Absolute Frequency Measurement of the 40Ca+ 4s 2S1/2-3d 2D5/2 Clock Transition

We report on the first absolute transition frequency measurement at the 10(-15) level with a single, laser-cooled Ca-40(+) ion in a linear Paul trap. For this measurement, a frequency comb is referenced to the transportable Cs atomic fountain clock of LNE-SYRTE and is used to measure the Ca-40(+) 4s S-2(1/2)-3d D-2(5/2) electric-quadrupole transition frequency. After the correction of systematic shifts, the clock transition frequency nu(+)(Ca)=411 042 129 776 393.2(1.0) Hz is obtained, which corresponds to a fractional uncertainty within a factor of 3 of the Cs standard. In addition, we determine the Lande g factor of the 3d(2)D(5/2) level to be g(5/2)=1.200 334 0(3).