Fast Coherent Control of a Nitrogen-Vacancy-Center Spin Ensemble Using a KTaO3 Dielectric Resonator at Cryogenic Temperatures

Abstract

Microwave delivery to samples in a cryogenic environment can pose experimental challenges such as restricting optical access, space constraints, and heat generation. Moreover, existing solutions that overcome various experimental restrictions do not necessarily provide a large homogeneous oscillating magnetic field over macroscopic length scales, which is required for control of spin ensembles or fast gate operations in scaled-up quantum computing implementations. Here, we show fast and coherent control of a negatively charged nitrogen-vacancy spin ensemble by taking advantage of the high permittivity of a ${\mathrm{K}\mathrm{Ta}\mathrm{O}}_{3}$ dielectric resonator at cryogenic temperatures. We achieve Rabi frequencies of up to 48 MHz, with a total power-to-field conversion factor ${C}_{\mathrm{P}}=\phantom{\rule{0.2em}{0ex}}9.66\phantom{\rule{0.2em}{0ex}}\mathrm{mT}/\sqrt{\mathrm{W}}$ (approximately $191\phantom{\rule{0.2em}{0ex}}{\mathrm{MHz}}_{\mathrm{Rabi}}/\sqrt{\mathrm{W}}$). We use the nitrogen-vacancy-center spin ensemble to probe the quality factor, the coherent enhancement, and the spatial distribution of the magnetic field inside the diamond sample. The key advantages of the dielectric resonator utilized in this work are ease of assembly, in situ tunability, a high magnetic field conversion efficiency, a low-volume footprint, and optical transparency. This makes ${\mathrm{K}\mathrm{Ta}\mathrm{O}}_{3}$ dielectric resonators a promising platform for the delivery of microwave fields for the control of spins in various materials at cryogenic temperatures.