Thermal nonlinearities in a nanomechanical oscillator

TL;DR

This paper investigates thermal nonlinearities in optically trapped nanoparticles, demonstrating how thermal energy induces nonlinear motion, characterizing frequency fluctuations, and using feedback cooling to enhance force sensing sensitivity to 20 zN/Hz^{1/2}.

Contribution

It provides the first experimental characterization of thermal nonlinearities in levitated nanoparticles and shows how feedback cooling improves force sensitivity at room temperature.

Findings

Thermal energy drives nanoparticles into nonlinear motion.

Frequency fluctuations from thermal motion are fully characterized.

Feedback cooling reduces fluctuations and enhances force sensitivity.

Abstract

Nano- and micromechanical oscillators with high quality (Q) factors have gained much attention for their potential application as ultrasensitive detectors. In contrast to micro-fabricated devices, optically trapped nanoparticles in vacuum do not suffer from clamping losses, hence leading to much larger Q-factors. We find that for a levitated nanoparticle the thermal energy suffices to drive the motion of the nanoparticle into the nonlinear regime. First, we experimentally measure and fully characterize the frequency fluctuations originating from thermal motion and nonlinearities. Second, we demonstrate that feedback cooling can be used to mitigate these fluctuations. The high level of control allows us to fully exploit the force sensing capabilities of the nanoresonator. Our approach offers a force sensitivity of 20 zN $Hz^{-1/2}$, which is the highest value reported to date at room temperature, sufficient to sense ultra-weak interactions, such as non-Newtonian gravity-like forces.