Evidence for the association of triatomic molecules in ultracold 23Na40K + 40K mixtures

Ultracold assembly of diatomic molecules has enabled great advances in controlled chemistry, ultracold chemical physics and quantum simulation with molecules(1-3). Extending the ultracold association totriatomic molecules will offer many new research opportunities and challenges in these fields. A possible approach is to form triatomic molecules in a mixture of ultracold atoms and diatomic molecules by using a Feshbach resonance between them(4,5). Although ultracold atom-diatomic-molecule Feshbach resonances have been observed recently(6,7), using these resonancesto form triatomic molecules remains challenging. Here we report on evidence ofthe association of triatomic molecules near the Feshbach resonance between (NaK)-Na-23-K-40 molecules in the rovibrational ground state and K-40 atoms. We apply a radio-frequency pulse to drive the free-bound transition in ultracold mixtures of (NaK)-Na-23-K-40 and K-40 and monitor the loss of (NaK)-Na-23-K-40 molecules. The association of triatomic molecules manifests itself as an additional loss feature in the radio-frequency spectra, which can be distinguished from the atomic loss feature. The observation that the distance between the association feature and the atomic transition changes with the magnetic field provides strong evidence for the formation of triatomic molecules. The binding energy of the triatomic molecules is estimated from the measurements. Our work contributes to the understanding of the complex ultracold atom-molecule Feshbach resonances and may open up an avenue towards the preparation and control of ultracold triatomic molecules.

Automated summary

The formation of triatomic molecules in mixtures of ultracold atoms and diatomic molecules using Feshbach resonance remains challenging. However, evidence of triatomic molecule association near the Feshbach resonance has been reported, and the binding energy of the triatomic molecules has been estimated.