  Hybrid entangled states exhibit entanglement between different degrees of
freedom of a particle pair and thus could be useful for asymmetric optical
quantum network where the communication channels are characterized by different
properties. We report the first experimental realization of hybrid
polarization-orbital angular momentum (OAM) entangled states by adopting a
spontaneous parametric down conversion source of polarization entangled states
and a polarization-OAM transferrer. The generated quantum states have been
characterized through quantum state tomography. Finally, the violation of
Bell's inequalities with the hybrid two photon system has been observed.
