Observation of radiation torque shot noise on an optically levitated nanodumbbell

TL;DR

This paper reports the experimental observation of radiation torque shot noise affecting the angular orientation of an optically levitated nanodumbbell, demonstrating quantum measurement backaction in rotational degrees of freedom.

Contribution

It provides the first direct observation of radiation torque shot noise on a levitated nanodumbbell, linking quantum measurement backaction to rotational motion.

Findings

Radiation torque shot noise dominates reheating in high vacuum.

Feedback cooling reduces rotational motion, enabling observation of shot noise.

Reheating behavior confirms quantum backaction effects on rotation.

Abstract

According to quantum theory, measurement and backaction are inextricably linked. In optical position measurements, this backaction is known as radiation pressure shot noise. In analogy, a measurement of the orientation of a mechanical rotor must disturb its angular momentum by radiation torque shot noise. In this work, we observe the shot-noise torque fluctuations arising in a measurement of the angular orientation of an optically levitated nanodumbbell. We feedback cool the dumbbell's rotational motion and investigate its reheating behavior when released from feedback. In high vacuum, the heating rate due to radiation torque shot noise dominates over the thermal and technical heating rates in the system.