Thermally Polarized Solid-State Spin Sensor

Quantum sensors based on spin defect ensembles have seen rapid development in recent years, with a wide array of target applications. Historically, these sensors have used optical methods to prepare or read out quantum states. However, these methods are limited to optically polarizable spin defects, and the spin ensemble size is typically limited by the available optical power or acceptable optical heat load. We demonstrate a solid-state sensor employing a nonoptical state preparation technique, which harnesses thermal population imbalances induced by the defects' zero-field splitting. Readout is performed using the recently demonstrated microwave cavity readout technique, resulting in a sensor architecture that is entirely nonoptical and broadly applicable to all solid-state paramagnetic defects with a zero-field splitting. The implementation in this work uses Cr3+ defects in a sapphire (Al2O3) crystal and a simple microwave architecture where the host crystal also serves as the high quality-factor resonator. This approach yields a near-unity filling factor and high single-spin-photon coupling, producing a broadband magnetometer with a minimum sensitivity of 9.7 pT root Hz near 5 kHz.

Automated summary

Quantum sensors based on spin defect ensembles have achieved rapid development by utilizing a nonoptical state preparation technique and microwave cavity readout technique, resulting in a nonoptical sensor architecture that is applicable to all solid-state paramagnetic defects with a zero-field splitting.