The suitability of the 411-nm 2S1/2-2D5/2 transition in Yb+ is assessed as an optical frequency standard. The lifetime of the 2D5/2 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 2D5/2 level can decay into the highly metastable 2F7/2 level where it is trapped. The branching ratio for decay into the 2F7/2 level has been measured and found to be 0.83±0.03. A transition capable of rapidly depopulating the 2F7/2 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 172Yb+ to be performed, yielding a center frequency of 729 476 869.13(0.42) MHz (1σ).
- clock transition
- single ytterbium ion