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# Observation of Feshbach resonances between alkali and closed-shell atoms

## Abstract

Magnetic Feshbach resonances allow control of the interactions between ultracold atoms1. They are an invaluable tool in studies of few-body and many-body physics2,3, and can be used to convert pairs of atoms into molecules4,5 by ramping an applied magnetic field across a resonance. Molecules formed from pairs of alkali atoms have been transferred to low-lying states, producing dipolar quantum gases6. There is great interest in making molecules formed from an alkali atom and a closed-shell atom such as ground-state Sr or Yb. Such molecules have both a strong electric dipole and an electron spin; they will open up new possibilities for designing quantum many-body systems7,8, and for tests of fundamental symmetries9. The crucial first step is to observe Feshbach resonances in the corresponding atomic mixtures. Very narrow resonances have been predicted theoretically10,11,12, but until now have eluded observation. Here we present the observation of magnetic Feshbach resonances of this type, for an alkali atom, Rb, interacting with ground-state Sr.

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## Acknowledgements

This project has received funding from the European Research Council (ERC) under the European Union’s Seventh Framework Programme (FP7/2007-2013) (Grant agreement No. 615117 QuantStro). B.P. thanks the NWO for funding through Veni grant No. 680-47-438. P.S.$$\dot{{\rm{Z}}}$$. thanks the National Science Center for support from grant 2017/25/B/ST4/01486. J.M.H. thanks the UK Engineering and Physical Sciences Research Council for support under Grant No. EP/P01058X/1.

## Author information

Authors

### Contributions

V.B., A.C. and L.R. performed the experiments. B.P. and F.S. supervised the experimental work. P.S.$$\dot{{\rm{Z}}}$$. and J.M.H. contributed theoretical analysis. All authors were involved in analysis and discussions of the results and contributed to the preparation of the manuscript.

### Corresponding author

Correspondence to Florian Schreck.

## Ethics declarations

### Competing interests

The authors declare no conflict of interest.

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## Supplementary information

### Supplementary Information

Supplementary Information

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Reprints and Permissions

Barbé, V., Ciamei, A., Pasquiou, B. et al. Observation of Feshbach resonances between alkali and closed-shell atoms. Nature Phys 14, 881–884 (2018). https://doi.org/10.1038/s41567-018-0169-x

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• ### Quo vadis now, cold molecules?

• Paul S. Julienne

Nature Physics (2018)