  It has been recently pointed out [V. Giovanetti, S. Lloyd, and L. Maccone,
Europhys. Lett., {\bf 62} pp. 615-621 (2003)] that, for certain classes of
states, quantum entanglement enhances the "speed" of evolution of composite
quantum systems, as measured by the time a given initial state requires to
evolve to an orthogonal state. We provide here a systematic study of this
effect for pure states of bipartite systems of low dimensionality, considering
both distinguishable (two-qubits) subsystems, and systems constituted of two
indistinguishable particles.
