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Collisionally stable gas of bosonic dipolar ground-state molecules

Nature Physics volume 19, pages 1579–1584 (2023)Cite this article

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Abstract

Stable ultracold ensembles of dipolar molecules hold great promise for studies of many-body quantum physics, but high inelastic loss rates have been a long-standing challenge. Recently, gases of fermionic molecules in their ground state have been effectively stabilized by applying external fields. However, for gases of bosonic molecules, which might provide access to fundamentally different many-body quantum systems, it is unknown whether a similar suppression of losses can be achieved. This is due to the high inelastic loss rates for bosonic molecules, which are intrinsically one to two orders of magnitude larger than those for their fermionic counterparts. Here we stabilize a bosonic gas of strongly dipolar NaCs molecules via microwave shielding, decreasing losses by more than a factor of 200 and reaching lifetimes on the order of 1 second. In addition, we measure high elastic scattering rates and characterize their anisotropy, which arises from strong dipolar interactions. Finally, we demonstrate evaporative cooling of a bosonic molecular gas. We increase the phase-space density by a factor of 20, reach a temperature of 36(5) nK and bring the system to the brink of quantum degeneracy. Our results constitute a step towards the creation of a Bose–Einstein condensate of dipolar molecules and open the door to the creation of strongly correlated phases of dipolar quantum matter.

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Fig. 1: Microwave shielding of NaCs molecules.
Fig. 2: Lifetime and inelastic collisions of microwave-shielded NaCs molecules.
Fig. 3: Elastic collisions of microwave-shielded NaCs molecules.
Fig. 4: Evaporation of microwave-dressed molecules at Ω/(2π) = 4 MHz and Δ/(2π) = 6 MHz.

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Data availability

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

Code availability

All relevant codes are available from the corresponding author upon reasonable request.

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Acknowledgements

We thank A. Schindewolf, G. Quéméner and T. Hilker for helpful discussions, M. Lipson and J. Shabani for the loan of equipment and T. Yefsah for critical reading of the paper. This work was supported by an NSF CAREER Award (award no. 1848466), an ONR DURIP Award (award no. N00014-21-1-2721) and a Lenfest Junior Faculty Development Grant from Columbia University. C.W. acknowledges support from the Natural Sciences and Engineering Research Council of Canada (NSERC). W.Y. acknowledges support from the Croucher Foundation. I.S. was supported by the Ernest Kempton Adams Fund. S.W. acknowledges additional support from the Alfred P. Sloan Foundation.

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Authors and Affiliations

  1. Department of Physics, Columbia University, New York, NY, USA

    Niccolò Bigagli, Claire Warner, Weijun Yuan, Siwei Zhang, Ian Stevenson & Sebastian Will

  2. Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands

    Tijs Karman

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Contributions

All authors contributed substantially to the work presented in this paper. N.B., C.W., W.Y., S.Z. and I.S. carried out the experiments and improved the experimental set-up. T.K. performed the theoretical calculations. S.W. supervised the study. All authors contributed to the data analysis and writing of the paper.

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Correspondence to Sebastian Will.

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Extended data

Extended Data Fig. 1 Time-of-flight expansion of a gas of NaCs ground state molecules with shielding.

Time-of-flight expansion of a gas of ground state molecules with shielding at Ω/(2π) = 4 MHz, Δ/(2π) = 6 MHz. Upper (lower) panels correspond to the x (y) direction. Insets in the lower panels illustrate the experimental sequence. The fitted mean temperature is 290(10) nK.

Extended Data Fig. 2 Fitting an s-wave scattering length.

a, Comparison of experimentally extracted collision cross-section, assuming Ncol = 1, to the calculated ratio of the elastic cross-section and \({N}_{{{{\rm{col}}}}}^{{{{\rm{xz}}}}}\). Solid line corresponds to as = 1200 a0 while the dashed line is obtained directly from our coupled-channels calculations. The error bars provided are the 1σ error from the fit of the thermalization curves. b, Comparison of calculated \({N}_{{{{\rm{col}}}}}^{{{{\rm{xz}}}}}\) for as = 1200 a0, orange solid line, and \({a}_{s}=\bar{a}\), orange dashed line. The black dashed line marks Ncol = 2.5.

Supplementary information

Supplementary Information

Supplementary Figs. 1–5 and Discussion.

Source data

Source Data

Data for plots in Figs. 1–4.

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Bigagli, N., Warner, C., Yuan, W. et al. Collisionally stable gas of bosonic dipolar ground-state molecules. Nat. Phys. 19, 1579–1584 (2023). https://doi.org/10.1038/s41567-023-02200-6

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