Level anti-crossings of a nitrogen-vacancy center in diamond: decoherence-free subspaces and 3D sensors of microwave magnetic fields

Abstract

Nitrogen-vacancy (NV) centers in diamond have become an important tool for quantumtechnologies. All of these applications rely on long coherence times of electron and nuclear spinsassociated with these centers. Here, we study the energy level anti-crossings of an NV center indiamond coupled to a first-shell13C nuclear spin in a small static magnetic field. These levelanti-crossings (LACs) occur for specific orientations of the static magnetic field due to the strongnon-secular components of the Hamiltonian. At these orientations we observe decoherence-freesubspaces, where the electron spin coherence times (T∗2) are 5–7 times longer than those at otherorientations. Another interesting property at these LACs is that individual transition amplitudesare dominated by a single component of the magnetic dipole moment. Accordingly, this can beused for vector detection of microwave magnetic fields with a single NV center. This is particularlyimportant to precisely control the center using numerical optimal control techniques.