2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/94207We provide a justification of the quantum speed-up based on the complementary roles played by the reversible preparation of an entangled state before measurement and by the final measurement action.22 pages, RevTex, 1 PostScript file with figures. Some comments might indicate ineffective communication of the former version. The description of the mechanism of the quantum speed-up should now be clearer. An Overview of a few pages has been providedQuantum Physicstext