Towards an optical clock with ¹⁷³Yb⁺ ions

Clocks based on optical reference transitions are the most accurate measurement devices ever built. Among them, the single-ion clock based on the ²S_1/2-²F_7/2 electric octupole transition of a ¹⁷¹Yb⁺ ion is one of the systems that have the lowest uncertainty [1]. A recent theoretical study shows that the coupling between the excited and ground states for this transition in ¹⁷³Yb⁺ isotope is significantly stronger [2]. Consequently, the radiative lifetime will be reduced from 1.6 years [3] to days. While the stronger coupling in 173Yb⁺ will largely reduce the light shift introduced when exciting the highly forbidden transition, the reduced lifetime in ¹⁷³Yb⁺ will still be significantly longer than any laser coherence time envisioned to date and hence enable very good clock stability. Here, we report on progress at PTB in cooling and trapping ¹⁷³Yb⁺ ions, and searching for clock transitions in this isotope with richer hyperfine structure (I=5/2).

[1] Sanner et al., Nature 567, 204 (2019).

[2] V. A. Dzuba and V. V. Flambaum, Phys. Rev. A 93, 052517 (2016).

[3] R. Lange, et al. Phys. Rev. Lett. 127 213001 (2021).