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 → 6d 2 D 5/2 electric quadrupole transition. By self-referencing three pairs of symmetric Zeeman transitions, we demonstrate a frequency instability of 1.1×10 −13 / √ τ , where τ is the averaging time in seconds. The total systematic uncertainty is evaluated to be ∆ν/ν = 9 × 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: gD/gS = 0.598 805 3(11) A Ra + optical clock could improve limits on the time variation of the fine structure constant, α/α, in an optical frequency comparison. The ion also has several features that make it a suitable system for a transportable optical clock.