2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/108025The novel experimental realization of four-level optical quantum systems (ququarts) is presented. We exploit the polarization properties of frequency non-degenerate biphoton field to obtain such systems. A simple method that does not rely on interferometer is used to generate and measure the sequence of states that can be used in quantum key distribution (QKD) protocol.4 pages, 3 figuresQuantum Physicstext