Nitrogen vacancy center in diamond-based Faraday magnetometer

The nitrogen vacancy (NV) center in diamond is a versatile color center used for magnetometry, quantum computing, and quantum communications. In this article, using a single laser beam as a pump and probe, we measure the spin states of the NV center using the Faraday effect and use such measurements to develop a novel magnetic field sensor. Using the spin-state-dependent effect on the left and right circularly polarized light, we probe and confirm the existence of spin-orbit coupling in the NV center at room temperature. The sensitivity of our magnetometer is $350$nT/$\sqrt{Hz}$, limited by the background produced by the laser trapped inside the diamond. We argue that by using an optical cavity and a high-purity diamond, sensitivities in the femtotesla level can be achieved.