Postselection shifts the transition frequency of helium in an atomic beam.

Sci Adv

State Key Laboratory of Molecular Reaction Dynamics, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China.

Published: February 2025

Postselecting output states can effectively amplify weak signals in measurements. However, the postselection (PS) effect may also introduce unintended biases in precision measurements. Here, we investigate the influence of PS in the precision spectroscopy of the 2 - 2 transition of helium (He) using an atomic beam. We directly observe that PS based on atomic positions causes a shift in the measured transition frequency, amounting to approximately -55 kHz. After accounting for this PS shift, we obtain a corrected frequency of 276,764,094,712.45 ± 0.86 kHz for the 2 - 2 transition. Combining this result with existing data for He, we derive a value for the difference in squared nuclear charge radii, which shows a σ deviation from measurements of muonic helium ions, potentially pointing to new physics that challenges lepton universality in quantum electrodynamics.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC11870057PMC
http://dx.doi.org/10.1126/sciadv.adu9796DOI Listing

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