Xin Tao, Pedernales Julen S, Lamata Lucas, Solano Enrique, Long Gui-Lu
State Key Laboratory of Low-dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, 100084, China.
Tsinghua National Laboratory of Information Science and Technology, Beijing, 100084, China.
Sci Rep. 2017 Oct 9;7(1):12797. doi: 10.1038/s41598-017-13037-4.
We measure multi-time correlation functions of a set of Pauli operators on a two-level system, which can be used to retrieve its associated linear response functions. The two-level system is an effective spin constructed from the nuclear spins of H atoms in a solution of C-labeled chloroform. Response functions characterize the linear response of the system to a family of perturbations, allowing us to compute physical quantities such as the magnetic susceptibility of the effective spin. We use techniques exported from quantum information to measure time correlations on the two-level system. This approach requires the use of an ancillary qubit encoded in the nuclear spins of the C atoms and a sequence of controlled operations. Moreover, we demonstrate the ability of such a quantum platform to compute time-correlation functions of arbitrary order, which relate to higher-order corrections of perturbative methods. Particularly, we show three-time correlation functions for arbitrary times, and we also measure time correlation functions at fixed times up to tenth order.
我们测量了两能级系统上一组泡利算符的多时间关联函数，这些函数可用于获取其相关的线性响应函数。该两能级系统是由(^{13}C)标记的氯仿溶液中氢原子的核自旋构建而成的有效自旋。响应函数表征了系统对一系列微扰的线性响应，使我们能够计算诸如有效自旋的磁化率等物理量。我们使用从量子信息中导出的技术来测量两能级系统上的时间关联。这种方法需要使用一个编码在(^{13}C)原子核自旋中的辅助量子比特以及一系列受控操作。此外，我们展示了这样一个量子平台计算任意阶时间关联函数的能力，这些函数与微扰方法的高阶修正有关。特别地，我们展示了任意时刻的三次关联函数，并且我们还测量了固定时刻高达十阶的时间关联函数。
