Magnetic Actuation and Feedback Cooling of a Cavity Optomechanical Torque Sensor

TL;DR

This paper presents a cavity optomechanical system integrating a ferromagnetic needle for sensitive magnetic measurements, amplification, and cooling of mechanical motion, enabling nanomagnetic studies and enhanced torque sensing.

Contribution

It introduces a novel integration of a ferromagnetic needle with a cavity optomechanical resonator for magnetic property measurement and motion control.

Findings

Measured torques as small as 32 zNm.

Extracted magnetization of 1710 kA/m.

Damped mechanical mode temperature from room temperature to 11.6 K.

Abstract

We demonstrate the integration of a mesoscopic ferromagnetic needle with a cavity optomechanical torsional resonator, and its use for quantitative determination of the needle's magnetic properties, as well as amplification and cooling of the resonator motion. With this system we measure torques as small as 32 zNm, corresponding to sensing an external magnetic field of 0.12 A/m (150 nT). Furthermore, we are able to extract the magnetization (1710 kA/m) of the magnetic sample, not known a priori, demonstrating this system's potential for studies of nanomagnetism. Finally, we show that we can magnetically drive the torsional resonator into regenerative oscillations, and dampen its mechanical mode temperature from room temperature to 11.6 K, without sacrificing torque sensitivity.