Multiphoton resonances in nitrogen-vacancy defects in diamond

Dense ensembles of nitrogen-vacancy (NV) centers in diamond are of interest for various applications, including magnetometry, masers, hyperpolarization, and quantum memory. All of the applications above may benefit from a nonlinear response of the ensemble, and hence multiphoton processes are important. An enhancement of the multiphoton response is demonstrated by coupling the NV ensemble to a superconducting cavity. Moreover, the measured multiphoton response of the NV ensemble exhibits a regular pattern, which suggests that a dipolar coupling to nitrogen-14 substitutional defects (P1) plays a role in this process. As an example of an application, increased responsivity to magnetic field is demonstrated.