  An analogous model system for quantum information processing is discussed,
based on classical wave optics. The model system is applied to three examples
that involve three qubits: ({\em i}) three-particle Greenberger-Horne-Zeilinger
entanglement, ({\em ii}) quantum teleportation, and ({\em iii}) a simple
quantum error correction network. It is found that the model system can
successfully simulate most features of entanglement, but fails to simulate
quantum nonlocality. Investigations of how far the classical simulation can be
pushed show that {\em quantum nonlocality} is the essential ingredient of a
quantum computer, even more so than entanglement. The well known problem of
exponential resources required for a classical simulation of a quantum
computer, is also linked to the nonlocal nature of entanglement, rather than to
the nonfactorizability of the state vector.
