Characterization of systematic errors in direct quantum state measurements

我们用量子控制相互作用框架研究了直接态测量(DSM)中的系统操作误差。在该方案中，目标系统由量子比特探测器控制，并在共轭基础上进行后选择；控制量子比特探测器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操作相互作用：(I)反量子控制相互作用(类型-I)和(Ii)任意强相互作用(类型-II)，这相当于冯·诺依曼相互作用。我们发现，类型-I比类型-II给出的系统误差更小，这意味着更高的精度。对于相同的置信度水平，类型I在置信度区域中具有更高的比率成百分比。类型I的系统误差也很好地抵抗了噪声，因为它的保真度受到噪声的保护。我们的研究为使用量子控制测量方案的量子态层析提供了更好的解决方案(比传统的强测量和弱测量更好)。此外，它的测量简单，适用于高维系统。因此，这种方法可能成为进一步表征大系统性质的潜在候选者。

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.