量子态测定中的弱值与近似值
Weak vs. approximate values in quantum state determination
摘要：
我们推广了量子可观测量的弱值的概念，使其涵盖任意的实正算子测度。我们表明，该定义是操作意义上的，它可以在连续测量的量子理论内理解。然后，我们提出了一个详细的分析，最近的实验Lundeen等人。关于重建的状态的光子使用弱测量。我们比较他们的方法与重建方法通过信息完整的相空间测量，并表明它缺乏相空间方法的通用性。特别是，一个完全未知的状态永远不能使用弱测量的方法重建。
英文摘要：
We generalize the concept of a weak value of a quantum observable to cover arbitrary real positive operator measures. We show that the definition is operationally meaningful in the sense that it can be understood within the quantum theory of sequential measurements. We then present a detailed analysis of the recent experiment of Lundeen et al. concerning the reconstruction of the state of a photon using weak measurements. We compare their method with the reconstruction method through informationally complete phase space measurements and show that it lacks the generality of the phase space method. In particular, a completely unknown state can never be reconstructed using the method of weak measurements.
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