# Cavity cooling of a levitated nanosphere by coherent scattering

## TL;DR

This paper demonstrates three-dimensional cavity cooling of a levitated nanoparticle via coherent scattering, achieving significant cooling rates and noise suppression, paving the way for quantum ground state cooling at ultra-low pressures.

## Contribution

It introduces a novel cavity cooling method using coherent scattering for levitated nanoparticles, with experimental validation of enhanced cooling and noise suppression.

## Key findings

- Achieved 3D cooling of a nanoparticle inside an optical cavity.
- Demonstrated two orders of magnitude axial cooling at 6×10⁻² mbar.
- Estimated potential for quantum ground state cooling below 10⁻⁷ mbar.

## Abstract

We report three-dimensional cooling of a levitated nanoparticle inside an optical cavity. The cooling mechanism is provided by cavity-enhanced coherent scattering off an optical tweezer. The observed 3D dynamics and cooling rates are as theoretically expected from the presence of both linear and quadratic terms in the interaction between the particle motion and the cavity field. By achieving nanometer-level control over the particle location we optimize the position-dependent coupling and demonstrate axial cooling by two orders of magnitude at background pressures as high as $6\times10^{-2}$ mbar. We also estimate a significant ($> 40$ dB) suppression of laser phase noise, and hence of residual heating, which is a specific feature of the coherent scattering scheme. The observed performance implies that quantum ground state cavity cooling of levitated nanoparticles can be achieved for background pressures below $10^{-7}$ mbar.