2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/139960We propose a quantum key distribution scheme which closely matches the performance of a perfect single photon source. It nearly attains the physical upper bound in terms of key generation rate and maximally achievable distance. Our scheme relies on a practical setup based on a parametric downconversion source and present-day, non-ideal photon-number detection. Arbitrary experimental imperfections which lead to bit errors are included. We select decoy states by classical post-processing. This allows to improve the effective signal statistics and achievable distance.4 pages, 3 figures. State preparation correctedQuantum Physicstext