Minimax Strategy of Optimal Unambiguous State Discrimination

In this paper, we consider the minimax strategy to unambiguously discriminate two pure nonorthogonal quantum states without knowing a priori probability. By exploiting the positive-operator valued measure, we derive the upper bound of the minimax measurement of the optimal unambiguous state discrimination. Based on the linear optical devices, we propose an experimentally feasible scheme to implement a minimax measure of a general pair of two nonorthogonal quantum states.     

纠缠态表象在热场动力学中的应用

大多数量子系统都与外界环境之间存在某种热交换或热纠缠,受量子光学双光子纠缠态表象启发,本文将建立热纠缠态表象．根据Takahashi与Umezawa提出的热场动力学理论,热场混合态可以等效为一个量子纯态．因此,任意量子态在环境温度不为零（T≠0）时,系综期望值可以等效成对量子纯态的平均值．在温度趋向于无穷大时,可以得到热真空态的极限形式．类似于相干态,利用平移算符对热真空态极限形式做平移操作后,即可得到热相干态（也称为热纠缠态）．热纠缠态表象可以将密度算符ρ=|m〉〈n|中的左矢部分转化为与环境有关的ρ=|m〉〈n|,从而可以使讨论量子态在热环境的演化变得方便快捷．