Ultrasensitive cavity optomechanical magnetometry

Ultra-low field magnetic field sensors are essential for many applications including geology, mineral exploration, archaeology and medicine [1]. However, such magnetometers typically either require cryogenic systems to operate, or suffer poor dynamic range, limiting their ability to operate in ambient conditions. Here, we demonstrate a microscale room temperature cavity optomechanical magnetometer operating in the picoTelsa sensitivity range (see Fig. 1a). The peak sensitivity of 200 pT Hz^-1/2 exceeds that of any previous room temperature magnetometer of its size, and is a factor of 2,000 better than the only previously reported cavity optomechanical magnetometer [2]. Furthermore, we demonstrate that an inherent paramagnetic nonlinearity allows mix-up of low frequency to the RF frequency band, enabling magnetic field sensing in the Hz-kHz frequency window crucial for applications such as medical imaging, geosurvey, and magnetic anomaly detection (see Fig. 1b). This presents an enabling step towards real applications of cavity optomechanical magnetometers in high-performance microscale magnetometry.