Direct comparisons of European primary and secondary frequency standards via satellite techniques

Abstract

We carried out a 26-day comparison of five simultaneously operated optical clocks and six atomic fountain clocks located at INRIM, LNE-SYRTE, NPL and PTB by using two satellite-based frequency comparison techniques: broadband Two-Way Satellite Time and Frequency Transfer (TWSTFT) and Global Positioning System Precise Point Positioning (GPS PPP). With an enhanced statistical analysis procedure taking into account correlations and gaps in the measurement data, combined overall uncertainties in the range of 1.8 × 10 −16 to 3.5 × 10 −16 for the optical clock comparisons were found. The comparison of the fountain clocks yields results with a maximum relative frequency difference of 6.9 × 10 −16 , and combined overall uncertainties in the range of 4.8 × 10 −16 to 7.7 × 10 −16 .

Transportable Strontium Optical Lattice Clocks Operated Outside Laboratory at the Level of 10−18 Uncertainty

“…[ 8–16 ] Frequency dissemination by optical fibers or satellite transfer allows comparison of optical clocks between distant laboratories in Europe. [ 17,18 ] Since the gravitational redshift for 1‐cm height difference on the Earth corresponds to a fractional clock frequency shift of 10 −18 , such highly accurate clocks are expected to be used for geodetic applications. [ 19,20 ] So far, the‐state‐of‐the‐art clocks are demonstrated in well‐controlled laboratory environments.…”

Intercontinental comparison of optical atomic clocks through very long baseline interferometry

“…However, they have not reached a transoceanic scale 19 and therefore intercontinental comparisons are only possible by microwave satellite transfer techniques 20 . Among these are two-way time-and-frequency transfer, which makes use of geostationary telecommunication satellites 21,22 , or precise point positioning 23 , which relies on the constellation of the Global Positioning System (GPS). These techniques achieve a typical uncertainty at the level of 10 −15 at 1 d of averaging time that limits the comparison of optical clocks.…”

Measuring Height Difference Using Two-Way Satellite Time and Frequency Transfer

“…In 2016, an experiment using carriedphase TWSTFT was performed between the two stations of NICT (National Institute of Information and Communications Technology) and KRISS (Korea Research Institute of Standards and Science) with Sr and Yb OAC, and the instability for a frequency transfer at the 10 −16 level after 12 h was achieved [24]. Riedel et al (2020) conducted a 26-day comparison of five simultaneously operated OACs and six MACs located at SYRTE, NPL, INRIM, LNE, and PTB by using TWSTFT and GPSPPP. Considering the correlations and gaps of measurement data, they improved the statistical analysis procedure; combined overall uncertainties in the range of 1.8 × 10 −16 to 3.5 × 10 −16 for the OAC comparisons were found [25].…”

“…Riedel et al (2020) conducted a 26-day comparison of five simultaneously operated OACs and six MACs located at SYRTE, NPL, INRIM, LNE, and PTB by using TWSTFT and GPSPPP. Considering the correlations and gaps of measurement data, they improved the statistical analysis procedure; combined overall uncertainties in the range of 1.8 × 10 −16 to 3.5 × 10 −16 for the OAC comparisons were found [25]. To investigate the feasibility of transportable atomic clock comparison using TWSTFT, we conducted a MAC comparison experiment at the Beijing Institute of Radio Metrology and Measurement (BIRMM), Beijing [26,27].…”