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# Tuning of dipolar interactions and evaporative cooling in a three-dimensional molecular quantum gas

## Abstract

Ultracold polar molecules possess long-range, anisotropic and tunable dipolar interactions, providing opportunities to probe quantum phenomena that are inaccessible with existing cold gas platforms. However, experimental progress has been hindered by the dominance of two-body loss over elastic interactions, which prevents efficient evaporative cooling. Although recent work has demonstrated controlled interactions by confining molecules to a two-dimensional geometry, a general approach for tuning molecular interactions in a three-dimensional stable system has been lacking. Here we demonstrate tunable elastic dipolar interactions in a bulk gas of ultracold 40K87Rb molecules in three dimensions, facilitated by an electric field-induced shielding resonance that suppresses the reactive loss by a factor of 30. This improvement in the ratio of elastic to inelastic collisions enables direct thermalization. The thermalization rate depends on the angle between the collisional axis and the dipole orientation controlled by an external electric field, a direct manifestation of the anisotropic dipolar interaction. We achieve evaporative cooling mediated by the dipolar interactions in three dimensions. This work demonstrates full control of a long-lived bulk quantum gas system with tunable long-range interactions, paving the way for the study of collective quantum many-body physics.

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## Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request. Source data are provided with this paper.

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## Acknowledgements

We acknowledge funding from ARO-MURI, AFOSR-MURI, DARPA DRINQS, NSF QLCI OMA–2016244, NIST, and NSF grant no. 1806971. L.L. and G.Q. acknowledge funding from FEW2MANY-SHIELD project no. ANR-17-CE30-0015 from Agence Nationale de la Recherche. We thank L. R. Liu for reading the manuscript.

## Author information

Authors

### Contributions

J.-R.L., W.G.T., K.M., C.M., G.V., L.D.M. and J.Y. contributed to the experimental measurements. L.L. and G.Q. calculated the effective intermolecular potential. R.R.W.W. and J.L.B. calculated the anisotropic thermalization rate. All authors discussed the results, contributed to the data analysis and worked on the manuscript.

### Corresponding authors

Correspondence to Jun-Ru Li or Jun Ye.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

## Extended data

### Extended Data Fig. 1 Fitting experimental data with the model.

The figure shows the fit results for θ = 45°. a, Fitting of the unheated and heated data. b, Fitted KL and Ncoll for 100 synthetic datasets. We extract a correlation of −0.26 between the two fitted parameters, indicating that the fitting can distinguish between two-body loss and thermalization. The black solid lines are the median of all the fitted results from the synthetic datasets for Ncoll and KL, while the gray lines on the axis represent 68% confidence interval of the fitted results. This median and 68% confidence are reported in the main text. c, Extracted loss coefficient KL versus θ. The line and shaded region indicate the mean value of KL and its standard error.

## Supplementary information

### Supplementary Information

Supplementary Fig. 1 and Sections 1 and 2.

Source data.

Source data.

Source data.

Source data.

Source data.

## Rights and permissions

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Li, JR., Tobias, W.G., Matsuda, K. et al. Tuning of dipolar interactions and evaporative cooling in a three-dimensional molecular quantum gas. Nat. Phys. 17, 1144–1148 (2021). https://doi.org/10.1038/s41567-021-01329-6

• Accepted:

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• DOI: https://doi.org/10.1038/s41567-021-01329-6

• ### Evaporation of microwave-shielded polar molecules to quantum degeneracy

• Andreas Schindewolf
• Roman Bause
• Xin-Yu Luo

Nature (2022)

• ### Impact of GO on Non-stoichiometric Mg0.85 K0.3Fe2O4 Ferrite Nanoparticles

• Ebtesam E. Ateia
• Asmaa Abd Allah