Cooling of an optically levitated nanoparticle via measurement-free coherent feedback

TL;DR

This paper demonstrates a measurement-free optical feedback method to cool a levitated nanoparticle, achieving low phonon occupations and offering a tunable, correlation-preserving control technique for quantum systems.

Contribution

It introduces a novel all-optical coherent feedback scheme for nanoparticle cooling, surpassing measurement-based methods and analyzing phase noise limitations.

Findings

Achieved phonon occupations down to a few hundred.

Demonstrated tunable control via feedback phase and delay.

Identified phase noise as a key limitation to ground-state cooling.

Abstract

We demonstrate coherent, measurement-free optical feedback control of a levitated nanoparticle, achieving phonon occupations down to a few hundred phonons. Unlike measurement-based feedback, this all-optical scheme preserves the correlations between mechanical motion and the feedback signal. Adjustment of the feedback phase and delay provides precise and tunable control over the system dynamics. The ultimate cooling performance is currently limited by phase noise, which we analyze within a theoretical framework that outlines the constraints and prospects for reaching the motional ground state. Our results establish coherent feedback as a powerful tool for quantum control of levitated systems, extending beyond center-of-mass cooling.