Ultrasensitive Optomechanical Magnetometry

摘要

Whispering gallery mode (WGM) microresonators are a powerful tool for applications including lasing, optical switching, non-linear optics, and in particular, sensing. Due to their strong optical confinement and small mode volumes, such devices provide an excellent platform for strong light-matter interactions allowing, for instance, the detection of single proteins and viruses, as well as applications in cavity quantum electrodynamics and quantum computing. Furthermore, the combination of mechanical and optical resonances accessible in optomechanical WGMs such as silica microtoroids provides enhanced mechanical response to applied forces and optical readout with attometer precision. This has enabled rapid advances in the field of quantum optomechanics, including the demonstration of quantum-coherent coupling, optomechani-cally induced transparency, and optomechanical cooling. Furthermore, cavity optomechanical devices have led to the realization of state-of-the-art sensitivities in force sensing and accelerometry. Here, we report an optomechanical magnetometer operating for the first time in the 100 pT range, an advance of more than three orders of magnitude on the sole previously reported cavity optomechanical magnetometer. When compared with electronic magnetometers, optical magnetometers offer the intrinsic advantage of low electromagnetic interference and further, evade electronic measurement noise, which constrains the sensitivity and bandwidth of electronic magnetometers. In comparably sized electronic magnetostrictive magnetometers, electronic noise limits the sensitivity to values three-orders-of-magnitude inferior to the sensitivity reported here. The device operates at earth field, is fiber coupled, silicon-chip based, and achieves tens of megahertz bandwidth. Furthermore, non-linearities in the response of the magnetometer allow its functionality to be extended to frequencies as low as 2 Hz, though with reduced sensitivity of 150 nT Hz~(-1/2). Combined with 60 μm spatial resolution and microwatt power requirements, these unique capabilities offer the prospect for a range of potential applications including cryogen-free and microfluidic magnetic resonance imaging (MRI), and investigation of spin physics in condensed matter systems such as semiconductors and ultracold atom clouds.