Nuclear Spin Quenching of the S 2 1 / 2 → F 2 7 / 2 Electric Octupole Transition in Yb + 173

We report the coherent excitation of the highly forbidden ²S1/2→²F7/2 clock transition in the odd isotope ¹⁷³Yb⁺ with nuclear spin I=5/2, and reveal the hyperfine-state-dependent, nuclear-spin-induced quenching of this transition. The inferred lifetime of the Fₑ=4 hyperfine state is one order of magnitude shorter than the unperturbed ²F7/2 clock state of ¹⁷¹Yb⁺. This reduced lifetime lowers the required optical power for coherent excitation of the clock transition, thereby reducing the ac Stark shift caused by the clock laser. Using a three-ion Coulomb crystal, we experimentally demonstrate an approximately twentyfold suppression of the ac Stark shift, a critical improvement for the scalability of future multi-ion Yb⁺ clocks. Furthermore, we report the |²S1/2,Fg=3⟩→|²F7/2,Fₑ=6⟩ unquenched reference transition frequency as 642.11917656354(43) THz, along with the measured hyperfine splitting and calculated quadratic Zeeman sensitivities of the ²F7/2 clock state. Our results pave the way toward multi-ion optical clocks and quantum computers based on ¹⁷³Yb⁺.