Radium Ion Optical Clock

Abstract

We report the first operation of a Ra${}^{+}$ optical clock, a promising high-performance clock candidate. The clock uses a single trapped ${}^{226}$Ra${}^{+}$ ion and operates on the $7s{}^2{S}_{1/2}\to$ $6d{}^2{D}_{5/2}$ electric quadrupole transition. By self-referencing three pairs of symmetric Zeeman transitions, we demonstrate a frequency instability of 1.1$\times 10^{-13}$/$\sqrt{\tau }$, where $\tau$ is the averaging time in seconds. The total systematic uncertainty is evaluated to be $\Delta \nu /\nu =9\times 10^{-16}$. Using the clock, we realize the first measurement of the ratio of the $D_{5/2}$ state to the $S_{1/2}$ state Landé $g$-factors: $g_D/g_S$ = 0.5988053(11). A Ra${}^{+}$ optical clock could improve limits on the time variation of the fine structure constant, $\dot{\alpha }/\alpha$, in an optical frequency comparison. The ion also has several features that make it a suitable system for a transportable optical clock.

arXiv commentMain text 5 pages, 3 figures. Supplemental material 5 pages, 1 figure

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