High-Accuracy Optical Clock Based on the Octupole Transition inYb+171

Abstract

We experimentally investigate an optical frequency standard based on the 467 nm (642 THz) electric-octupole reference transition ${}^{2}S_{1/2}(F=0)\to {}^{2}F_{7/2}(F=3)$ in a single trapped ${}^{171}\mathrm{Yb}^{+}$ ion. The extraordinary features of this transition result from the long natural lifetime and from the $4f^{13}6s^2$ configuration of the upper state. The electric-quadrupole moment of the ${}^{2}F_{7/2}$ state is measured as $-0.041(5)e{a}_0^2$, where $e$ is the elementary charge and $a_0$ the Bohr radius. We also obtain information on the differential scalar and tensorial components of the static polarizability and of the probe-light-induced ac Stark shift of the octupole transition. With a real-time extrapolation scheme that eliminates this shift, the unperturbed transition frequency is realized with a fractional uncertainty of $7.1\times {10}^{-17}$. The frequency is measured as 642 121 496 772 645.15(52) Hz. DOI: http://dx.doi.org/10.1103/PhysRevLett.108.090801 © 2012 American Physical Society