Multiplexed sensing of magnetic field and temperature in real time using a nitrogen vacancy spin ensemble in diamond.

Nitrogen-Vacancy (NV) spin in diamond is a versatile quantum sensor, being able to measure physical quantities such as magnetic field, electric field, temperature, and pressure. However, sensing more than a single quantity simultaneously has not been realized previously. In the present work, we demonstrate a multiplexed sensing of magnetic field and temperature. Unlike time-division, the dual frequency driving technique we employ here is based on frequency-division multiplexing, which enables sensing both measurables in real time. The pair of NV resonance frequencies for dual frequency driving must be selected to avoid coherent population trapping of NV spin states. With an enhanced optical collection efficiency higher than 50 % and a type 1b diamond crystal with natural abundance $^{13}$C spins, we achieve sensitivities of about 70 pT/Hz$^{1/2}$ and 25 $\mu$K/Hz$^{1/2}$ simultaneously with an isolation factor of about 34 dB. This work paves the way for extending the application of NV quantum diamond sensors into more demanding conditions.