  Ultracold atoms in optical lattices offer a great promise to generate
entangled states for scalable quantum information processing owing to the
inherited long coherence time and controllability over a large number of
particles. We report on the generation, manipulation and detection of atomic
spin entanglement in an optical superlattice. Employing a spin-dependent
superlattice, atomic spins in the left or right sites can be individually
addressed and coherently manipulated by microwave pulses with near unitary
fidelities. Spin entanglement of the two atoms in the double wells of the
superlattice is generated via dynamical evolution governed by spin
superexchange. By observing collisional atom loss with in-situ absorption
imaging we measure spin correlations of atoms inside the double wells and
obtain the lower boundary of entanglement fidelity as $0.79\pm0.06$, and the
violation of a Bell's inequality with $S=2.21\pm 0.08$. The above results
represent an essential step towards scalable quantum computation with ultracold
atoms in optical lattices.
