Optomechanical Magnetometry with a Macroscopic Resonator

Whispering galley mode resonators have many applications, including photonic circuitry, optical clocks, and sensing. They can be used as magnetometers that operate in ambient conditions and require no cryogenics, but so far they have been limited to sensitivities above 100 nT in the crucial 1--1000 Hz frequency range. The authors engineer a combination of optical and mechanical resonances in such a system to detect kHz magnetic fields with sensitivity around 100 pT. This advance of three orders of magnitude opens the door to applications in geological surveying, medical imaging, and other areas.