Measurement of collisions between rubidium atoms and optically dark rubidium ions

TL;DR

This study measures the collision rate between laser-cooled rubidium atoms and dark rubidium ions in a combined trap, providing a new method to quantify ion-atom interactions in cold atom experiments.

Contribution

A novel experimental technique and theoretical model are developed to directly measure the ion-atom collision rate coefficient in a cold atom-ion mixture.

Findings

Measured collision rate coefficient between Rb atoms and Rb+ ions.

Developed a rate equation model for atom loss dynamics.

Demonstrated systematic study of atom loss mechanisms.

Abstract

We measure the collision rate coefficient between laser cooled Rubidium (Rb) atoms in a magneto-optical trap (MOT) and optically dark Rb+ ions in an overlapping Paul trap. In such a mixture, the ions are created from the MOT atoms and allowed to accumulate in the ion trap, which results in a significant reduction in the number of steady state MOT atoms. A theoretical rate equation model is developed to describe the evolution of the MOT atom number, due to ionization and ion-atom collision, and derive an expression for the ion-atom collision rate coefficient. The loss of MOT atoms is studied systematically, by sequentially switching on the various mechanisms in the experiment. Combining the measurements with the model allows the direct determination of the ion-atom collision rate coefficient. Finally the scope of the experimental technique developed here is discussed.