Search for new physics using isotope-shift spectroscopy with trapped ions*

Historically, precise atomic spectroscopy has led to new physics in many instances. Precision low-energy experiments may thus supplement high-energy and astrophysical approaches. It has been proposed to measure the isotope shifts in ions to probe new physics using King plots [1-3]. A King plot maps isotope shifts as points in a two-dimensional graph [4]. The Standard Model (SM) predicts in the leading order that the points in King plots should lie on a straight line if the atoms have no nuclear spin. Our recent experiment with two narrow S → D transitions in trapped Yb⁺ ions showed evidence for departure from the predicted linearity [5]. However, the contribution of higher-order corrections to the non-linearity within the SM complicates the test. The sources of the observed violation should be examined carefully to decouple the SM corrections arising from nuclear physics from possible new-physics contributions.

Our previous study compared the pattern of the measured non-linearity with the patterns that the particular models for the sources predict [5]. I will present our latest experiment, where the isotope shifts of the narrowest-known S → F transition in five Yb⁺ isotopes are measured with high precision. Having isotope shifts for more transitions and isotopes provides stronger tests of the SM and enables model-independent tests for the number of sources of the non-linearity. 

[1] J. C. Berengut et al., PRL 120 091801 (2018)

[2] V. V. Flambaum, A. J. Geddes, and A. V. Viatkina, PRA 97 032510 (2018)

[3] C. Delaunay et al., PRD 96 093001 (2017)

[4] W. H. King, Isotope Shifts in Atomic Spectra (Plenum Press, New York, 1984)

[5] I. Counts et al., PRL 125 123002 (2020)