Realization of Four-Level Qudits Using Biphotons
Ekaterina Moreva, Gleb Maslennikov, Stanislav S. Straupe, S. P. Kulik · Physical Review Letters · 2006
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.