NMR量子信息处理中弛豫研究的归一化方法
Normalization procedure for relaxation studies in NMR quantum information processing
摘要：
NMR量子信息处理研究依赖于代表所谓的伪纯态（PPS）的密度矩阵的重构。PPS状态的初始纯部分在计算过程中经历酉和非酉（弛豫）变换，导致“纯度损失”，直到达到平衡。此外，在弛豫时，核极化随时间变化，这是在比较不同时刻的密度矩阵时必须考虑的事实。当松弛存在时，试图使用固定时间的归一化程序，会导致矩阵总体上的各种异常。在本文中，我们提出了一种方法，考虑到时间依赖性的归一化因子。从偏差密度矩阵的一般形式导出了弛豫初纯态的表达式。以出现猝死现象的伪纠缠态的纠缠度弛豫实验和伪猫态的Wigner函数弛豫实验为例说明了该方法的有效性。
英文摘要：
NMR quantum information processing studies rely on the reconstruction of the density matrix representing the so-called pseudo-pure states (PPS). An initially pure part of a PPS state undergoes unitary and non-unitary (relaxation) transformations during a computation process, causing a "loss of purity" until the equilibrium is reached. Besides, upon relaxation, the nuclear polarization varies in time, a fact which must be taken into account when comparing density matrices at different instants. Attempting to use time-fixed normalization procedures when relaxation is present, leads to various anomalies on matrices populations. On this paper we propose a method which takes into account the time-dependence of the normalization factor. From a generic form for the deviation density matrix an expression for the relaxing initial pure state is deduced. The method is exemplified with an experiment of relaxation of the concurrence of a pseudo-entangled state, which exhibits the phenomenon of sudden death, and the relaxation of the Wigner function of a pseudo-cat state.
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