SI-traceable measurement of an optical frequency at the low 10^−16 level without a local primary standard

Abstract

SI-traceable measurements of optical frequencies using International Atomic Time (TAI) do not require a local primary frequency reference, but suffer from an uncertainty in tracing to the SI second. For the measurement of the ⁸⁷Sr lattice clock transition, we have reduced this uncertainty to the low 10^-16 level by averaging three sets of ten-day intermittent measurements, in which we operated the lattice clock for 10⁴ s on each day. Moreover, a combined oscillator of two hydrogen masers was employed as a local flywheel oscillator (LFO) in order to mitigate the impact of sporadic excursion of LFO frequency. The resultant absolute frequency with fractional uncertainty of 4.3 × 10^-16 agrees with other measurements based on local state-of-the-art cesium fountains.

Advanced Satellite-Based Frequency Transfer at the 10−16 Level

“…We achieved a total uncertainty of 5.8 × 10 −16 . Thus, the consistency of the previous absolute frequencies reported by NICT and KRISS [10,11] was confirmed by y Yb /y Sr − 1 = (4.9 ± 5.8) × 10 −16 . We concluded the frequency ratio, R, as R = ν Yb /ν Sr = 1.207, 507, 039, 343, 337, 86(70).…”

“…These signals were provided to the earth stations for TWCP. By obtaining fractional frequencies y Yb and y Sr against each result of previous absolute frequency measurements f Yb and f Sr [11,10] on the basis of f UTC(KRIS) and f HM(NICT) , the frequency ratio of the two optical clock transitions ν Yb /ν Sr is measured as…”

Frequency measurement of the clock transition of an indium ion sympathetically-cooled in a linear trap

“…In session C, f comb was phase-locked to the clock laser of the Sr optical lattice clock (f Sr ), and the beat frequency between the 946nm clock laser and the nearest comb component was recorded by a conventional frequency counter (Agilent 53132A). The absolute frequency of the Sr lattice clock was recently evaluated with fractional uncertainty of 9.5 × 10 −16 [28,29]. In session A, B z was swept from -14 µT to 14 µT in order to confirm that the transitions of proper Zeeman sublevels were excited, and to evaluate the uncertainty of the residual 1st order Zeeman shift.…”

Towards the optical second: verifying optical clocks at the SI limit

“…*ssr+ah*sah+rb*srb+sensm 120))+dmu*(x-58305)/365.225)+sensq 0))+dq*(x-58305)/365.225)+sensalph* 120))+dalph*(xA summary of this work, as well as six other Yb absolute frequency measurements (yellow)[18,[27][28][29][30][31], and seventeen Sr measurements (red)[9,10,[34][35][36][37][38][39][40][41][42][43][44][45][46][47][48].Sr measurements are multiplied by the Yb/Sr ratio and the error bars are expanded as descibed in the main text. The fit function (orange) constrains possible variation of the Yb/Cs ratio, and the shaded region represents the 1σ uncertainty of the fit.…”

“…measurements[18,[27][28][29][30][31], ν avg Yb = 518 295 836 590 863.714(98) Hz. For the Sr frequency, we likewise determine a weighted average of 17 previous measurements[9,10,[34][35][36][37][38][39][40][41][42][43][44][45][46][47][48], ν avg Sr = 429 228 004 229 873.055(58) Hz. The frequency ratio derived from absolute frequency measurements is therefore, R avg abs = ν avg Yb /ν avg Sr = 1.207 507 039 343 337 86…”