Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique for analysing the structure and function of molecules, and for performing three-dimensional imaging of their spin densities. At the heart of NMR spectrometers is the detection of electromagnetic radiation, in the form of a free induction decay signal1, generated by nuclei precessing around an applied magnetic field. Whereas conventional NMR requires signals from 1012 or more nuclei, recent advances in sensitive magnetometry2,3 have dramatically lowered the required number of nuclei to a level where a few or even individual nuclear spins can be detected4–6. It is unclear whether continuous detection of the free induction decay can still be applied at the single-spin level, or whether quantum back-action (the effect that a detector has on the measurement itself) modifies or suppresses the NMR response. Here we report the tracking of single nuclear spin precession using periodic weak measurements7–9. Our experimental system consists of nuclear spins in diamond that are weakly interacting with the electronic spin of a nearby nitrogen vacancy centre, acting as an optically readable meter qubit. We observe and minimize two important effects of quantum back-action: measurement-induced decoherence10 and frequency synchronization with the sampling clock11,12. We use periodic weak measurements to demonstrate sensitive, high-resolution NMR spectroscopy of multiple nuclear spins with a priori unknown frequencies. Our method may provide a useful route to single-molecule NMR13,14 at atomic resolution.Periodic weak measurements of just a few carbon-13 nuclear spins in diamond demonstrate sensitive, high-resolution nuclear magnetic resonance spectroscopy at the molecular level.

中文翻译：

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通过弱测量跟踪单核自旋的进动

核磁共振 (NMR) 光谱是分析分子结构和功能以及对其自旋密度进行三维成像的强大技术。核磁共振波谱仪的核心是检测电磁辐射，以自由感应衰变信号 1 的形式，由原子核围绕外加磁场进动产生。传统 NMR 需要来自 1012 个或更多原子核的信号，而敏感磁力测定法的最新进展 2,3 已将所需原子核数量显着降低到可以检测到几个甚至单个核自旋的水平 4-6。目前尚不清楚自由感应衰减的连续检测是否仍然适用于单自旋水平，或者量子反作用（探测器对测量本身的影响）是否会修改或抑制 NMR 响应。在这里，我们报告使用周期性弱测量 7-9 跟踪单核自旋进动。我们的实验系统由金刚石中的核自旋组成，这些核自旋与附近氮空位中心的电子自旋微弱相互作用，充当光学可读的仪表量子位。我们观察并最小化量子反作用的两个重要影响：测量引起的退相干 10 和与采样时钟的频率同步 11,12。我们使用周期性弱测量来展示具有先验未知频率的多个核自旋的灵敏、高分辨率 NMR 光谱。我们的方法可能为原子分辨率的单分子 NMR13,14 提供有用的途径。