Demonstration of highly-sensitive wideband microwave sensing using ensemble nitrogen-vacancy centers

Microwave magnetometry is essential for the advancement of microwave technologies. We demonstrate a broadband microwave sensing protocol using the AC Zeeman effect with ensemble nitrogen-vacancy (NV) centers in diamond. A widefield microscope can visualize the frequency characteristics of the microwave resonator and the spatial distribution of off-resonant microwave amplitude. Furthermore, by combining this method with dynamical decoupling, we achieve the microwave amplitude sensitivity of $5.2\mu \mathrm{T}\mathrm{/}\sqrt{\mathrm{H}\mathrm{z}}$, which is 7.7 times better than $40.2\mu \mathrm{T}\mathrm{/}\sqrt{\mathrm{H}\mathrm{z}}$ obtained using the protocol in previous research over a sensing volume of $2.77\mu \mathrm{m}\times 2.77\mu \mathrm{m}\times 30\mathrm{n}\mathrm{m}$. Our achievement is a concrete step in adapting ensemble NV centers for wideband and widefield microwave imaging.