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Magneto-optical trapping and sub-Doppler cooling of a polyatomic molecule

Abstract

Laser cooling and trapping1,2, and magneto-optical trapping methods in particular2, have enabled groundbreaking advances in science, including Bose–Einstein condensation3,4,5, quantum computation with neutral atoms6,7 and high-precision optical clocks8. Recently, magneto-optical traps (MOTs) of diatomic molecules have been demonstrated9,10,11,12, providing access to research in quantum simulation13 and searches for physics beyond the standard model14. Compared with diatomic molecules, polyatomic molecules have distinct rotational and vibrational degrees of freedom that promise a variety of transformational possibilities. For example, ultracold polyatomic molecules would be uniquely suited to applications in quantum computation and simulation15,16,17, ultracold collisions18, quantum chemistry19 and beyond-the-standard-model searches20,21. However, the complexity of these molecules has so far precluded the realization of MOTs for polyatomic species. Here we demonstrate magneto-optical trapping of a polyatomic molecule, calcium monohydroxide (CaOH). After trapping, the molecules are laser cooled in a blue-detuned optical molasses to a temperature of 110 μK, which is below the Doppler cooling limit. The temperatures and densities achieved here make CaOH a viable candidate for a wide variety of quantum science applications, including quantum simulation and computation using optical tweezer arrays15,17,22,23. This work also suggests that laser cooling and magneto-optical trapping of many other polyatomic species24,25,26,27 will be both feasible and practical.

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Fig. 1: Laser cooling and repumping scheme.
Fig. 2: MOT lifetime versus number of states repumped.
Fig. 3: MOT dynamics and characteristics.
Fig. 4: Sub-Doppler cooling.

Data availability

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

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Acknowledgements

We acknowledge B. L. Augenbraun and Y. Bao for discussions, and thank S. Kotochigova and J. Kłos for providing theoretical insight into the CaOH chemical enhancement. This work was supported by the AFOSR and the NSF. N.B.V. acknowledges support from the NDSEG fellowship, and L.A. acknowledges support from the HQI.

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N.B.V., C.H., L.A., P.R., A.W. and D.M. designed and assembled the apparatus, discussed experimental protocols and performed the experiment. N.B.V., C.H. and L.A. analysed the data. J.M.D. supervised all work and contributed to setting the direction of the experiment, as well as the design and development of the experimental apparatus, methods and analysis of data. All authors discussed the results and contributed to the manuscript.

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Correspondence to Nathaniel B. Vilas.

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Extended Data Table 1 Repumping transitions driven for CaOH photon cycling and laser cooling

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Vilas, N.B., Hallas, C., Anderegg, L. et al. Magneto-optical trapping and sub-Doppler cooling of a polyatomic molecule. Nature 606, 70–74 (2022). https://doi.org/10.1038/s41586-022-04620-5

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