Characterization of systematic errors in direct quantum state measurements

研究了量子控制相互作用框架下直接态测量（DSM）的系统操作误差。在该方案中，目标系统由量子位探针控制，并在共轭基上进行后选择;控制量子位探针的结果可以被测量并从估计状态中取出。我们考虑了两种类型的相互作用：（i）反量子控制相互作用（I型）和（ii）任意强相互作用（II型），它等价于von Neumann相互作用，我们发现I型的系统误差比II型小，这意味着更高的精度。对于相同的置信水平，类型I在置信区域中具有更高的百分比比率。第一类的系统误差也很好地抵抗了噪声，因为它的保真度在噪声下得到了保护。我们的研究给出了使用量子控制测量方案的量子态层析成像的更好解决方案（优于传统的强测量和弱测量）。此外，它的测量是简单的，适用于高维系统。因此，这种方法可能是一个潜在的候选人，进一步表征大系统的属性。

We investigated the systematic operational errors in the direct state measurements (DSM) with a quantum controlled interaction framework. In this scheme, a target system is controlled by a qubit probe and postselected onto a conjugate basis; the outcomes of the control qubit probe can be measured and taken out of the estimated state. We have considered two types of operational interaction: (i) invert quantum controlled interaction (type-I) and (ii) arbitrary strong interaction (type-II), which is equivalent to a von Neumann interaction.We found that type-I gives lower systematic error than type-II, which means more accuracy. For the same confidence level, type-I has a higher ratio into percentage in the confidence region. The systematic error in type-I is also well against the noise as its fidelity is protected under the noise.Our study gives a better solution for quantum state tomography using the quantum controlled measurement scheme (better than conventional strong measurements and weak measurements.) Furthermore, its measurement is simple and applicable to high-dimension systems. This method, thus, could be a potential candidate for further characterizing the properties of large systems.