The detection of faint magnetic fields from single-electron and nuclear spins at the atomic scale is a long-standing challenge in physics. While current mobile quantum sensors achieve single-electron spin sensitivity, atomic spatial resolution remains elusive for existing techniques. Here we fabricate a single-molecule quantum sensor at the apex of the metallic tip of a scanning tunnelling microscope by attaching Fe atoms and a PTCDA (3,4,9,10-perylenetetracarboxylic-dianhydride) molecule to the tip apex. We address the molecular spin by electron spin resonance and achieve ~100 neV resolution in energy. In a proof-of-principle experiment, we measure the magnetic and electric dipole fields emanating from a single Fe atom and an Ag dimer on an Ag(111) surface with sub-angstrom spatial resolution. Our method enables atomic-scale quantum sensing experiments of electric and magnetic fields on conducting surfaces and may find applications in the sensing of spin-labelled biomolecules and of spin textures in quantum materials.

在原子尺度上检测来自单电子和核自旋的微弱磁场是物理学中一个长期的挑战。虽然目前的移动量子传感器实现了单电子自旋灵敏度，但原子空间分辨率对于现有技术来说仍然难以捉摸。在这里，我们通过将 Fe 原子和 PTCDA（3,4,9,10-苝四羧酸二酐）分子连接到尖端，在扫描隧道显微镜的金属尖端的顶点制造了一个单分子量子传感器。我们通过电子自旋共振解决分子自旋问题，并在能量中实现 ~100 neV 分辨率。在原理验证实验中，我们以亚埃空间分辨率测量了 Ag（111） 表面上的单个 Fe 原子和 Ag 二聚体发出的磁偶极子场和电偶极子场。我们的方法能够对导电表面上的电场和磁场进行原子级量子传感实验，并可能在自旋标记的生物分子和量子材料中自旋纹理的传感中找到应用。