High Accuracy Correction of Blackbody Radiation Shift in an Optical Lattice Clock

We have determined the frequency shift that blackbody radiation is inducing on the 5s² ¹S₀--5s5p ³P₀ clock transition in strontium. Previously its uncertainty limited the uncertainty of strontium lattice clocks to 1×10^-16. Now the uncertainty associated with the blackbody radiation shift correction translates to a 5×10^-18 relative frequency uncertainty at room temperature. Our evaluation is based on a measurement of the differential dc polarizability of the two clock states and on a modeling of the dynamic contribution using this value and experimental data for other atomic properties.