Determination of Sr properties for a high-accuracy optical clock

We have carried out calculations towards the goal of reducing the inaccuracy of the Sr optical atomic clock to 1×10^-17 and below. In particular, we focused on ac polarizabilities of the 5s² ¹S₀ and $5s5p$ ³P₀ᵒ clock states that are important for reducing the uncertainty of black-body radiation-induced frequency shifts for the ¹S₀-³P₀ᵒ clock transition. Four low-lying even-parity states have been identified, whose total contribution to the static polarizability of the ³P₀ᵒ clock state is at the level of 90%. We show that if the contribution of these states is experimentally known with 0.1% accuracy, the same accuracy can be achieved for the total polarizability of the ³P₀ᵒ state. The corresponding uncertainty for the blackbody shift at a fixed room temperature will be below 1×10^-17. The calculations are confirmed by a number of experimental measurements on various Sr properties.