Isotope-Shift Measurement of Bosonic Yb⁺ Ions

We present a method that the atomic transition frequency measurement relies on the accurate wavemeter, optical frequency comb and stable Fabry–Pérot cavity to precise determination of stable even isotope shift on single Yb⁺ ion (A = 168, 170, 172, 174, 176). The 6s²S_1/2 ↔ 6p²P_1/2 and 5d²D_3/2 ↔ 6s³3/2_1/2 resonance dipole transition frequencies are preliminarily measured by using a wavemeter which is calibrated by the 729 nm clock laser of ⁴⁰Ca⁺. Meanwhile, those frequencies are double checked by using optical frequency comb for correction of deviation. Ultimately, by changing frequency locking points at an ultralow expansion cavity more slightly and monitoring the corresponding atomic fluorescence changing with 17%, we finally improve the resonant frequency uncertainty to ±6 MHz, which is one order of improvement in precision higher than previously published measurements on the same transitions. A King-plot analysis with sensitivity to coupling between electrons and neutrons is carried out to determine the field and mass shift constants. Our measurement combined with existing or future isotope shift measurements can be used to determine basic properties of atomic nuclei, and to test new forces beyond the Standard Model.