Trapping molecular ions formed via photo-associative ionization of ultracold atoms

TL;DR

This paper reports the observation of $^{40}$Ca$_2^+$ molecular ions formed via two-photon photo-associative ionization of ultracold calcium atoms, providing a new method for producing ultracold molecular ions without additional lasers.

Contribution

It demonstrates a novel, laser-free technique for creating ultracold molecular ions through photo-associative ionization of ultracold atoms.

Findings

Observed formation of $^{40}$Ca$_2^+$ ions in a hybrid trap.

Calculated molecular potential curves for Ca$_2$ and Ca$_2^+$.

Estimated a lower bound for the two-photon rate constant.

Abstract

The formation of $^{40}$Ca$_2^+$ molecular ions is observed in a hybrid $^{40}$Ca magneto-optical and ion trap system. The molecular ion formation process is determined to be two-photon photo-associative ionization of ultracold $^{40}$Ca atoms. A lower bound for the two-body, two-photon rate constant is found to be $\bar{\beta} \geq 2 \pm 1 \times 10^{-15}$ cm$^{3}$ Hz. $\textit{Ab initio}$ molecular potential curves are calculated for the neutral Ca$_2$ and ionic Ca$_2^+$ molecules and used in a model that identifies the photo-associative ionization pathway. As this technique does not require a separate photo-association laser, it could find use as a simple, robust method for producing ultracold, state-selected molecular ions.