Assegid M. Flatae

A robust technique is introduced for vector magnetometry based on polarimetry and optically detected magnetic resonance of ensembles of negatively charged nitrogen‐vacancy (NV – ) centers in diamond without a magnetic bias field. Ensembles provide a far greater signal‐to‐noise ratio than single centers, and their creation requires less effort. Previous methods for vector magnetometry using ensembles of NV – centers relied on a calibrated magnetic bias field or on complex detection techniques to distinguish the crystal axes. Instead, this work uses out‐of‐plane polarized light to selectively excite NV – centers oriented along specific crystal axes. This approach is general for other spin‐1 color centers with symmetry, and it is compatible with standard microscopy methods, such as scanning probe, superresolution, confocal, and wide‐field imaging.