Postselection shifts the transition frequency of helium in an atomic beam.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 40020076.
- Also identified by DOI 10.1126/sciadv.adu9796 and PMC identifier 11870057.
- Licence recorded as CC BY-NC.
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Abstract
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<sup>3</sup><i>S</i> - 2<sup>3</sup><i>P</i> transition of helium (<sup>4</sup>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<sup>3</sup><i>S</i><sub>1</sub> - 2<sup>3</sup><i>P</i><sub>0</sub> transition. Combining this result with existing data for <sup>3</sup>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.