Measurement of collisions between laser cooled cesium atoms and trapped cesium ions

TL;DR

This study measures the collision rate between ultracold cesium atoms and cesium ions in a hybrid trap, providing experimental data that aligns with theoretical predictions and also determining the photoionization cross section of cesium.

Contribution

The paper presents the first experimental measurement of the Cs-Cs+ collision rate coefficient in a hybrid trap, along with the determination of the cesium atom photoionization cross section at 473 nm.

Findings

Collision rate coefficient: 9.3 x 10^{-14} m^3/s

Photoionization cross section: 2.28 x 10^{-21} m^2

Agreement with theoretical calculations

Abstract

We report the measurement of collision rate coefficient for collisions between ultracold Cs atoms and low energy Cs+ ions. The experiments are performed in a hybrid trap consisting of a magneto-optical trap (MOT) for Cs atoms and a Paul trap for Cs+ ions. The ion-atom collisions impart kinetic energy to the ultracold Cs atoms resulting in their escape from the shallow MOT and, therefore, in a reduction in the number of Cs atoms in the MOT. By monitoring, using fluorescence measurements, the Cs atom number and the MOT loading dynamics and then fitting the data to a rate equation model, the ion-atom collision rate is derived. The Cs-Cs+ collision rate coefficient $9.3(\pm0.4)(\pm1.2)(\pm3.5) \times 10^{-14}$ m$^{3}$s$^{-1}$, measured for an ion distribution with most probable collision energy of 95 meV ($\approx k_{B}.1100$ K), is in fair agreement with theoretical calculations. As an intermediate step, we also determine the photoionization cross section of Cs $6P_{3/2}$ atoms at 473 nm wavelength to be $2.28 (\pm 0.33) \times 10^{-21}$ m$^{2}$.