Proposed Laboratory Tests of Time-Variation of the Fundamental Constants using the Ensemble of Frequency Standards at NPL

Limits to time variation of fundamental constants from comparisons of atomic frequency standards

“…This transition was first observed at NPL in the 172 Yb + ion [88]. In the 171 Yb + ion it has a natural lifetime of about 6 years [89]. The 4f 14 6s 2 S 1/2 (F = 0) − 4f 13 6s 2 2 F 7/2 (F = 3, M F = 0) hyperfine component is being developed as a frequency standard at NPL [70,90].…”

“…Standards based on clouds of ions held in electrodynamic quadrupole traps have been developed in 199 Hg + at NIST [47] and in 171 Yb + at NML (now National Measurement Institute, Australia) [46]. Although these standards demonstrated competitive stability and uncertainty a decade ago, the superior performance expected from optical frequency standards using these ions has led to their relative neglect.…”

“…The ytterbium ion has several transitions that can be used as frequency standards. The 6s 2 S 1/2 (F = 0) − 5d 2 D 3/2 (F = 2, M F = 0) hyperfine component of the E2 transition in 171 Yb + at 435 nm forms the basis of an optical frequency standard at PTB [69,85]. The 2 D 3/2 state has a natural lifetime of 51 ms [86], whereas the 2 D 5/2 state has a lifetime of 7.2 ms [87].…”

“…The quadrupole transitions in 88 Sr + , 171 Yb + and 199 Hg + are the basis of the most highly developed optical frequency standards and, along with the strontium atom transition discussed below, are the only optical frequency transitions to date which have been recommended as secondary representations of the SI second [52,91].…”

“…Trapped ion microwave standards have also been developed based on the even-Z odd isotopes 171 Yb + [46] and 199 Hg + [47], for which g I is proportional to the neutron g-factor (g n ). The Schmidt model does not reproduce the experimental values well for heavier elements but, as discussed in section 6, can be used to interpret limits to the rate of change of hyperfine transition frequencies.…”