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arXiv 1402.4553quant-ph
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线性无关纯态的最小误差判别:POVM的解析性质

Minimum Error Discrimination of Linearly Independent Pure States: Analytic Properties of POVM

Tanmay Singal, Sibasish Ghosh

摘要:

线性无关纯态最小误差判别的最优化条件包括两类:秩一投影测量空间上的平稳条件和全局最大化条件。一个离散数量的射影测量将解决前者,其中一个唯一的将解决后者。在三个真实的线性独立的纯态的情况下,我们表明,驻定条件转化为一个系统的多项式(非线性)方程在三个变量,从而解释了为什么它是如此难以获得一个封闭形式的解决方案的最佳POVM。此外,我们的方法表明,由于LI纯态的系综是作为一些独立参数的平滑函数而变化的,因此最佳POVM也将作为相同参数的函数而平滑地变化。利用隐函数定理,我们得到了一种从已知的例子(例如纯正交态)到同一Hilbert空间中任意线性无关的纯态系综的求解方法。通过使用RK4求解一阶耦合非线性微分方程,发现所得误差在RK4误差性能范围内。

英文摘要:

The optimization conditions for minimum error discrimination of linearly independent pure states comprise of two kinds: stationary conditions over the space of rank one projective measurements and the global maximization conditions. A discrete number of projective measurments will solve th former of which a unique one will solve the latter. In the case of three real linearly independent pure states we show that the stationary conditions translate to a system of simultaneous polynomial (non linear) equations in three variabes thus explaining why it's so difficult to obtain a closed-form solution for the optimal POVM. Additionally, our method suggests that as an ensemble of LI pure states is varied as a smooth function of some independent parameters, the optimal POVM will also vary smoothly as a function of the same parameters. By employing the implicit functions theorem we exploit this fact to obtain a technique to find the solution of MED of LI pure states by dragging the solution from a known example (say, pure orthogonal states) to any general linearly indepenent ensemble of pure states in the same Hilbert space. By employing RK4 to solve the first order coupled non-linear differential equations find that the resulting error is within the RK4 error performance.

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