# Electric feedback cooling of single charged nanoparticles in an optical trap

## TL;DR

This paper demonstrates electric feedback cooling of single charged nanoparticles in an optical trap, achieving millikelvin temperatures and surpassing conventional optical cooling methods, enabling quantum studies.

## Contribution

The study introduces a feedback cooling technique using electric fields for charged nanoparticles, achieving lower temperatures than traditional optical methods.

## Key findings

- Achieved sub-10 mK temperatures at low pressure.
- Validated charge estimation via frequency shift measurements.
- Demonstrated cooling efficiency surpassing optical methods.

## Abstract

We demonstrate feedback cooling of the center-of-mass motion of single charged nanoparticles to millikelvin temperatures in three dimensions via applying oscillating electric fields synchronized to their optically observed motion. The observed motional temperatures at weak feedback agree with a simple model and allow us to estimate the charge number of trapped nanoparticles. The agreement between our model and experiments is confirmed by independent measurements of the charge numbers based on a shift in the oscillation frequency induced by a constant electric field. The demonstrated temperature of below 10 mK at $4 \times 10^{-3}$ Pa is lower than that with the conventional optical cooling approach at this pressure by one to two orders of magnitude. Our results form the basis of manipulating cold charged nanoparticles and paves the way to quantum mechanical studies with trapped nanoparticles near their ground state.