Chemical Reaction of Ultracold Atoms and Ions in a Hybrid Trap

TL;DR

This paper reports the observation and measurement of a chemical reaction between ultracold Yb+ ions and Ca atoms in a hybrid trap, providing experimental data and theoretical insights into low-temperature ion-atom interactions relevant to quantum physics and astrophysics.

Contribution

First experimental measurement of ultracold Yb+ and Ca atom reactions with theoretical modeling, revealing reaction rates much higher than previous heteronuclear systems.

Findings

Measured reaction rate constant of (2±1.3)×10⁻¹⁰ cm³/s at 1 mK to 10 K

Reaction rate is four orders of magnitude higher than other heteronuclear cases

Provided explanation for discrepancies in radiative association predictions

Abstract

Interactions between cold ions and atoms have been proposed for use in implementing quantum gates\cite{Idziaszek2007}, probing quantum gases\cite{Sherkunov2009}, observing novel charge-transport dynamics\cite{Cote2000}, and sympathetically cooling atomic and molecular systems which cannot be laser cooled\cite{Smith2005,Hudson2009}. Furthermore, the chemistry between cold ions and atoms is foundational to issues in modern astrophysics, including the formation of stars, planets, and interstellar clouds\cite{Smith1992}, the diffuse interstellar bands\cite{Reddy2010}, and the post-recombination epoch of the early universe\cite{Stancil1996b}. However, as pointed out in refs 9 and 10, both experimental data and a theoretical description of the ion-atom interaction at low temperatures, reached in these modern atomic physics experiments and the interstellar environment, are still largely missing. Here we observe a chemical reaction between ultracold $^{174}$Yb$^+$ ions and $^{40}$Ca atoms held in a hybrid trap. We measure, and theoretically reproduce, a chemical reaction rate constant of $ \rm \bf K =(2\pm1.3)\times10^{-10} cm^{3}s^{-1}$ for $ \rm \bf 1 mK \leq T \leq 10 K$, four orders of magnitude higher than reported for other heteronuclear cases. We also offer a possible explanation for the apparent contradiction between typical theoretical predictions and measurements of the radiative association process in this and other systems.