Uncertainty Evaluation of an ¹⁷¹Yb Optical Lattice Clock at NMIJ

We report an uncertainty evaluation of an ¹⁷¹Yb optical lattice clock with a total fractional uncertainty of 3.6×10^-16 , which is mainly limited by the lattice-induced light shift and the blackbody radiation shift. Our evaluation of the lattice-induced light shift, the density shift, and the second-order Zeeman shift is based on an interleaved measurement where we measure the frequency shift using the alternating stabilization of a clock laser to the 6s^{2 1}S₀-6s6p ³P₀ clock transition with two different experimental parameters. In the present evaluation, the uncertainties of two sensitivity coefficients for the lattice-induced hyperpolarizability shift d incorporated in a widely used light shift model by RIKEN and the second-order Zeeman shift a_Z are improved compared with the uncertainties of previous coefficients. The hyperpolarizability coefficient d is determined by investigating the trap potential depth and the light shifts at the lattice frequencies near the two-photon transitions 6s6p³P₀-6s8p³P₀, 6s8p³P₂, and 6s5f³F₂. The obtained values are d=-1.1(4) μ Hz and a_Z=-6.6(3) Hz/mT². These improved coefficients should reduce the total systematic uncertainties of Yb lattice clocks at other institutes.