Magnetic sensing at zero field with a single nitrogen-vacancy center

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