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arXiv · 2506.16520

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

Charly Beulenkamp·Krzysztof P. Zamarski·Robert C. Bird·C. Ruth Le Sueur·Jeremy M. Hutson·Manuele Landini·Hanns-Christoph Nägerl
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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.

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Charly Beulenkamp, Krzysztof P. Zamarski, Robert C. Bird, C. Ruth Le Sueur, Jeremy M. Hutson, Manuele Landini, Hanns-Christoph Nägerl. 2025-06-19. Formation of ultracold $^{39}$K$^{133}$Cs Feshbach molecules. https://doi.org/10.1103/kqyr-mcx9

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