Investigation of the2S1/2−2D5/2clock transition in a single ytterbium ion

The suitability of the 411-nm ${}^2{S}_{1/2}{-}^2{D}_{5/2}$ transition in ${\mathrm{Yb}}^{+}$ is assessed as an optical frequency standard. The lifetime of the ${}^2{D}_{5/2}$ level has been measured and found to be 7.2±0.3 ms, which implies a natural linewidth of 22.2±0.9 Hz for the 411-nm transition. In addition to a decay to the ground state the ${}^2{D}_{5/2}$ level can decay into the highly metastable ${}^2{F}_{7/2}$ level where it is trapped. The branching ratio for decay into the ${}^2{F}_{7/2}$ level has been measured and found to be 0.83±0.03. A transition capable of rapidly depopulating the ${}^2{F}_{7/2}$ level and returning the ion to the cooling cycle has been demonstrated. This has enabled a quantum jump measurement of the 411-nm transition in ${}^{172}{\mathrm{Yb}}^{+}$ to be performed, yielding a center frequency of 729 476 869.13(0.42) MHz (1σ).