Blue-sky bifurcation of ion energies and the limits of neutral-gas sympathetic cooling of trapped ions

TL;DR

This study investigates the fundamental limits of sympathetic cooling of trapped ions by neutral gases, revealing nonequilibrium bifurcations in ion temperature that constrain the creation of cold ion samples.

Contribution

It demonstrates the emergence of nonequilibrium bifurcations in ion steady-state temperatures, highlighting limitations in sympathetic cooling methods.

Findings

Observation of bifurcations in ion temperature with increasing ion number

Identification of nonequilibrium behavior in ion cooling dynamics

Limitations on maintaining cold ion samples using neutral gases

Abstract

Sympathetic cooling of trapped ions through collisions with neutral buffer gases is critical to a variety of modern scientific fields, including fundamental chemistry, mass spectrometry, nuclear and particle physics, and atomic and molecular physics. Despite its widespread use over four decades, there remain open questions regarding its fundamental limitations. To probe these limits, here we examine the steady-state evolution of up to ten barium ions immersed in a gas of three-million laser-cooled calcium atoms. We observe and explain the emergence of nonequilibrium behavior as evidenced by bifurcations in the ion steady-state temperature, parameterized by ion number. We show that this behavior leads to limitations in creating and maintaining translationally cold samples of trapped ions using neutral-gas sympathetic cooling. These results may provide a route to studying nonequilibrium thermodynamics.