Measurement of low-energy Na^+ -- Na total collision rate in an ion--neutral hybrid trap

TL;DR

This paper measures the collision rate between cold sodium atoms and ions in a hybrid trap, confirming theoretical predictions and demonstrating a new method to probe ion cloud distributions using a MOT.

Contribution

The study provides the first experimental measurements of Na^+ -- Na collision rates at low energies, aligning with theoretical calculations, and introduces a MOT-based technique for probing ion cloud spatial distributions.

Findings

Measured collision rate coefficients for Na^+ -- Na interactions.

Confirmed agreement with theoretical ab initio calculations.

Demonstrated MOT as a tool to probe ion cloud distribution.

Abstract

We present measurements of the total elastic and resonant charge-exchange ion-atom collision rate coefficient $k_\mathrm{ia}$ of cold sodium (\ce{Na}) with optically-dark low energy \ce{Na+} ions in a hybrid ion-neutral trap. To determine $k_\mathrm{ia}$, we measured the trap loading and loss from both a \ce{Na} magneto-optical trap (MOT) and a linear radio frequency quadrupole Paul trap. We found the total rate coefficient to be $7.4 \pm 1.9 \times 10^{-8}$ cm$^3$/s for the type I \ce{Na} MOT immersed within an $\approx 140$ K ion cloud and $1.10 \pm 0.25 \times 10^{-7}$ cm$^3$/s for the type II \ce{Na} MOT within an $\approx 1070$ K ion cloud. Our measurements show excellent agreement with previously reported theoretical fully quantal \textit{ab initio} calculations. In the process of determining the total rate coefficient, we demonstrate that a MOT can be used to probe an optically dark ion cloud's spatial distribution within a hybrid trap.