Optomechanical Magnetometry with a Macroscopic Resonator

We demonstrate a centimeter-scale optomechanical magnetometer based on a crystalline whispering-gallery-mode resonator. The large size of the resonator, with a magnetic-field integration volume of 0.45 cm3, allows high magnetic-field sensitivity to be achieved in the hertz-to-kilohertz frequency range. A peak sensitivity of 131 pT Hz-1/2 is reported, in a magnetically unshielded noncryogenic environment using optical power levels beneath 100 μW. Femtotesla-range sensitivity may be possible in future devices with the further optimization of laser noise and the physical structure of the resonator, allowing applications in high-performance magnetometry.