Micromotion-induced Limit to Atom-Ion Sympathetic Cooling in Paul Traps

TL;DR

This paper derives an analytic expression for a fundamental limit to atom-ion sympathetic cooling in Paul traps caused by trap-induced collisional heating, which prevents reaching quantum regimes in current experiments.

Contribution

The authors identify and analytically describe a fundamental heating limit in atom-ion cooling within Paul traps, highlighting the impact of trap electric fields on cooling efficiency.

Findings

Collisional heating prevents reaching the s-wave regime.

Conditions on mass ratio and trap parameters for quantum regime access.

Analytic expressions for the cooling limit derived.

Abstract

We present and derive analytic expressions for a fundamental limit to the sympathetic cooling of ions in radio-frequency traps using cold atoms. The limit arises from the work done by the trap electric field during a long-range ion-atom collision and applies even to cooling by a zero-temperature atomic gas in a perfectly compensated trap. We conclude that in current experimental implementations this collisional heating prevents access to the regimes of single-partial-wave atom-ion interaction or quantized ion motion. We determine conditions on the atom-ion mass ratio and on the trap parameters for reaching the s-wave collision regime and the trap ground state.