Vector detection of ac magnetic fields by nitrogen vacancy centers of single orientation in diamond

Nitrogen vacancy (NV) centers in diamond have useful properties for detecting both ac and dc magnetic fields with high sensitivity at nanoscale resolution. The vector detection of ac magnetic fields can be achieved by using NV centers having three different orientations. Here, we propose a method to achieve this by using NV centers of single orientation. In this method, a static magnetic field is applied perpendicular to the NV axis, leading to strong mixing of the ms=-1 and 1 electron spin states. As a result, all three electron spin transitions of the triplet ground state have nonzero dipole moments, with each transition coupling to a single component of the magnetic field. This can be used to measure both the strength and orientation of the applied ac field. To validate the technique, we perform a proof-of-principle experiment using a subset of ensemble NV centers in diamond, all having the same orientation. This method is equally applicable to single NV centers.