Qutrit state engineering with biphotons
  The novel experimental realization of three-level optical quantum systems is presented. We use the polarization state of biphotons to generate a specific sequence of states that are used in the extended version of BB84 protocol. We experimentally verify the orthogonality of the basis states and demonstrate the ability to easily switch between them. The tomography procedure is employed to reconstruct the density matrices of generated states. 
Yu. Bogdanov, M. Chekhova, S. Kulik, G. Maslennikov, C.H. Oh, M.K.   Tey, A. Zhukov