Preparation of arbitrary qutrit state based on biphotons
  The novel experimental realization of three-state optical quantum systems is presented. We use the polarization state of biphotons,propagating in single frequency- and spatial mode, to generate an arbitrary qutrits. In particular the specific sequence of states that are used in the extended version of BB84 quantum key distribution protocol was generated and tested. We experimentally verify the orthogonality of the 12 basic states and demonstrate the ability of switching between them. The tomography procedure is applied to reconstruct the density matrices of generated states. 
Yu.I.Bogdanov, M.V.Chekhova, S.P.Kulik, G.A.Maslennikov, C.H. Oh, M.K.   Tey