Preparation And Application Of High Efficiency Entangled Sources

Quantum entanglement reveals the coherence,probability and spatial non-local nature of quantum mechanics,and is the most peculiar existence in quantum theory.At present,quantum entanglement has been widely used in many fields such as quantum communication,quantum metrology,quantum computing and quantum ranging.Therefore,it is important to study the preparation of efficient entangled sources.Radiometric calibration is an important part of quantum metrology.With the development of remote sensing technology,the requirements for calibration accuracy have gradually increased.However,traditional calibration techniques are difficult to continue to improve accuracy.The new radiometric calibration method based on correlated photons provides a new direction of development because it does not depend on any primary standards and transmission chains.Firstly,the paper introduces three common methods for preparing quantum entangled sources,and mainly emphasizes the method of spontaneous parameter down conversion.The entangled two-photon pair of 1550 nm and 460 nm is prepared by the I-type phase matching technique of BBO crystal.Then we realized the calibration of the ID220 single photon detector produced by IDQ of Switzerland.On the basis of previous work,we analyzed the influencing factors such as background noise and filter permeability during the experiment,and optimized the experimental results.Considering the shortcomings of the above experimental system,we designed a quantum efficiency calibration scheme for single photon detector based on quasi-phase matching technology from the selection of pump light,crystal design,photon detection and signal acquisition.At this time,a PPLN crystal having the polarized period of 7.4?m reacted with the pump light having a wavelength of 532nm to generate entangled light of 1550 nm and 810 nm at the temperature of 118“C.This not only exerts the maximum nonlinear coefficient d33 of the crystal to improve the efficiency of the conversion.At the same time,the use of the collinear mode makes it extremely easy to determine the exit direction of the photons.We confirmed the feasibility of using the quasi-phase matching technique to prepare high-efficiency entangled sources by comparing the count values of the 1550 nm channel obtained in two cases.