In classical physics, the detection of any physical quantity is accompanied by noise, including the classical noise of the system and quantum noise, which limits the detection accuracy. Among them, the classical noise mainly comes from technical defects, the advantages and disadvantages of instruments and other factors. With the development of science and technology, the classical noise of the system is greatly reduced and can often be ignored. Therefore, quantum noise determined by quantum mechanical properties gradually becomes the main source of noise. The squeezed light source has the quantum property that a certain orthogonal component can be lower than the shot noise limit, which breaks through the standard quantum noise limit and further improves the detection accuracy. As a kind of non-classical light, the squeezed state has great application potential in the field of quantum optics. Based on the stable working squeezed light prepared in the early stage, and combining with the theory, experiment and key technology of Professor Bi over 20 years, we have developed a set of instrumentized short-range quantum infrared detector. Special design is made in light source, detection system, pattern matching, phase locking, structure design and packaging, which can effectively improve detection accuracy and imaging quality in the range of 0.5m-9m, and then used in light source correction such as transverse displacement and tilt measurement of light beam and various detection under special conditions such as weak light.
In classical physics, the detection of any physical quantity is accompanied by noise, including the classical noise of the system and quantum noise, which limits the detection accuracy. Among them, the classical noise mainly comes from technical defects, the advantages and disadvantages of instruments and other factors. With the development of science and technology, the classical noise of the system is greatly reduced and can often be ignored. Therefore, quantum noise determined by quantum mechanical properties gradually becomes the main source of noise. The squeezed light source has the quantum property that a certain orthogonal component can be lower than the shot noise limit, which breaks through the standard quantum noise limit and further improves the detection accuracy. As a kind of non-classical light, the squeezed state has great application potential in the field of quantum optics. Based on the stable working squeezed light prepared in the early stage, and combining with the theory, experiment and key technology of Professor Bi over 20 years, we have developed a set of instrumentized short-range quantum infrared detector. Special design is made in light source, detection system, pattern matching, phase locking, structure design and packaging, which can effectively improve detection accuracy and imaging quality in the range of 0.5m-9m, and then used in light source correction such as transverse displacement and tilt measurement of light beam and various detection under special conditions such as weak light.
High resolution, high signal-to-noise ratio and high sensitivity have always been the goals and technical bottlenecks of detection, precision measurement and imaging. Quantum detection technology is one of the disruptive cutting-edge technologies in the world. Quantum information technology is introduced into the field of classical detection, hoping to solve the difficult technical bottleneck on the basis of classical physics. Compared with traditional detection methods, quantum detection has higher sensitivity, can receive weaker signals, requires lower transmission power, and has stronger anti-interference ability. In terms of precision measurement, the characteristics of quantum mechanics are used to make the measurement accuracy break through the classical physical limit, and then improve the measurement accuracy of the detection system. But with the development of remote sensing technology and people demand for long distance detection, we completed in the early completed close quantum detection, combined with remote sensing technology, the quantum squeezed light into the receiving system, using quantum phase-free amplification technology, make up for the low efficiency of the detector, make its imaging results close to the ideal detector. We designed a set of quantum squeezing light preparation, emission /receiving system, quantum enhancement module, quantum imaging system, balance homodyne detection system, data processing system, central control system in one of the remote quantum infrared detector, effective detection distance up to 100 meters, at the same time achieve high resolution imaging, the same environment and classical laser imaging resolution increased by 1 to2 times. In March 2000, Professor Siwen Bi conducted the exploration and research on quantum remote sensing. At the beginning of 2001, Professor Siwen Bi first put forward the concept of quantum remote sensing at home and abroad. In the past 20 years, through three stages of basic theoretical scientific experiments and key technologies, we have overcome many difficulties in theoretical research scientific experiments and key technologies ,and achieved breakthrough progress and innovative results, which have laid a key foundation for the follow-up quantum laser radar quantum remote sensing products.
As a combination of laser technology and modern photoelectric detection technology, lidar (laser radar) has notable advantages compared with traditional radar such as high resolution, strong anti-interference ability, and good low-altitude detection performance. However, with continuous application in aerospace, military, artificial intelligence and other fields, lidar has reached the limits of classical physics and can’t meet the requirements in detection, measurement and imaging. In order to break the bottleneck, worldwide researchers have developed a new type of radar-quantum lidar, which is based on the combination of traditional radar technology and quantum information technology. Its main principle is to get imaging through squeezed light that is below the noise limit of classical physics and then manipulated by the quantum state to achieve imaging with higher quality. Quantum lidar in the paper injects quantum squeezed light to receiver end and uses quantum phase-sensitive amplifier technology to compensate the photon loss that caused by insufficient quantum power to further improve resolution. In the squeezed light, the generation of quantum squeezed light and detection theory are studied, the resonant cavity locking principle and balanced homodyne detection principle are analyzed, and a mode cleaner with narrow line width is designed to improve beam transverse mode quality of laser and filter high frequency noise. In order to reduce quantum noise and improve resolution, quantum lidar imaging system is developed and the theoretically derivation and numerical simulation results show that the resolution of quantum lidar imaging is 1.71 times higher than that of lidar imaging.
Based on the basic theory, information mechanism and imaging experiment of quantum remote sensing, quantum spectral imaging and quantum detection and identification, as well as the production of principle prototype, the author conducted researches on high-sensitivity target detection of infrared optical quantum squeezing that can breakthrough quantum noise limit, high resolution imaging technical solutions and imaging principle experiment, focusing on realizing of high sensitivity long-range target detection, system composition and working principle of high-resolution imaging experimental device, infrared quantum optical squeezed light preparation and injection, and quantum noiseless amplifier, aiming to resolve relevant crucial problems, which provide technical basis for the production of engineering prototype and its experimental device. Besides, based on the project assignment, the paper firstly introduces research status at home and abroad, the development tendency, and research significance and necessity, then it emphasizes the research target, research content and key technical index, as well as the overall technical solutions, solutions and feasibility analysis for key technologies. Finally, it summarizes benefit analysis, project arrangement and outcome forms.
According to the Heisenberg uncertainty principle, the precision of any physical quantity measurement is limited by quantum fluctuation in general, which leads to the so-called standard quantum limit (SQL). The SQL can be beaten by using squeezed light, hence enhancing the measurement accuracy. Squeezed light is a typical nonclassical light, it exhibits reduced noise in one quadrature component. Since Caves proposed the scheme of phase measurement enhancement with squeezing, squeezed light has been used to enhance measurement precision in many areas. This review focuses on the following four kinds of precision measurements based on squeezed light: the measurements of relative phase, small lateral displacement and tilt, magnetic field, and clock synchronization. For all of these measurements, vacuum squeezing has been used to enhance measurement precision, while the types of squeezing (squeezing angle, transverse mode, polarization etc.) are different. For phase measurement, quadrature squeezing is injected into the conventionally unused input port of Mach-Zehnder interferometer (MZI) or Michelson interferometer (MI). For displacement or tilt measurement, a vacuum squeezing beam of a special transverse mode is coupled into an intense coherent beam, yielding a spatial-squeezed light whose transverse position or tilt angle noise is lower than that of a classical light beam. Based on the Faraday effect of polarization rotation, the magnetic field can be detected precisely. The precision can be increased further by using the polarization squeezing. The polarization squeezing can be generated by coupling two orthogonal polarized beams together, a coherent beam and a vacuum squeezed beam. Various polarization squeezing can be illustrated on the Poincaré sphere. Finally, in the clock synchronization based on the optical frequency comb, squeezed light can be used to enhance the time measurement precision. A theoretical scheme with multimode squeezing of supermode (a kind of mode describing the frequency mode of a pulse laser beam) is introduced. The squeezing has extensively been applied into the quantum precision measurements such as gravitational wave detection as well as biological measurement and will play a more important role in the near future.
Lidar (laser radar) offers advantages over conventional radar in terms of higher resolution, greater anti-interference capability and ultra-low altitude detection performance. However, Lidar has now reached a bottleneck in terms of detection range and is no longer able to correctly identify targets beyond 500 meters, thus failing to meet the requirements for detection, measurement and imaging. To break this bottleneck, we have developed a Quantum Lidar with a detection range of up to one kilometre, which is based on a quantum vacuum squeezed laser and can compress the photon fluctuation by 5.6dB in the vacuum state through quasi-phase matching in non-linear crystals, reducing the quantum noise of laser which accounts for 73% of the lidar, thus reducing the overall noise of the quantum lidar by 3.27dB and improves the phase stability of the laser (from 10 minutes to more than 120 minutes) to achieve higher accuracy measurements, with a Signal-Noise Ratio (SNR) twice that of conventional lidar, and therefore a sensitivity twice as high. The basic technical implementation is to use a 20W power 1064nm wavelength continuous wave laser (CW, M2 less than or equal to 1.05) to irradiate a target located one kilometre away. By detecting a very weak reflected laser (power=10μW ± 5μW) which is exponentially attenuated by distance, We use noiseless amplification by a quantum vacuum-squeezed laser with the same power magnitude to obtain a higher power (7dB amplification) and higher signal-noise ratio (4.77dB SNR improvement). A reflective lens set (250mm aperture) of our design is used to receive the laser diffusion due to the 4mrad transmission angle of one kilometre. In the squeezed laser system, the resonant cavity locking efficiency is improved to 99.7%, and the re-locking time is less than 0.3s, it is directly switchable with the balance homodyne detection system. The mode cleaner improves the transverse mode quality(the mode bandwidth is reduced by 67%) while filtering high-frequency noise. The quantum lidar imaging system has been developed, and the experimental results show that the resolution of the laboratory-simulated long-range decay experiment is 3 times higher than that of traditional lidar is a promising development. This means that the system can detect and image smaller objects and features with greater accuracy and precision. The use of a self-developed quantum enhancement algorithm to obtain a 5 times higher contrast lidar image is also a significant improvement, and the use of a quantum denoising algorithm to reduce graphic distortion and image scatter caused by atmospheric pollution and environmental interference is a critical development. These issues can significantly degrade the quality of lidar images, so being able to mitigate their effects is a significant step forward. Through a self-developed LiDAR 3D reconstruction algorithm, the reconstruction efficiency is increased by 3 times and the resolution is increased by 2.5 times, which means that the reconstructed 3D model is faster, more detailed and accurate. In the future, based on one kilometre's work, achieving a quantum lidar with a detection distance of 10, 20 or even 50 kilometres with much clearer images would require advancements by steadily improving the resolution, improving the signal-noise ratio of the system, improving the laser power and optimising the algorithm.
Quantum imaging can be defined as an area of quantum optics that investigates the ultimate performance limits of optical imaging allowed by the quantum nature of light. Quantum Imaging techniques possess a high potential for improving the performance in recording, storage, and readout of optical images beyond the limits set by the standard quantum level of fluctuations known as the shot noise. This talk aims at giving an overview of the fundamentals of Quantum Imaging as well as its most important directions. We shall discuss generation of the spatially multimode squeezed states of light be means of a travelling-wave optical parametric amplifier. We shall demonstrate that this kind of light allows us to reduce the spatial fluctuations of the photocurrent in a properly chosen homodyne detection scheme with a highly efficient CCD camera. It will be shown that using the amplified quadrature of the light wave in a travelling-wave optical parametric amplifier, one can perform noiseless amplification of optical images. We shall provide recent experimental results demonstrating a single-shot noiseless image amplification by a pulsed optical parametric amplifier. One of important experimental achievements of Quantum Imaging, coined in the literature as quantum laser pointer, is a precise measurement of position and transverse displacement of a laser beam with resolution beyond the limit imposed by the shot noise. We shall describe briefly the idea of the experiment in which the transverse displacement of a laser beam was measured with resolution of the order of Angstrom. The problem of precise measurement of transverse displacement of a light beam brings us to a more general question about the quantum limits of optical resolution. The classical resolution criterion, derived in the nineteen century by Abbe and Rayleigh, states that the resolution of an optical instrument is limited by diffraction and is related to the wavelength of the light used in the imaging scheme. However, it was for a long time recognised in the literature that in some cases when one has some a priori information about the object, one can improve the resolution beyond the Rayleigh limit using the so-called super-resolution techniques. As a final topic in this talk, we shall discuss the quantum limits of optical super-resolution. In particular, we shall formulate the standard quantum limit of super-resolution and demonstrate how one can go beyond this limit using specially designed multimode squeezed light.