Construct And Optimization Of Cold Rubidium Atoms’ Quantum Information Storage Imaging Systems

With the development of technology, communications security began to receive widespread attention. Because of its high efficiency and absolute security of transmitted information, quantum communication develops rapidly. Due to absorption loss by optical fiber and atmospheric loss during transmission, the distance of single-stage quantum communication is short. The quantum secret communication relay transmission can be achieved using quantum memory, then breaks communication distance limitation. From the study of quantum memory at home and aboard in recent years, although the quantum memory has made a certain degree of process, the most are still limited by the short storage time. The experimental system built by our team is based on the ensemble quantum memory of 87 Rb cold atomic, and the experimental objective is to achieve a long lifetime quantum storage of more than 16 s.The main work of this thesis is to complete the experimental construction of the quantum optical storage system and optimize the experimental parameters which affect the trapped cold atoms. On basis of preliminary experiments, we processed the EIT(electromagnetically induced transparency) and Autler-Townes splitting of cold atoms. The research is divided into the following parts:First of all, the recovery of experimental optical path and construction of imaging optical path were completed, and the symmetry of six magneto-optical trap laser beams was optimized. The strict correspondence between the light field and the magnetic field center could be made by optimizing the magneto-optical trap so that the maximum number of atoms could be achieved to improve the stability of atoms number.Secondly, the magneto-optical trap for trapping atoms which affect the number of experimental parameters were studied. First we calibrated magnification of experimental CCD and measured atoms using three experimental methods of calibration. Finally, the experimental parameters affecting the number of atoms were optimized, and the optimal parameters of our laboratory cooling laser were reached: detuning was-16 MHz, gradient magnetic field was 13.2G/cm, each beam of cooling and repumping power were 2.445mW/cm2、 0.399mW/cm2. Using the blue LED(Light-Emitting Diode, LED), irradiation in glass Pyrex chamber adsorbed atoms fall on the glass, increasing the concentration of atoms.Finally, based on the optimization of experimental parameters, we conduct a preliminary experiment on electromagnetically induced transparency, dispersion and AT splitting, and we got the dispersion curve of EIT and AT splitting of cold atoms. The realization of magneto-optical trap lays a decent foundation for the goal of long lifetime quantum memory in the next step.