Near-field GHz rotation and sensing with an optically levitated nanodumbbell

TL;DR

This paper demonstrates GHz rotation of an optically levitated nanodumbbell near a surface, achieving high torque sensitivity and enabling near-field sensing beyond diffraction limits, with implications for probing fundamental quantum interactions.

Contribution

It introduces a method to levitate and rotate a nanodumbbell at GHz frequencies near surfaces, enabling sensitive torque measurements and near-field sensing beyond diffraction limits.

Findings

Achieved nanodumbbell rotation at 430 nm from a surface at GHz frequencies.

Measured torque sensitivity of approximately 5 x 10^{-26} Nm/Hz^{1/2} at room temperature.

Showed potential for detecting Casimir torque using the levitated nanodumbbell.

Abstract

A levitated non-spherical nanoparticle in a vacuum is ideal for studying quantum rotations and is an extremely sensitive torque and force detector. It has been proposed to probe fundamental particle-surface interactions such as the Casimir torque and the rotational quantum vacuum friction, which require it to be driven to rotate near a surface at sub-micrometer separations. Here, we optically levitate a silica nanodumbbell in a vacuum at about 430 nm away from a sapphire surface and drive it to rotate at GHz frequencies. The relative linear speed between the tip of the nanodumbbell and the surface reaches 1.4 km/s at a sub-micrometer separation. The rotating nanodumbbell near the surface demonstrates a torque sensitivity of $(5.0 \pm 1.1) \times 10^{-26} {\rm NmHz}^{-1/2}$ at room temperature. Moreover, we levitate a nanodumbbell near a gold nanograting and use it to probe the near-field intensity distribution beyond the optical diffraction limit. Our numerical simulation shows it is promising to detect the Casimir torque between a nanodumbbell and a nanograting.