相干态和压缩真空态的自适应最优估计方法  

Adaptive optimal measurement for the squeezed vacuum and coherent state

作　　者：陈坤[1] 陈树新[1] 吴德伟[1] 杨春燕[1] 王希[1] 李响[1] 吴昊[1] 刘卓崴 

机构地区：[1]空军工程大学信息与导航学院,西安710077

出　　处：《物理学报》2016年第19期79-85,共7页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:61573372)资助的课题~~

摘　　要：针对文献[物理学报65 054203]中量子零拍探测技术测量的输出相位精度与相位自身相关,且对本振光、压缩真空光和相干光的相位有严格要求,在理论上设计了一种相干态和压缩真空态的自适应最优估计方法.首先以纯态的方法推导得到相干态和压缩真空态的量子费舍尔信息,sinh^2r+|α|~2e^(2r).设计了一组能使估计误差达到量子Cramer-Rao下界的最优半正定算子值测量算子,但该测量算子需要精确已知所要估计的相位参数.为此,引入了一种自适应估计方法,通过不断更新测量算子和概率函数,利用最大似然估计器逐渐得到相位参数.经理论证明,该方法能以概率1收敛于相位真值,且能达到量子Cramer-Rao下界.The output phase of the Sagnac interferometer has been measured with quantum balanced homodyne technique when coherent light and squeezed vacuum light are fed into the Sagnac interferometer simultaneously [Chen Kun et al.,Acta Phys. Sin. 65 054203（2016）]. Nevertheless, there exist two deficiencies： 1） the phase sensitivity is related to the phase itself; 2） there are strict requirements for the phases of local oscillator light, coherent light and squeezed vacuum light.For overcoming these deficiencies, an adaptive optimal measurement scheme is suggested for the phase estimation.Firstly, we calculate that the quantum Fisher information（QFI） of the squeezed vacuum and coherent state is sinh^2r＋｜α｜~2e^（2r） by treating them as a quantum pure state, for they satisfy a condition of the quantum pure state, namelyρ（θ） = ρ（θ）~2. The QFI is related to quantum Cramer-Rao lower bound which can be used to evaluate the performance of the estimator. Secondly, we make an analysis of positive operator-valued measure（POVM） and design a set of the optimal measurement operators for reaching the quantum Cramer-Rao lower bound, whereas the optimal measurement operators depend on the true value of the phase which is what we want to estimate. In order to solve the problem and estimate the parameter effectively, an adaptive method is suggested. We set an initial value of the phase parameter to obtain a set of measurement operators which are not optimal at the first step. And then the initial measurement operators are used for POVM and to obtain a conditional probability function, from which we can obtain a new value of the phase with maximum likelihood estimator. Therefore, the measurement operators and conditional probability function will be updated with the new value. As the measurement operators and conditional probability function are updated step by step, we can estimate the value adaptively. In fact, the results of the maximum likelihood estimator will converge at the true value of the phas

关 键 词：量子零拍探测 半正定算子值测量 量子Cramer-Rao下界 最大似然估计器 

分 类 号：O431.2[机械工程—光学工程]