Collisions of ultracold ^{23}Na^{87}Rb molecules with controlled chemical reactivities

TL;DR

This study reports the creation of ultracold ground-state NaRb molecules and investigates their collision behaviors, revealing unexpected similarities in loss rates regardless of chemical reactivity and highlighting the need for better understanding of short-range physics.

Contribution

First experimental creation of optically trapped ground-state NaRb molecules with controlled internal states and detailed collision analysis at ultracold temperatures.

Findings

Observed similar loss and heating rates regardless of chemical reactivity.

Loss rate constants decrease with increasing temperature, outside the Wigner regime.

Results semi-quantitatively match long-range interaction models, indicating complex short-range physics.

Abstract

The collision of molecules at ultracold temperatures is of great importance for understanding the chemical interactions at the quantum regime. While much theoretical work has been devoted to this, experimental data are only available sparsely mainly due to the difficulty in producing ground-state molecules at ultracold temperatures. We report here the creation of optically trapped samples of ground-state bosonic sodium-rubidium molecules with precisely controlled internal states and, enabled by this, a detailed study on the inelastic loss with and without the NaRb + NaRb $\rightarrow$ Na$_2$ + Rb$_2$ chemical reaction. Contrary to intuitive expectations, we observed very similar loss and heating, regardless of the chemical reactivities. In addition, as evidenced by the reducing loss rate constants with increasing temperatures, we found that these collisions are already outside the Wigner region even though the sample temperatures are sub-microkelvin. Our measurement agrees semi-quantitatively with models based on long-range interactions, but calls for a deeper understanding on the short-range physics for a more complete interpretation.