Quantum electrodynamics (QED) is one of the most stringently tested theories underpinning modern physics. Nevdertheless, recent precision atomic spectroscopy measurements have uncovered several small discrepancies between experiment and theory. One particularly powerful experimental observable that tests QED independently of traditional energy level measurements is the tune-out frequency, where the dynamic polarizability vanishes and the atom does not interact with applied laser light. In our work, we measure the tune-out frequency for the $2\;^3S_1$ state of helium between transitions to the $2\;^3P_J$ and $3\;^3P_J$ manifolds and compare it with new theoretical QED calculations . The experimentally determined value of 725,736,700(260) MHz differs from theory [725,736,252(9) MHz] by 1.7 times the measurement uncertainty and resolves both the QED contributions and retardation corrections. The underlying theory is formulated more generally as a zero in the forward Rayleigh scattering cross section, rather than a zero in the dynamic polarizability. Relativistic, QED, and retardation corrections are included in a nonrelativistic QED (nr-QED) approach
 B. M. Henson et al., Science 376, 199 (2022).
|Presenter name||Gordon Drake|
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