Broadband, large-area microwave antenna for optically-detected magnetic   resonance of nitrogen-vacancy centers in diamond
  We report on a microwave planar ring antenna specifically designed for optically-detected magnetic resonance (ODMR) of nitrogen-vacancy (NV) centers in diamond. It has the resonance frequency at around 2.87 GHz with the bandwidth of 400 MHz, ensuring that ODMR can be observed under external magnetic fields up to 100 G without the need of adjustment of the resonance frequency. It is also spatially uniform within the 1-mm-diameter center hole, enabling the magnetic-field imaging in the wide spatial range. These features facilitate the experiments on quantum sensing and imaging using NV centers at room temperature. 
Kento Sasaki, Yasuaki Monnai, Soya Saijo, Ryushiro Fujita, Hideyuki   Watanabe, Junko Ishi-Hayase, Kohei M. Itoh, Eisuke Abe
cond-mat.mes-hall