Studies of Yb $^{1}$S$_{0}$ -- $^3$P$_0$ clock transitions

We are exploring two quite different methods for observing the ultra-sharp $6s^2$ $^{1}$S$_{0}$ -- $6s6p$ $^3$P$_0$ optical interval in atomic Yb, which is considered a primary candidate for future optical frequency standards [1].In the first method, we observe the 578 nm single photon transition allowed in the odd isotopes through internal hyperfine coupling of the nuclear spin.† We shine a 578 nm laser beam on cold Yb atoms held in a magneto-optical trap (MOT), and detect a decrease in MOT fluorescence when the laser is resonant with the clock transition.† Our second approach is to use the even Yb isotopes, connecting the $^{1}$S$_{0}$ and $^3$P$_0$ states† by† a multi- photon transition [2]. Sharp electromagnetically induced transparency and absorption (EITA) resonance features appear when the photon frequencies combine to equal† the $^{1}$S$_{0}$ -- $^3$P$_0$ clock interval.† We will describe our initial studies of† 2 and 3 photon resonances in Yb, including Doppler-free 3 photon EITA. [1]S. G.† Porsev, A. Derevianko, E. N. Fortson, Phys. Rev. A {\bf 69}, 021403(R)† (2004); H. Katori, in {\it Proc. 6th Symposium Frequency Standards and Metrology}, edited by P. Gill (World Scienti.c, Singapore, 2002), pp. 323-330 [2]Tao Hong, Claire Cramer, Warren Nagourney, E. N. Fortson, physics/0409051 and to be published in Phys. Rev. Lett.; Robin Santra, Ennio Arimondo, Tetsuya Ido, Crhis H. Greene, Jun Ye, physics/0411197