Improved frequency ratio measurement with ⁸⁷Sr and ¹⁷¹Yb optical lattice clocks at NMIJ

We report improved frequency ratio measurement with $^{87}$Sr and $^{171}$Yb optical lattice clocks at the National Metrology Institute of Japan (NMIJ). The clock is enhanced several major modifications re-evaluated a reduced uncertainty $1.1\times10^{-16}$. employed an $4\times10^{-16}$ that was developed for contributing to International Atomic Time (TAI). result $\nu_{\mathrm{Yb}}/\nu_{\mathrm{Sr}}$ = 1.207 507 039 343 338 58(49)$_{\mathrm{sys}}$(6)$_{\mathrm{stat}}$ fractional $4.1\times10^{-16}$, which 3.4 times smaller than our previous result.