Single nitrogen-vacancy (NV) centers are widely used as nanoscale sensors for magnetic and electric fields, strain and temperature. Nanoscale magnetometry using NV centers allows for example to quantitatively measure local magnetic fields produced by vortices in superconductors, topological spin textures such as skyrmions, as well as to detect nuclear magnetic resonance signals. However, one drawback when used as magnetic field sensor has been that an external bias field is required to perform magnetometry with NV centers. In this work we demonstrate a technique which allows access to a regime where no external bias field is needed. This enables new applications in which this bias field might disturb the system under investigation. Furthermore, we show that our technique is sensitive enough to detect spins outside of the diamond which enables nanoscale zero-to ultralow-field nuclear magnetic resonance.

单氮空位 (NV) 中心被广泛用作磁场和电场、应变和温度的纳米级传感器。例如，使用 NV 中心的纳米级磁力测量允许定量测量由超导体中的涡流产生的局部磁场、拓扑自旋纹理（如斯格明子），以及检测核磁共振信号。然而，当用作磁场传感器时，一个缺点是需要外部偏置场来执行具有 NV 中心的磁力测量。在这项工作中，我们展示了一种技术，该技术允许访问不需要外部偏置场的区域。这使得这种偏置场可能会干扰正在研究的系统的新应用成为可能。此外，