【作者】 李雪莲；

【导师】 李军刚；

【作者基本信息】 北京理工大学 ， 物理学， 2016， 硕士

【摘要】 量子参数估计是把量子系统作为探测指针来对物理参数进行测量和估计,在实验和理论上都有重要的意义。真实的量子系统不可避免地会与外界环境产生相互作用,进而产生能量耗散和消相干,此时量子系统的动力学行为需要用量子开放系统理论来描述,所以需要我们在量子开放系统下研究量子参数估计的过程。我们重点研究了非高斯噪声对于参数估计精度的影响,并通过量子费舍尔信息的行为变化来体现。特别地,我们采用自旋为1/2的系统来估计磁场的强度,并且系统分别受到非高斯噪声中的随机电报噪声和有色噪声的影响。首先选取系统的初态,然后把该态置于磁场中,同时它又受到噪声的影响,最终对时间演化后的态进行测量得到磁场的强度。在这个过程中,我们给定了系统的总的哈密顿量,计算得到相应的布洛赫矢量,进而求得在两种噪声下的量子费舍尔信息的表达式。通过模拟和分析两种噪声下的量子费舍尔信息的变化行为,得到了我们的研究结论,并对这一系列的变化行为给出了详细的解释。我们发现,量子费舍尔信息在很大程度上受到非高斯噪声参数的影响。具体来说,对于随机电报噪声的情况,强耦合和弱耦合的条件下都有利于参数估计;而在有色噪声中,参数估计的精度先随?的增加而降低,然后又随?的增加而增加。更多还原

【Abstract】 Quantum parameter estimation uses the quantum system as a probe to measure and estimate the physics parameter,it is important in both experiment and theory.In reality,quantum system is inevitably influenced by the environment and interacts with it.Therefore,it induces the dissipation of energy and decoherence.As a result,we need make use of the quantum open system theory to describe the behavior of the quantum system.Based on these,we study the quantum parameter estimation under the quantum open system and mainly focus on the influence of non-Gaussian noise on the accuracy of the parameter estimation.Meanwhile,it is reflected by the behavior of the quantum Fisher information.Specially,we adopt a spin-1/2 system to estimate the intensity of the magnetic field,meanwhile the system is influenced by the random telegraph noise and colored noise respectively.At first,we choose our initial state and it can make sure the quantum Fisher information of the output state reaches its maximum value.Then the qubit is subjected to the magnetic field and at the same time it interacts with the noise.After some time,we measure the system to get the information about our parameter.In the process,we give the total Hamiltonian of the system and calculate the density matrix of the state,finally we get the analytic expression of the quantum Fisher information under the two noise.Afterwards,we get the behavior of the quantum Fisher information and analyze it at length.We find that the quantum Fisher information is greatly affected by the noise parameter.To be specific,in the random telegraph noise condition,both strong coupling and weak coupling cases are good for the parameter estimation.While in the colored noise case,the accuracy of the parameter estimation decreases with? firstly and then increases with it.更多还原