Broadband loop gap resonator for nitrogen vacancy centers in diamond

We present an S-band tunable loop gap resonator (LGR), which provides strong, homogeneous, and directionally uniform broadband microwave (MW) drive for nitrogen-vacancy (NV) ensembles. With 42 dBm of input power, the composite device provides drive field amplitudes approaching 5 G over a circular area greater than or similar to 50 mm (2) or cylindrical volume greater than or similar to 250 mm(3). The wide 80 MHz device bandwidth allows driving all NV Zeeman resonances for bias magnetic fields below 20 G. The device realizes percent-scale MW drive inhomogeneity; we measure a fractional root-mean-square inhomogeneity sigma(rms) = 1.6% and a peak-to-peak variation sigma(pp) = 3% over a circular area of 11 mm(2) and sigma(rms) = 3.2% and sigma(pp) = 10.5% over a larger 32 mm(2) circular area. We demonstrate incident MW power coupling to the LGR using two methodologies: a printed circuit board-fabricated exciter antenna for deployed compact bulk sensors and an inductive coupling coil suitable for microscope-style imaging. The inductive coupling coil allows for approximately 2 pi steradian combined optical access above and below the device, ideal for envisioned and existing NV imaging and bulk sensing applications. Published by AIP Publishing.