Ultrabroadband and sensitive cavity optomechanical magnetometry
Bei‐Bei Li, George A. Brawley, Hamish Greenall, Stefan Forstner, Eoin Sheridan, Halina Rubinsztein‐Dunlop, Warwick P. Bowen
Abstract
Magnetostrictive optomechanical cavities provide a new optical readout approach to room-temperature magnetometry. Here we report ultrasensitive and ultrahigh bandwidth cavity optomechanical magnetometers constructed by embedding a grain of the magnetostrictive material Terfenol-D within a high quality ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:mi>Q</mml:mi> </mml:mrow> </mml:math> ) optical microcavity on a silicon chip. By engineering their physical structure, we achieve a peak sensitivity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m2"> <mml:mrow> <mml:mn>26</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>pT</mml:mi> <mml:mo>/</mml:mo> <mml:msqrt> <mml:mi>Hz</mml:mi> </mml:msqrt> </mml:mrow> </mml:math> comparable to the best cryogenic microscale magnetometers, along with a 3 dB bandwidth as high as 11.3 MHz. Two classes of magnetic response are observed, which we postulate arise from the crystallinity of the Terfenol-D. This allows single crystalline and polycrystalline grains to be distinguished at the level of a single particle. Our results may enable applications such as lab-on-chip nuclear magnetic spectroscopy and magnetic navigation.