Fig. 1. Energy level scheme of the Sr88 atom.

Fig. 2. Experimental setup. PMT: photomultiplier tube. EMCCD: electron multiplying charge-coupled device. OFC: optical frequency comb.

Fig. 3. Time sequence of the experiment for the 698 nm clock transition.

Fig. 4. Picture of the optical lattice-loaded atoms.

Fig. 5. Lifetime of the atoms in the 1D optical lattice.

Fig. 6. Clock transition spectrum. The black curve with the resolved sideband is the clock transition’s wide spectrum swept by a 1 kHz step size. The inset shows the narrow spectrum of the transition with a FWHM of 180 Hz; the solid red curve is a Lorentzian fit to the data yields.

Fig. 7. Measurement of the Rabi oscillation. The data are fitted with the function a(1−cos(2πΩFITΔt)exp(Δt/τFIT)) from Ref. [37], where ΩFIT is the actual atomic Rabi frequency and τFIT gives the decoherent time scale.