Probing the nitrogen vacancy center using the Faraday effect at room temperature

The spin states of the nitrogen vacancy ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msup> <a:mrow> <a:mi>NV</a:mi> </a:mrow> <a:mo>−</a:mo> </a:msup> </a:math> ) center in diamond are used in, among others, quantum computing, nanoscale imaging, and magnetic field sensing, and have been proposed for fundamental physics experiments. The states of <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:msup> <b:mrow> <b:mi>NV</b:mi> </b:mrow> <b:mo>−</b:mo> </b:msup> </b:math> centers are traditionally measured using the spin-state-dependent photoluminescence—a destructive and often inefficient measurement scheme. In this article, using a single laser beam as a pump and a probe, we measure the spin states of the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:msup> <c:mrow> <c:mi>NV</c:mi> </c:mrow> <c:mo>−</c:mo> </c:msup> </c:math> centers nondestructively using the Faraday effect at room temperature. Using the optical selection rules and the helicity-dependent absorption, we identify the optical transitions of the <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:msup> <d:mrow> <d:mi>NV</d:mi> </d:mrow> <d:mo>−</d:mo> </d:msup> </d:math> center responsible for the Faraday effect and confirm the existence of spin-orbit coupling in such centers at room temperature. Our results indicate that experiments such as NV spin-photon entanglement and electromagnetically induced transparency are viable in ambient conditions. Finally, using the Faraday effect, we develop a magnetic field sensor and argue that, with the inclusion of an optical cavity, a femtotesla-level magnetic field sensitivity can be achieved.