Inert shell coating for enhanced laser refrigeration of nanoparticles: application in levitated optomechanics

TL;DR

This study demonstrates that inert shell coatings on lanthanide-doped nanocrystals significantly improve laser refrigeration efficiency, enabling cooling down to 147 K in levitated optomechanical systems.

Contribution

We designed and tested core-shell nanoparticles with inert coatings, showing enhanced cooling performance over bare nanocrystals for levitated optomechanics.

Findings

Core-shell nanoparticles cooled to 147 K at 26 mbar.

Significant cooling observed in core-shell compared to bare nanoparticles.

Core-shell design improves minimum final temperature in laser refrigeration.

Abstract

We report on a study exploring the design of nanoparticles that can enhance their laser refrigeration efficiency for applications in levitated optomechanics. In particular, we developed lanthanide-doped nanocrystals with an inert shell coating and compared their performance with bare nanocrystals. While optically levitated, we studied the refrigeration of both types of nanoparticles while varying the pressure. We found that the core-shell design shows an improvement in the minimum final temperature: a fourth of the core-shell nanoparticles showed a significant cooling compared to almost none of the bare nanoparticles. Furthermore, we measured a core-shell nanoparticle cooling down to a temperature of 147 K at 26 mbar in the underdamped regime. Our study is a first step towards engineering nanoparticles that are suitable for achieving absolute (centre-of-mass and internal temperature) cooling in levitation, opening new avenues for force sensing and the realization of macroscopic quantum superpositions.