Direct observation of swap cooling in atom–ion collisions

Amir Mahdian,Johannes Hecker Denschlag,Artjom Krükow

doi:10.1088/1367-2630/ac0575

Amir Mahdian, Johannes Hecker Denschlag + Show 1 more

Open Access

https://doi.org/10.1088/1367-2630/ac0575

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Abstract

Collisions with cold particles can dissipate a hot particle’s energy and therefore can be exploited as a cooling mechanism. Kinetics teach us that cooling a particle down by several orders of magnitude typically takes many elastic collisions as each one only carries away a fraction of the collision energy. Recently, for a system comprising hot ions and cold atoms, a very fast cooling process has been suggested (Ravi et al 2012 Nat. Commun. 3 1126) where cooling over several orders of magnitude can occur in a single step. Namely, in a homo-nuclear atom–ion collision, an electron can resonantly hop from an ultracold atom onto the hot ion, converting the cold atom into a cold ion. Here, we demonstrate such swap cooling in a direct way as we experimentally observe how a single energetic ion loses energy in a cold atom cloud. In order to contrast swap cooling with sympathetic cooling, we perform the same measurements with a hetero-nuclear atom–ion system, for which swap cooling cannot take place, and indeed observe very different cooling dynamics. Ab initio numerical model calculations agree well with our measured data and corroborate our interpretations.

Highlights

The preparation of cold ions is often a precondition for modern experiments in various scientific fields, ranging from ultracold chemistry[2] to quantum information processing[3]
Ion Atom at rest Glancing collision at rest our experiments in a regime where sympathetic cooling via elastic collisions is negligible and the exchange of energy is attributed to swap cooling
We investigated how swap cooling depends on the initial kinetic energy of the ion and found agreement with theoretical predictions

Summary

Introduction

The preparation of cold ions is often a precondition for modern experiments in various scientific fields, ranging from ultracold chemistry[2] to quantum information processing[3]. We removed the atoms and slowly lowered the depth of the ion’s trapping potential in axial direction to a fixed value (see Appendix for the details), such that the ion would only stay in the trap and could be detected if its energy had been cooled to below ≈50 K×kB.

Results

Conclusion