Superstatistical velocity distributions of cold trapped ions in molecular dynamics simulations

TL;DR

This paper uses detailed molecular dynamics simulations to study how infrequent collisions cause heating and superstatistical velocity distributions in laser-cooled ions within radiofrequency traps, impacting experimental measurements.

Contribution

It introduces a realistic simulation approach that avoids simplifying assumptions, revealing the impact of rare collisions on ion temperature and velocity distributions.

Findings

Infrequent collisions cause significant heating of ion ensembles.

Velocity distributions exhibit superstatistical behavior due to temperature fluctuations.

Implications for accurate ion temperature measurement and reaction rate determination.

Abstract

We present a realistic molecular-dynamics treatment of laser-cooled ions in radiofrequency ion traps which avoids previously made simplifications such as modeling laser cooling as a friction force and combining individual heating mechanisms into a single effective heating force. Based on this implementation, we show that infrequent energetic collisions of single ions with background gas molecules lead to pronounced heating of the entire ion ensemble and a time-varying secular ensemble temperature which manifests itself in a superstatistical time-averaged velocity distribution of the ions. The effect of this finding on the experimental determination of ion temperatures and rate constants for cold chemical reactions is discussed.