  We investigated the coherence of spin-polarized ^{87}Sr atoms trapped in a
light-shift-free one-dimensional optical lattice during their interaction with
a clock laser on the ^1S_0-^3P_0 transition. Collapses and revivals appeared
for more than 50 Rabi cycles, attributed to the thermal distribution of
discrete vibrational states in the lattice potential. The population
oscillation in the clock states lasted more than 1s, demonstrating high
immunity from decoherence. This long atomic coherence suggests the feasibility
of Pauli blocking of collisions in optical clock excitation.
