Design and simulation of a strong and uniform microwave antenna for a large volume of nitrogen-vacancy ensembles in diamond

We present a three-dimensional microwave antenna design, which can provide strong and spatially homogeneous GHz microwaves for efficient driving of nitrogen-vacancy (NV) ensembles in a diamond. From numerical simulation, we find the field strength to be as large as ~ 21 G at 2.87 GHz equivalent to an ~ 60 MHz Rabi frequency. In addition, the field remains uniform over an ~ mm³ volume of the diamond. We determine the antenna parameters and configurations based on quantitative analyses of the simulation results in terms of the loop radius, the number of coil, the dielectric materials and the coil configurations of the solenoid and Helmholtz coil. The antenna design studied in this research can be used in various sensing applications based on the NV ensemble, where a strong and uniform microwave drive is necessary.