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Laser-induced forced evaporative cooling of molecular anions below 4 K

Nature Physics volume 19, pages 1270–1274 (2023)Cite this article

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Abstract

The study of cold and controlled molecular ions has been of key importance for a wide range of applications, such as the production of cold antihydrogen, creation and study of anionic Coulomb crystals and in atmospheric research and astrochemistry. However, the commonly used anion cooling technique via collisions with a buffer gas is limited by the temperature of the used cryogenic cooling medium. Here we demonstrate the forced evaporative cooling of anions via a laser beam with photon energies far above the photodetachment threshold of the anion. We cool an anionic ensemble from an initial temperature of 370(12) K down to 2.2(8) K. This results in a three orders of magnitude increase in the phase-space density of the ions, approaching the near-strong Coulomb coupling regime. We present an analysis of the cooling dynamics through a thermodynamic model that includes the role of intrinsic collisional heating, without any fitting parameters. This technique can be used to cool any anionic species below liquid helium temperature, providing a tool to push the frontiers of anion cooling below state-of-the-art temperature regimes.

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Fig. 1: Experimental setup and thermalization dynamics under position-dependent photodetachment.
Fig. 2: Forced evaporative cooling via photodetachment.

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Data availability

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

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The codes and analysis files that support the findings of this study are available from the corresponding author upon request.

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Acknowledgements

This work is supported by the Deutsche Forschungsgemeinschaft (DFG) under project no. WE/2661/14-1 and the Austrian Science Fund (FWF) through project no. I3159-N36. M.W. acknowledges support from the DFG (German Research Foundation) under Germany’s Excellence Strategy EXC2181/1-390900948 (the Heidelberg STRUCTURES Excellence Cluster).

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Authors and Affiliations

  1. Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany

    Jonas Tauch, Saba Z. Hassan & Matthias Weidemüller

  2. Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria

    Markus Nötzold, Eric S. Endres & Roland Wester

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  1. Jonas Tauch
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  2. Saba Z. Hassan
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Contributions

J.T. and S.Z.H. performed the experiments and data analysis. J.T. simulated the thermodynamical model. M.N. provided the simulations on temperature determination. E.S.E., R.W. and M.W. conceptualized the experiments. J.T. and S.Z.H. wrote the initial draft. All the authors edited and contributed in the preparation of the final manuscript.

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Correspondence to Matthias Weidemüller.

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Nature Physics thanks Daniel Comparat and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Sections I–III, Figs. 1–3 and Table 1.

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Tauch, J., Hassan, S.Z., Nötzold, M. et al. Laser-induced forced evaporative cooling of molecular anions below 4 K. Nat. Phys. 19, 1270–1274 (2023). https://doi.org/10.1038/s41567-023-02084-6

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