Level anti-crossings of an NV center in diamond: Decoherence-free subspaces and 3D sensors of microwave magnetic fields

TL;DR

This paper investigates energy level anti-crossings in NV centers in diamond, revealing decoherence-free subspaces that enhance coherence times and enabling vector detection of microwave magnetic fields for quantum sensing applications.

Contribution

It demonstrates the existence of decoherence-free subspaces at specific magnetic field orientations and shows their potential for improved quantum sensing and control.

Findings

Electron spin coherence times are 5-7 times longer at anti-crossings.

Individual transition amplitudes are dominated by a single magnetic dipole component.

Anti-crossings enable vector detection of microwave magnetic fields.

Abstract

Nitrogen-vacancy (NV) centers in diamond have become an important tool for quantum technologies. All of these applications rely on long coherence times of electron and nuclear spins associated with these centers. Here, we study the energy level anti-crossings of an NV center in diamond coupled to a first-shell 13C nuclear spin in a small static magnetic field. These level anti-crossings occur for specific orientations of the static magnetic field due to the strong non-secular components of the Hamiltonian. At these orientations we observe decoherence-free subspaces, where the electron spin coherence times (T_2* ) are 5-7 times longer than those at other orientations. Another interesting property at these level anti-crossings is that individual transition amplitudes are dominated by a single component of the magnetic dipole moment. Accordingly, this can be used for vector detection of microwave magnetic fields with a single NV center. This is particularly important to precisely control the center using numerical optimal control techniques.