Creation of an ultracold gas of triatomic molecules from an atom–diatomic molecule mixture

In recent years, there has been notable progress in the preparation and control of ultracold gases of diatomic molecules. The next experimental challenge is the production of ultracold polyatomic molecular gases. Here, we report the creation of an ultracold gas of 23Na40K2 triatomic molecules from a mixture of ground-state sodium-23–potassium-40 (23Na40K) molecules and potassium-40 (40K) atoms. The triatomic molecules were created by adiabatic magneto-association through an atom–diatomic molecule Feshbach resonance. We obtained clear evidence for the creation of triatomic molecules by directly detecting them using radio-frequency dissociation. Approximately 4000 triatomic molecules with a high-peak phase-space density of 0.05 could be created. The ultracold triatomic molecules can serve as a launchpad to probe the three-body potential energy surface and may be used to prepare quantum degenerate triatomic molecular gases. Description Forming dense, ultracold triatomic gases After the successful creation of ultracold diatomic molecular gases, the next grand experimental challenge is to prepare and control ultracold gases of triatomic molecules. Because they have more degrees of freedom, these gases offer many exciting research opportunities for molecular precision spectroscopy and quantum simulations. Using adiabatic magneto-association by ramping the magnetic field through a Feshbach resonance between 23Na40K and 40K, Yang et al. created an ultracold gas of weakly bound 23Na40K2 triatomic molecules at about 100 nanokelvin, as confirmed by their direct detection using the radiofrequency dissociation. About 4000 triatomic molecules were created with a high peak density 10 orders of magnitude higher than the best results previously reported, representing an important milestone in ultracold chemistry and physics. —YS Ultracold NaK dimers and K atoms can be coherently converted to NaK2 trimers at 100 nanokelvin, preserving a high phase space density.