Effects of Imperfect Observation on Quantum State Estimation

Imperfect observation is an indispensable but often neglected part for practical measurement. In this work, we mainly investigate its effect upon estimating quantum states by focusing on several specific examples. It is shown that the accuracy of the quantum state estimation will be greatly degraded in the presence of imperfect observation. In order to reduce its destructive influence, a cautious estimation method and the adaptive measurement strategy are attempted. However, it turns out that both of the methods cannot always overcome the performance deterioration due to the observation error. The results warn us that we have to seriously deal with the problem of imperfect observation in practical quantum information processing.