A cavity optomechanical magnetometer is demonstrated. The magnetic-field-induced expansion of a magnetostrictive material is resonantly transduced onto the physical structure of a highly compliant optical microresonator and read out optically with ultrahigh sensitivity. A peak magnetic field sensitivity of $400\mathrm{nT}{\mathrm{Hz}}^{-1/2}$ is achieved, with theoretical modeling predicting the possibility of sensitivities below $1\mathrm{pT}{\mathrm{Hz}}^{-1/2}$. This chip-based magnetometer combines high sensitivity and large dynamic range with small size and room temperature operation.

• Received 10 October 2011

DOI:https://doi.org/10.1103/PhysRevLett.108.120801