We observe the quantum coherent dynamics of atomic spinor wave packets in t
he double-well potentials of a far-off-resonance optical lattice. With appr
opriate initial conditions the system Rabi oscillates between the left and
right localized states of the ground doublet, and at certain times the wave
packet corresponds to a coherent superposition of these mesoscopically dis
tinct quantum states. The atom/optical double-well potential is a flexible
and powerful system for further study of quantum coherence, quantum control
, and the quantum/classical transition.