Abstract
An absolute frequency measurement has been made of the 2S1/2–2F7/2 electric octupole transition in a single ion of 171Yb+. The implementation of a diode-based probe laser stabilized to this highly forbidden transition has resulted in an improvement of more than one order of magnitude upon the lowest published uncertainty. After correcting for systematic shifts, the frequency was determined to be 642 121 496 772 646.22 (67) Hz. This corresponds to a fractional uncertainty of 1.0 × 10−15.
Highlights
Optical frequency standards offer the possibility of making a step improvement of more than two orders of magnitude in the stability and accuracy of the realization of the SI second
Candidates for optical frequency standards based on single trapped ions or neutral atoms confined in optical lattice potentials are being investigated worldwide [3]
Systems based on single ions tightly confined in radio-frequency potentials have the advantage of a generally more uniform and characterized environment than is possible with their neutral atom counterparts
Summary
Optical frequency standards offer the possibility of making a step improvement of more than two orders of magnitude in the stability and accuracy of the realization of the SI second. Improvements in laser technology and high-finesse Fabry–Perot cavities have allowed the development of ultrastable laser systems with frequency instabilities below 1 × 10−15 at averaging times from 1 to 30 s [1, 2] These lasers can be used to interrogate highly forbidden optical reference transitions with the resulting quality factors approaching 1015. Ytterbium is unique among the ions being investigated as optical frequency standards in that its lowest-lying excited state is 2F7/2 (see figure 1) Once populated, this state can only decay to the ground state via electric octupole (E3) radiation at 467 nm with a natural lifetime of about 6 years [16]. The total relative standard uncertainty, including both systematic and statistical contributions, is evaluated to be 1.0 × 10−15, representing an improvement of a factor of 20 on the previously published value for this transition [8]
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