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Raman sideband cooling of molecules in an optical tweezer array

Nature Physics volume 20, pages 389–394 (2024)Cite this article

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Abstract

Ultracold molecules have been proposed as a candidate platform for quantum science and precision measurement because of their rich internal structures and interactions. Direct laser-cooling promises to be a rapid and efficient way to bring molecules to ultracold temperatures. However, for trapped molecules, laser-cooling to the quantum motional ground state remains an outstanding challenge. A technique capable of reaching the motional ground state is Raman sideband cooling, first demonstrated in trapped ions and atoms. Here we demonstrate Raman sideband cooling of CaF molecules trapped in an optical tweezer array. Our protocol does not rely on high magnetic fields and preserves the purity of molecular internal states. We measure a high ground-state fraction and achieve low motional entropy per particle. The low temperatures we obtain could enable longer coherence times and higher-fidelity molecular qubit gates, desirable for quantum information processing and quantum simulation. With further improvements, Raman sideband cooling will also provide a route to quantum degeneracy of large molecular samples, which could be extendable to polyatomic molecular species.

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Fig. 1: Raman sideband cooling scheme.
Fig. 2: Raman linewidths and optical pumping characterization.
Fig. 3: Raman sideband spectra at θ = 0° and adiabatic trap lowering curves.
Fig. 4: Raman thermometry.

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Data availability

Data for figures in the Supplementary Information are available from Dryad54. Additional experimental data are available from the corresponding authors upon reasonable request. Source data are provided with this paper.

Code availability

The code used in this manuscript is available from the corresponding author upon reasonable request.

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Acknowledgements

We thank J. Thompson, W. Bakr and the Bakr group for fruitful discussions. This work is supported by the National Science Foundation (grant no. 2207518) and by the Sloan Research Foundation (grant no. FG-2022-19104). C.M.H. acknowledges support from a Joseph Taylor Graduate Student Fellowship. S.J.L. acknowledges support from a Princeton Quantum Initiative Graduate Student Fellowship.

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  1. These authors contributed equally: Yukai Lu, Samuel J. Li, Connor M. Holland.

Authors and Affiliations

  1. Department of Physics, Princeton University, Princeton, NJ, USA

    Yukai Lu, Samuel J. Li, Connor M. Holland & Lawrence W. Cheuk

  2. Department of Electrical and Computer Engineering, Princeton University, Princeton, NJ, USA

    Yukai Lu

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L.W.C. conceived the study and supervised the experiment. Y.L., C.M.H. and S.J.L. performed the experiments and the data analysis. All authors contributed to the manuscript.

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Correspondence to Lawrence W. Cheuk.

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Lu, Y., Li, S.J., Holland, C.M. et al. Raman sideband cooling of molecules in an optical tweezer array. Nat. Phys. 20, 389–394 (2024). https://doi.org/10.1038/s41567-023-02346-3

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