We compare the efficiency of different matrix product state (MPS) based methods for the calculation of two-time correlation functions in open quantum systems. The methods are the purification approach [1] and two approaches [2,3] based on the Monte-Carlo wave function (MCWF) sampling of stochastic quantum trajectories using MPS techniques. We consider a XXZ spin chain either exposed to dephasing noise or to a dissipative local spin flip. We find that the preference for one of the approaches in terms of numerical efficiency depends strongly on the specific form of dissipation.

中文翻译：

---

开放量子系统中两次相关函数的矩阵乘积状态法数值评估：比较

我们比较了基于不同矩阵乘积状态（MPS）的方法在开放量子系统中两次相关函数的计算效率。这些方法是基于MPS技术的随机量子轨迹的蒙特卡罗波函数（MCWF）采样的纯化方法[1]和两种方法[2,3]。我们考虑了XXZ自旋链，要么暴露于相移噪声，要么暴露于耗散的局部自旋翻转。我们发现，就数值效率而言，对一种方法的偏好在很大程度上取决于耗散的特定形式。