Laser-enhanced quantum sensing boosts sensitivity and dynamic range
Magnetometers based on nitrogen-vacancy (NV) centers in diamond have emerged as the most important solid-state quantum sensors. However, ensembles are limited in optical contrast to typically a few percent and high-sensitivity variants usually possess only a few $\mathrm{\upmu}$T dynamic range. Here, we demonstrate a laser threshold magnetometry-based NV system that avoids these limitations. By integrating the NV centers into a laser cavity and showing magnetic-field-dependent shifts of the laser threshold, we observe 100\,\% optical contrast, i.\,e., we are able to entirely switch off the laser system with the NV centers magnetic resonance. At the same time we achieve strong output signals up to 50\,mW. The system exhibits a photon-shot-noise-limited (PSNL) sensitivity of $<$400\,fT/$\sqrt{\textrm{Hz}}$ for all vector components, which we demonstrate to improve super-linearly with contrast. The ratio of the sensing-relevant parameters PSNL sensitivity and dynamic range, that can be traded at the cost of each other, marks an improvement factor of up to 590 over typical fluorescence-based readout and vapor cell sensors while also adding vector magnetometry capabilities. Such performance improvements provide a perspective for a highly sensitive magnetometer, which could be operated outside a magnetically-shielded room. This could bring a new generation of sensors for applications including magnetoencephalography, magnetic navigation, and magnetic anomaly detection.