Recoil-limited feedback cooling of single nanoparticles near the ground state in an optical lattice

TL;DR

This study demonstrates near-ground-state feedback cooling of single nanoparticles in an optical lattice, highlighting the critical role of laser phase noise reduction in achieving ultra-cold motional states.

Contribution

It provides a direct link between laser phase noise and nanoparticle heating, establishing a model that predicts occupation number limits due to photon recoil heating.

Findings

Laser phase noise causes significant heating along the optical lattice.

Reducing laser phase noise lowers the occupation number to about three.

Photon recoil heating limits the lowest achievable occupation number.

Abstract

We report on direct feedback cooling of single nanoparticles in an optical lattice to near their motional ground state. We find that the laser phase noise triggers severe heating of nanoparticles' motion along the optical lattice. When the laser phase noise is decreased by orders of magnitude, the heating rate is reduced and accordingly the occupation number is lowered to about three. We establish a model directly connecting the heating rate and the measured laser phase noise and elucidates that the occupation number under the lowest laser phase noise in our system is limited only by photon recoil heating. Our results show that the reduction of the laser phase noise near the oscillation frequency of nanoparticles is crucial for bringing them near the ground state and pave the way to sensitive accelerometers and quantum mechanical experiments with ultracold nanoparticles in an optical lattice.