2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/113201We develop a strong and computationally simple entanglement criterion. The criterion is based on an elementary positive map Phi which operates on state spaces with even dimension N >= 4. It is shown that Phi detects many entangled states with positive partial transposition (PPT) and that it leads to a class of optimal entanglement witnesses. This implies that there are no other witnesses which can detect more entangled PPT states. The map Phi yields a systematic method for the explicit construction of high-dimensional manifolds of bound entangled states.4 pages, no figures, replaced by published version (minor changes), Journal-reference addedQuantum Physicstext