Nuclear Spin Quenching of the ^{2}S_{1/2}→^{2}F_{7/2} Electric Octupole Transition in ^{173}Yb^{+}

We report the coherent excitation of the highly forbidden ^{2}S_{1/2}→^{2}F_{7/2} clock transition in the odd isotope ^{173}Yb^{+} with nuclear spin I=5/2, and reveal the hyperfine-state-dependent, nuclear-spin-induced quenching of this transition. The inferred lifetime of the F_{e}=4 hyperfine state is one order of magnitude shorter than the unperturbed ^{2}F_{7/2} clock state of ^{171}Yb^{+}. 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 |^{2}S_{1/2},F_{g}=3⟩→|^{2}F_{7/2},F_{e}=6⟩ unquenched reference transition frequency as 642.11917656354(43) THz, along with the measured hyperfine splitting and calculated quadratic Zeeman sensitivities of the ^{2}F_{7/2} clock state. Our results pave the way toward multi-ion optical clocks and quantum computers based on ^{173}Yb^{+}.