Counts Ian, Hur Joonseok, Aude Craik Diana P L, Jeon Honggi, Leung Calvin, Berengut Julian C, Geddes Amy, Kawasaki Akio, Jhe Wonho, Vuletić Vladan
Department of Physics and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea.
Phys Rev Lett. 2020 Sep 18;125(12):123002. doi: 10.1103/PhysRevLett.125.123002.
We measure isotope shifts for five Yb^{+} isotopes with zero nuclear spin on two narrow optical quadrupole transitions ^{2}S_{1/2}→^{2}D_{3/2}, ^{2}S_{1/2}→^{2}D_{5/2} with an accuracy of ∼300 Hz. The corresponding King plot shows a 3×10^{-7} deviation from linearity at the 3σ uncertainty level. Such a nonlinearity can indicate physics beyond the Standard Model (SM) in the form of a new bosonic force carrier, or arise from higher-order nuclear effects within the SM. We identify the quadratic field shift as a possible nuclear contributor to the nonlinearity at the observed scale, and show how the nonlinearity pattern can be used in future, more accurate measurements to separate a new-boson signal from nuclear effects.
