Millihertz magnetic resonance spectroscopy combining the heterodyne readout based on solid-spin sensors.

The sensitivities of quantum sensing in metrology and spectroscopy are drastically influenced by the resolution of the frequency spectrum. However, the resolution is hindered by the decoherence effect between the sensor and the environment. Along these lines, the continue-wave optically detected magnetic resonance (CWODMR) method combined with the heterodyne readout was proposed to break the limitation of the sensor's coherence time.

High-efficiency fluorescence collection for NV center ensembles in diamond.

The negatively charged nitrogen vacancy (NV) center ensembles in diamond have been demonstrated to be a promising platform for quantum metrology, but the poor fluorescence collection efficiency of a microscope objective limits the sensitivity of the NV based sensors. Here we present a method for increasing the collected fluorescence intensity with a total internal reflection (TIR) lens. The detected fluorescence intensity is increased by approximately a factor of 56 compared with detection using a microscope objective with NA = 0.