Meinel Jonas, Vorobyov Vadim, Wang Ping, Yavkin Boris, Pfender Mathias, Sumiya Hitoshi, Onoda Shinobu, Isoya Junichi, Liu Ren-Bao, Wrachtrup J
3rd Institute of Physics, Research Center SCoPE and IQST, University of Stuttgart, 70569, Stuttgart, Germany.
Max Planck Institute for Solid State Research, Stuttgart, Germany.
Nat Commun. 2022 Sep 9;13(1):5318. doi: 10.1038/s41467-022-32610-8.
Conventional nonlinear spectroscopy, which use classical probes, can only access a limited set of correlations in a quantum system. Here we demonstrate that quantum nonlinear spectroscopy, in which a quantum sensor and a quantum object are first entangled and the sensor is measured along a chosen basis, can extract arbitrary types and orders of correlations in a quantum system. We measured fourth-order correlations of single nuclear spins that cannot be measured in conventional nonlinear spectroscopy, using sequential weak measurement via a nitrogen-vacancy center in diamond. The quantum nonlinear spectroscopy provides fingerprint features to identify different types of objects, such as Gaussian noises, random-phased AC fields, and quantum spins, which would be indistinguishable in second-order correlations. This work constitutes an initial step toward the application of higher-order correlations to quantum sensing, to examining the quantum foundation (by, e.g., higher-order Leggett-Garg inequality), and to studying quantum many-body physics.
传统的非线性光谱学使用经典探针，只能获取量子系统中有限的一组关联。在此，我们证明了量子非线性光谱学，即首先将量子传感器和量子对象纠缠，然后沿选定基测量传感器，可以提取量子系统中任意类型和阶次的关联。我们利用金刚石中的氮空位中心通过序列弱测量，测量了传统非线性光谱学无法测量的单核自旋的四阶关联。量子非线性光谱学提供了指纹特征，以识别不同类型的对象，如高斯噪声、随机相位交流场和量子自旋，这些在二阶关联中是无法区分的。这项工作是迈向将高阶关联应用于量子传感、检验量子基础（例如通过高阶莱格特 - 加尔格不等式）以及研究量子多体物理的第一步。
