Abstract

Improvements in both theory and frequency metrology of few-electron systems such as hydrogen and helium have enabled increasingly sensitive tests of quantum electrodynamics, as well as ever more accurate determinations of fundamental constants and the size of the nucleus. At the same time, advances in cooling and trapping of neutral atoms have revolutionized the development of increasingly accurate atomic clocks. Here, we combine these fields to reach very high precision on an optical transition in the helium atom by employing a 4He Bose–Einstein condensate confined in a magic wavelength optical dipole trap. The measured transition accurately connects the ortho- and parastates of helium and constitutes a stringent test of quantum electrodynamics theory. In addition, we test polarizability calculations and ultracold scattering properties of the helium atom. Finally, our measurement lays the foundation for a determination of the 3He–4He nuclear charge radius difference with an accuracy exceeding that of muonic helium measurements currently being performed in the context of the proton radius puzzle.

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Acknowledgements

We would like to thank R. van der Beek for useful discussions and a critical reading of the manuscript, D. Cocks and I. Whittingham for helpful discussions, and R. Kortekaas for technical support. We gratefully acknowledge financial support from the Netherlands Organisation for Scientific Research (NWO).

Author information

Author notes

    • R. P. M. J. W. Notermans

    Present address: Department of Physics, Stanford University, Stanford, CA, USA

Affiliations

  1. LaserLaB, Department of Physics and Astronomy, Vrije Universiteit, Amsterdam, the Netherlands

    • R. J. Rengelink
    • , Y. van der Werf
    • , R. P. M. J. W. Notermans
    • , R. Jannin
    • , K. S. E. Eikema
    •  & W. Vassen
  2. Dodd-Walls Centre for Photonic and Quantum Technologies, Department of Physics, University of Auckland, Auckland, New Zealand

    • M. D. Hoogerland

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Contributions

R.J.R. and R.P.M.J.W.N. constructed the experimental set-up. R.J.R., Y.v.d.W. and M.D.H. performed the measurements. R.J.R., Y.v.d.W. and R.J. investigated systematic effects. R.J.R. performed the data analysis. R.J.R., R.P.M.J.W.N. and K.S.E.E. performed and discussed the frequency metrology. W.V. initiated and supervised the project. All authors discussed the results and contributed to the manuscript.

Competing interests

The authors declare no competing interests.

Corresponding author

Correspondence to W. Vassen.

Supplementary information

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    Supplementary Text, Figures S1, Table S1, and References

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DOI

https://doi.org/10.1038/s41567-018-0242-5