Increasing Shannon dimensionality by hyperentanglement of spin and fractional orbital angular momentum.

We propose a single-photon spin-orbit entangled state analyzer for investigating the effective dimensionality of the Hilbert space spanned by spin and orbital angular momentum (OAM) states of twin photons from a spontaneous parametric downconversion (SPDC). The Pancharatnam-Berry phase element, the key element called a q plate equipped in the analyzer, induces the coupling between spin and OAM. It is found that the Shannon dimensionality of quantum channels in SPDC can be evidently increased owing to the spin-orbit hyperentanglement.