We discuss transformation and measurement of arbitrary four-level optical quantum systems, based on biphotons. A simple scheme preparation of twelve basis states serving for quantum key distribution protocol is suggested as well.
© 2006 Optical Society of America
(190.0190) Nonlinear optics : Nonlinear optics
(190.4410) Nonlinear optics : Nonlinear optics, parametric processes
(270.0270) Quantum optics : Quantum optics
(270.5290) Quantum optics : Photon statistics
S. Pavlovich Kulik, E. V. Moreva, and S. Straupe, "Ququarts Based on Biphotons," in Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference and Photonic Applications Systems Technologies, Technical Digest (CD) (Optical Society of America, 2006), paper JTuD90.
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