Multiplexed Sensing of Magnetic Field and Temperature in Real Time Using a Nitrogen-Vacancy Ensemble in Diamond

Abstract

The nitrogen-vacancy ($\mathrm{N}$-$V$) defect in diamond is a versatile quantum sensor, being able to measure physical quantities such as magnetic field, electric field, temperature, and pressure. In the present work, we demonstrate multiplexed sensing of magnetic field and temperature using a N-V ensemble in diamond. The dual-frequency-driving technique we employ is based on frequency-division multiplexing, which enables the sensing of both measurables in real time. The pair of $\mathrm{N}$-$V$ resonance frequencies for dual-frequency driving must be selected to avoid coherent population trapping of $\mathrm{N}$-$V$ spin states. With enhanced optical collection efficiency higher than 50% and a type 1b diamond crystal with a natural abundance of ${}^{13}\mathrm{C}$ spins, we achieve sensitivities of about $70\phantom{\rule{0.2em}{0ex}}\mathrm{pT}/\sqrt{\mathrm{Hz}}$ and $25\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{K}/\sqrt{\mathrm{Hz}}$ simultaneously. We demonstrate a high isolation factor of 34 dB in the $\mathrm{N}$-$V$ thermometry signal against the magnetic field; and we provide a theoretical description for the isolation factor. This work paves the way for extending the application of $\mathrm{N}$-$V$ diamond sensors into more demanding conditions.