Observation and absolute frequency measurements of the 1S0-3P0 optical clock transition in neutral ytterbium -: art. no. 083003

We report the direct excitation of the highly forbidden (6s(2))S-1(0)<->(6s6p)P-3(0) optical transition in two odd isotopes of neutral ytterbium. As the excitation laser frequency is scanned, absorption is detected by monitoring the depletion from an atomic cloud at similar to 70 mu K in a magneto-optical trap. The measured frequency in Yb-171 (F=1/2) is 518 295 836 591.6 +/- 4.4 kHz. The measured frequency in Yb-173 (F=5/2) is 518 294 576 847.6 +/- 4.4 kHz. Measurements are made with a femtosecond-laser frequency comb calibrated by the National Institute of Standards and Technology cesium fountain clock and represent nearly a 10(6)-fold reduction in uncertainty. The natural linewidth of these J=0 to J=0 transitions is calculated to be similar to 10 mHz, making them well suited to support a new generation of optical atomic clocks based on confinement in an optical lattice.