Broadband loop gap resonator for nitrogen vacancy centers in diamond

Abstract

We present an S-band tunable loop gap resonator (LGR) providing 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 $\gtrsim 50$ mm${}^2$ or cylindrical volume $\gtrsim 250$ mm${}^3$. The wide 80 MHz device bandwidth allows driving all eight NV Zeeman resonances for bias magnetic fields below 20 G. For pulsed applications the device realizes percent-scale microwave drive inhomogeneity; we measure a fractional root-mean-square inhomogeneity ${\sigma }_{\text{rms}}=1.6\%$ and a peak-to-peak variation ${\sigma }_{\text{pp}}=3\%$ over a circular area of 11 mm${}^2$, and ${\sigma }_{\text{rms}}=3.2\%$ and ${\sigma }_{\text{pp}}=10.5\%$ over a larger 32 mm${}^2$ circular area. We demonstrate incident MW power coupling to the LGR using multiple methodologies: a PCB-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.

8 pages, 8 figures