title: Realization of four-level qudits using biphotons.
abstract: The novel experimental realization of four-level optical quantum systems (ququarts) is presented. We exploit the polarization properties of the frequency nondegenerate biphoton field to obtain such systems. A simple method that does not rely on am interferometer is used to generate and measure the sequence of states that can be used in quantum key distribution protocol.
authors.affiliation: Moscow Engineering Physics Institute, State University, Russia. ekaterina.moreva@gmail.com
authors.forename: E V
authors.initials: EV
authors.lastname: Moreva
authors.forename: G A
authors.initials: GA
authors.lastname: Maslennikov
authors.forename: S S
authors.initials: SS
authors.lastname: Straupe
authors.forename: S P
authors.initials: SP
authors.lastname: Kulik