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Weak Signal Detection----New Theory and Experiment

Weak Signal Detection—New theory and Experiments

 

In many research and application fields, especially in defense science and technology, the accurate measurement of weak signal is involved. To our knowledge, ultra-weak light imaging and photon counting imaging have been widely used in the fields of quantum optics, astronomy, military, remote sensing, and biological microscopy. For example, 3D laser radar based on photon counting has been applied in the unmanned aerial vehicle (UAV) in the United States. In the fluorescence microscope and other biomedical instruments, “ultra-weak light imaging system” is indispensable. The Nobel Prize in chemistry 2014 was awarded jointly to Eric Betzig, Stefan W. Hell and William E. Moerner “for the development of super-resolved fluorescence microscopy”, which realizes imaging in a very small area, and puts forward a higher demand in imaging sensitivity. Now in the field of weak light imaging or photon counting, the imaging sensitivity of ICCD and EMCCD is close to single photon level. These array detectors have high gain, and their imaging sensitivity is determined by the sensitivity of the response of each pixel of detectors. The detector with capability of true single photon detection should be the counter-type photomultiplier tube (PMT) and the avalanche photodiode (APD). Especially the latter can work in the Geiger-mode, with higher sensitivity, shorter response time, and lower dark counts. Since the single photon is the smallest energy unit of quantum mechanics, the present high sensitive detectors are usually equipped with the function of single photon detection, and thus the sensitivity of these kinds of devices is close to the limit.

However, it is very difficult to develop “ultra-weak light detection” for the following three reasons: a) How to eliminate the noise. Any system has the noise, and the measured signal is very weak. Therefore, how to extract the useful signal that is submerged in the noise is of great significance. In the photoelectric detection system, to suppress the noise that comes from the signal light, background light, photoelectric detector and electronic circuit, the traditional methods include reasonable compressing visual field, and selecting appropriate filters, spatial filters and electronic filters. However, when the signal is very weak, or completely submerged in the noise, the traditional method is not effective. Thus, it is necessary to develop a new method to extract the weak signal from the noise. b) How to improve measurement accuracy. c) How to shorten the measurement time. It was difficult to solve these problems a few years ago, but now there are some available techniques to combine: compressed sensing (CS) theory and single photon detection technology, as well as other relevant theoretical advances, experimental methods and the improved devices. Our research aims to realize ultra-weak signal detection by applying the latest theories of modern mathematics, quantum physics, quantum detection technology, and cross fusion.

By the combination of our former research work in quantum physics, electromagnetic theory, CS theory, quantum information and single photon detection technology, we can greatly extend advantages of our research, such as super-sensitivity and low dimension measurements. The development of the research direction is not only beneficial to the development of the physical discipline itself, but also to the development of the national application demands and national defense needs.

The School of Physics, Beijing Institute of Technology (BIT) has been engaged in CS quantum state tomography, quantum imaging and ultra-weak light detection, complex electromagnetic theory, gravitational theory and the study of protein structure in the last five years. We have undertaken a number of research projects, including the National Key Scientific Instrument and Equipment Development Project of China, the National High Technology Research and Development Program of China (863 projects), National Natural Science Foundation of China. We have a long-term cooperation with the Chinese Academy of Sciences to carry out the study of quantum imaging and have accumulated a certain research foundation in the compressive single-pixel imaging, single photon detection technology and etc.

The research fields include:

1) Theory and applications of compressed sensing:

(a) research on CS theory and its optimization algorithms; (b) the applications of CS theory in quantum state tomography and multi-photon entanglement; (c) the research of CS quantum imaging by combining with single photon detection technology;

2) Ultra-weak signal detection and applications, research on applications of quantum detection and CS related areas:

(a) the development and applications of single-photon time-resolved imaging spectrometer---our work focuses on the CS algorithm package research; (b) the study of high resolution infrared imaging; (c) the study of ultra-sensitive telescope;

3) Electromagnetic propagation in complex medium and its applications:

(a) the research of electromagnetic propagation in complex medium, including turbulence, plasma, magneto-electric effect, gravitational field and other complex media, and further study of their quantum fluctuations; (b) effects of complex media on weak signal transmission, detection and imaging quality, and the effectsof all kinds of the noise on imaging quality;

4) Protein structure, folding and dynamics:

(a) expanding the gauge invariance of quantum field and string theory to the study of proteins, and developing an accurate model of protein structure and a folding dynamic method; (b) applications of the calculation and prediction of protein structure, ways of directly calculating energy function parameters from the amino acid sequence of the protein, then develop a new technique to predict a protein structure, and set up a database of soliton classification of protein structure; (c) applications of CS theory in prediction of protein structure; (d) study on pathogenic mechanism with protein misfolding diseases;

5) Theory of gravitation and Cosmology:

(a) the study of cosmology related fields, especially the dark energy cosmology, the modified gravity theory, inflationary cosmology, observational cosmology, quantum gravity, particle physics, cosmological model; (b) study on the model construction, data fitting and data analysis of astronomical observations, analysis of dynamics system related with dark energy and the modified gravity theory; (c) the use of astronomical data including supernova, cosmic microwave background radiation, large scale structure, gamma ray bursts.

The implementation of these fields is based on CS theory and its applications in quantum physics, and can be easily extended to related disciplines, which leads to wider application prospects. It promotes a distinct combination of science and technology in physics, optoelectronics, optical engineering, information and biological science, with the characteristics of interdisciplinary integration features. It can meet national strategic demands and defense requirements through both fundamental physics and applied mathematics research. Therefore, the direction of our research makes full use of the military application background of BIT in engineering and technology and the ultra-weak signal detection technique with national defense features to support the development of applied research, and national defense technology.

Release date:2015-10-27