s. Starting from the study of quantum signals, the research in the fields of quantum measurement, sensing, imaging and detection is carried out, and finally the specific issues such as the working band of quantum radar and the scattering cross section of quantum radar are refined. In 2007, the Advanced Research Projects Agency (DARPA) of the US Department of Defense launched the quantum sensing project and the quantum lidar project, and the research field of quantum radar was formally formed.
In terms of patent application and scheme research, foreign quantum radar patents appeared earlier and entered the patent application period in 2 1 century. According to incomplete statistics, there were 16 patents related to quantum radar in the United States from 2000 to 2008. Many research teams, such as MIT, have proposed quantum radar schemes, mainly including interferometric quantum radar, receiving quantum enhanced lidar and quantum illumination radar. Among many patents, the most representative one is the patent of quantum radar system based on quantum entanglement theory applied by Lockheed Martin in 2005. According to patent data, the latest patent application time for quantum radar in the United States is 20 16 1.
In terms of prototype development, in 20 13, the University of Rochester in the United States and the University of York in the United Kingdom successively developed quantum radar prototypes. The former is an anti-jamming quantum radar, which can easily detect stealth aircraft with little interference. 20 15 British researchers have developed a microwave and light wave dual-cavity converter which can be used in quantum radar.
Quantum radar has super sensitivity. Quantum radar uses quantum entanglement to improve sensitivity, thus identifying small signals in high background noise. Compared with the classical wave remote sensing detection system, the quantum irradiation radar using quantum entangled electromagnetic waves to detect targets can significantly improve the echo signal-to-noise ratio at the radar receiver, and can comprehensively enhance the radar detection of targets.
The future working frequency band of quantum radar is most likely in microwave band, such as X band, which inherits many advantages of microwave, such as microwave photons can penetrate clouds and have all-weather and all-weather working ability. In addition, quantum radar adopts quantum metrology technology, which greatly improves the resolution of radar ranging, angle measurement and imaging. Compared with traditional radar, quantum radar has the advantages of low power consumption, strong anti-interference, long detection distance, high resolution and easy imaging.
In the field of electronic warfare, quantum radar is a revolutionary technology. Because superluminal waves have stronger penetration ability and anti-jamming ability, quantum radar can detect upward stealth flying objects, stealth warships on the surface of the water and underwater submarines. Quantum radar theory has a very long detection distance and can be used for planetary defense and space exploration.
For example, quantum radar can detect stealth targets, leaving stealth aircraft and stealth ships nowhere to hide. Quantum detection is to measure or image objects by using the characteristics of quantum entanglement and superposition. In electronic countermeasure warfare, quantum radar can be unaffected by the false reflection signals from stealth aircraft and ships. According to the photon change of the detected target, the image of the detected target is restored by the signal processing system, and the position and state of the stealth target are determined to realize comprehensive prevention and control and precise strike. In addition, the hidden form of quantum beam used by quantum radar has nothing to do with the propagation medium, and it can freely detect the targets of deep-sea submarines. Quantum radar quantum beam has strong entanglement characteristics, so it has strong anti-interference. Because it will not be affected by nuclear radiation, it is suitable for nuclear war environment. In the event of a nuclear war, if the headquarters uses a quantum radar detection system, the superior performance of its quantum detection system based on quantum entangled state will not be damaged by the interference of atomic bombs, and it can normally accept and launch tracking targets, greatly improving the initiative of battlefield command.