Formation of ultracold $^{39}$K$^{133}$Cs Feshbach molecules

TL;DR

This paper reports the creation and characterization of ultracold $^{39}$K$^{133}$Cs molecules, demonstrating a cooling method, Feshbach molecule formation, and improved interaction potentials, advancing the field of ultracold molecular gases.

Contribution

The study introduces a new cooling strategy and detailed Feshbach spectroscopy for $^{39}$K$^{133}$Cs, improving interaction models for future ground-state molecule production.

Findings

Produced ultracold $^{39}$K$^{133}$Cs molecules with 7.6×10^3 count

Observed new interspecies Feshbach resonances

Fitted interaction potentials for better molecule control

Abstract

We report the creation of an ultracold gas of bosonic $^{39}$K$^{133}$Cs molecules. We first demonstrate a cooling strategy relying on sympathetic cooling of $^{133}$Cs to produce an ultracold mixture. From this mixture, weakly bound molecules are formed using a Feshbach resonance at 361.7 G. The molecular gas contains $7.6(10)\times 10^3$ molecules with a lifetime of about 130 ms, limited by two-body decay. We perform Feshbach spectroscopy to observe several new interspecies resonances and characterize the bound state used for magnetoassociation. Finally, we fit the combined results to obtain improved K-Cs interaction potentials. This provides a good starting point for the creation of ultracold samples of ground-state $^{39}$K$^{133}$Cs molecules.