Microwave-Free Magnetometry Based On Cross-Relaxation Resonances In Diamond Nitrogen-Vacancy Centers

We study cross-relaxation resonances between differently oriented groups of nitrogen-vacancy (NV) centers at small external magnetic fields. These resonances are observed using resonant optical pumping on the NV-center zero phonon line. We suggest a magnetometry protocol that is based on measuring the positions of cross-relaxation resonances on the fluorescence scan. This protocol does not require microwave radiation and can be used to find all components of the unknown magnetic field vector. A room-temperature variant of the protocol with off-resonant optical pumping is also briefly discussed.