【作者】 刘海龙；

【导师】 王海；

【作者基本信息】 山西大学 ， 原子与分子物理， 2013， 硕士

【摘要】 近年来,量子信息存储是量子信息科学领域的一个研究热点[1-3],利用电磁感应透明(EIT)效应将光量子信息存储到原子介质中更是引起了国内外科学界的普遍关注[4-6]。在这个领域,弱信号光的探测是一个不可回避的问题,如何滤除背景光对信号光的影响,改善接收系统的信噪比与灵敏度在整个系统中起着至关重要的作用。所以,我们需要在探测系统中通过滤波器件去消除背景光的干扰。而在原子存储实验中,背景光主要是耦合光,信号光和耦合光的频率往往相差几个GHz[7-9],这样就要求滤波器件对信号光有较高的透射率和较窄的带宽。本文首先简单介绍EIT动力学过程和利用EIT实现的光量子信息的存储与释放,并提出在提取存储信号的过程中遇到的问题；然后分别介绍了我们研制的两种滤波原理不同的滤波器：Rb原子滤波器和F-P干涉滤波器。通过理论计算和实验研究,对两种滤波器的优缺点进行分析,并总结出两种滤波器的不同适用范围。本文介绍的工作具体包含以下内容：(1)简单介绍EIT动力学过程和俘获冷原子的基本过程,并详细介绍了利用EIT效应实现的光量子信息存储与释放实验。在实验中发现：耦合光和探针光传播方向之间的角度会显著地影响光量子信息在冷原子介质中的存储时间,两束光的重合度越高,存储寿命越长,存储效率越高,但这样却给弱存储信号的提取带来了困难,对实验结果的分析带来一定的影响。(2)采用合适的能级结构对Rb原子滤波器作理论计算,并对计算结果进行拟合,分析其可能性,然后通过实验验证其可行性。实验中,将一束激光调谐到Rb原子D2线的F=1→F’=2共振吸收线上,使其泵浦Rb原子,实现原子布居极化(即将Rb原子制备到能级F=2上)。当一束信号光反向穿过该介质时,若信号光频率调谐到原子“吸收窗口”(D1线F=2→F’=1),该介质对信号光大量吸收,信号光透射率仅为0.14%；若信号光频率调谐到原子“透明窗口”(D1线F=1→F’=1),信号光透射率高于47.4%。这种极化的原子介质可以用来做光学滤波器。(3)简单介绍了F-P干涉滤波器的基本原理和结构,对其重要性能指标作了一定的分析,在理论上得出F-P干涉滤波器的重要参数,并详细介绍了我们研究小组曾经使用的和改进的F-P干涉滤波器的结构。实验上,采用厚度为5mm、两表面反射率为50%(795nm)的平面石英玻璃做标准具,通过精确控温,使其对探针光具97%透射率,同时对耦合光透射率为10%左右,1小时内透射率的波动小于1%。可用于光量子信息存储与释放实验中的滤波要求。更多还原

【Abstract】 In recent years, quantum information storage is a hot research topic in the field of quantum information science, using electromagnetically induced transparency (EIT) effect of optical quantum information storage to atomic medium is more universal attention caused the scientific community at home and abroad. In this field, the detection of weak signal light is an unavoidable problem, how to eliminate the effect of background light on signal light, improving the signal-to-noise ratio and the sensitivity plays a vital role in the whole system. Therefore, we need to eliminate the interference of background light by inserting filter device in the detection system. In the atomic storage experiment, the discrepant frequency between signal light and the background light is about several GHz, that means we need the filter has high transmissivity and narrow bandwidth to signal light.This paper first introduces the dynamic-process of EIT effect and the storage and release of quantum information by EIT effect, and put forward the problem in extracting the storage signal; then introduces the two kinds of filter with different filter theory:Rb medium filter and F-P interference filter. Through the theoretical calculation and experimental research, analysis the advantages and disadvantages of two kinds of filter, and sum up the different application range of them. This paper introduces the concrete work includes the following content:(1) We simply introduce the basic kinetics process of the EIT and the cold atoms trapping, and present the detail of the storage and release of optical quantum information by EIT effect. We have found that in the experiment:the angle of the propagation direction between the coupling light and the probe light will affect the time of the quantum information storage in the cold atomic medium significantly, the higher of the overlap degree, the longer storage life will be, as well as a higher storage efficiency, but it is difficult in extracting weak storage signal and analyzing of experimental results.(2) We select the appropriate level structure for theoretical calculations of the Rb medium filter, analyze the possibility by fitting the calculated results, and then verify its feasibility by experiments. In the experiment, the signal light and the pump light goes through the high temperature Rb medium, and we studied the absorption and transmission of the signal light which is locked in different transition line. It turned out that:the pump light with its frequency tuned to the resonance transition F=1→F’=2of Rb medium D2line pump the atom by appropriate temperature control structure, so the atom is prepared to energy level F=2, such polarized atoms can bring about the selective transmission of the probe light and the coupling light in the experiment of the storage and release of optical quantum information, and meet the filtering requirement.(3) We introduce the fundamental principle and the structure of the F-P interference filter briefly, and make some analysis of its important performance index, and then derive the important parameters of the F-P interference filter in theory, and present the detail of the F-P interference filter structure we have used and improved. It turned out that, the stability of improved structure F-P interference filter’s mechanical structure and temperature is improved obviously. In order to meet the requirements of filter in the storage and release of optical quantum information on the single photon level, we put forward the concept of F-P etalon filter system, and demonstrate effectiveness of the filter system by experimental test.更多还原