Ion dynamics in a linear radio-frequency trap with a single cooling laser

TL;DR

This study investigates the feasibility of cooling ions with a single laser beam in a linear RF trap by analyzing ion dynamics and Coulomb coupling effects through molecular dynamics simulations.

Contribution

It demonstrates how Coulomb interactions enable cooling of all ion motion components with a single laser in a linear RF trap, considering full RF potential effects.

Findings

Coulomb coupling efficiency depends on ion cloud geometry.

Full RF potential effects differ from pseudo-potential approximations.

Three-dimensional ion clouds achieve uniform temperature across motion components.

Abstract

We analyse the possibility of cooling ions with a single laser beam, due to the coupling between the three components of their motion induced by the Coulomb interaction. For this purpose, we numerically study the dynamics of ion clouds of up to 140 particles, trapped in a linear quadrupole potential and cooled with a laser beam propagating in the radial plane. We use Molecular Dynamics simulations and model the laser cooling by a stochastic process. For each component of the motion, we systematically study the dependence of the temperature with the anisotropy of the trapping potential. Results obtained using the full radio-frequency (rf) potential are compared to those of the corresponding pseudo-potential. In the rf case, the rotation symmetry of the potential has to be broken to keep ions inside the trap. Then, as for the pseudo-potential case, we show that the efficiency of the Coulomb coupling to thermalize the components of motion depends on the geometrical configuration of the cloud. Coulomb coupling appears to be not efficient when the ions organise as a line or a pancake and the three components of motion reach the same temperature only if the cloud extends in three dimensions.