# Electrically Driven, Optically Levitated Microscopic Rotors

## TL;DR

This paper demonstrates electrically driven rotation of optically levitated microspheres, providing enhanced control over their angular motion and enabling precise measurements of torque and microsphere properties.

## Contribution

It introduces a method for electrically controlling the rotation of optically levitated microspheres, surpassing purely optical techniques in control and measurement capabilities.

## Key findings

- Measured spin-down and harmonic motion of microspheres
- Observed gyroscopic precession consistent with equations of motion
- Achieved precise control of microsphere angular momentum

## Abstract

We report on the electrically driven rotation of $2.4~\mu$m-radius, optically levitated dielectric microspheres. Electric fields are used to apply torques to a microsphere's permanent electric dipole moment, while angular displacement is measured by detecting the change in polarization state of light transmitted through the microsphere (MS). This technique enables greater control than previously achieved with purely optical means because the direction and magnitude of the electric torque can be set arbitrarily. We measure the spin-down of a microsphere released from a rotating electric field, the harmonic motion of the dipole relative to the instantaneous direction of the field, and the phase lag between the driving electric field and the dipole moment of the MS due to drag from residual gas. We also observe the gyroscopic precession of the MS when the axis of rotation of the driving field and the angular momentum of the microsphere are orthogonal. These observations are in quantitative agreement with the equation of motion. The control offered by the electrical drive enables precise measurements of microsphere properties and torque as well as a method for addressing the direction of angular momentum for an optically levitated particle.