Absolute frequency measurement of the 1S0 - 3P0 transition of 171Yb

We report the absolute frequency measurement of the unperturbed transition S-1(0) - P-3(0) at 578 nm in Yb-171 realized in an optical lattice frequency standard relative to a cryogenic caesium fountain. The measurement result is 518 295 836 590 863.59(31) Hz with a relative standard uncertainty of 5.9x10(-16). This value is in agreement with the ytterbium frequency recommended as a secondary representation of the second in the International System of Units.