Nuclear spin quenching of the ${}^2{S}_{1\mathrm{/}2}\to {}^2{F}_{7\mathrm{/}2}$ electric octupole transition in ${}^{173}$Yb${}^{+}$

We report the coherent excitation of the highly forbidden ${}^2{S}_{1\mathrm{/}2}\to {}^2{F}_{7\mathrm{/}2}$ clock transition in the odd isotope ${}^{173}{\mathrm{Y}\mathrm{b}}^{+}$ with nuclear spin $I=5\mathrm{/}2$, 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 ${}^2{F}_{7\mathrm{/}2}$ clock state of ${}^{171}{\mathrm{Y}\mathrm{b}}^{+}$. 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 3-ion Coulomb crystal, we experimentally demonstrate an approximately 20-fold suppression of the AC Stark shift, a critical improvement for the scalability of future multi-ion ${\mathrm{Y}\mathrm{b}}^{+}$ clocks. Furthermore, we report the ${\mathrm{\mid }}^2{S}_{1\mathrm{/}2},F_g=3⟩\to {\mathrm{\mid }}^2{F}_{7\mathrm{/}2},F_e=6⟩$ unquenched reference transition frequency as $642.11917656354(43)$ THz, along with the measured hyperfine splitting and calculated quadratic Zeeman sensitivities of the ${}^2{F}_{7\mathrm{/}2}$ clock state. Our results pave the way toward multi-ion optical clocks and quantum computers based on ${}^{173}{\mathrm{Y}\mathrm{b}}^{+}$.