Experimental demonstration of fractional orbital angular momentum   entanglement of two photons
  The singular nature of a non-integer spiral phase plate allows easy manipulation of spatial degrees of freedom of photon states. Using two such devices, we have observed very high dimensional (D > 3700) spatial entanglement of twin photons generated by spontaneous parametric down-conversion. 
S.S.R. Oemrawsingh, X. Ma, D. Voigt, A. Aiello, E.R. Eliel, G.W. 't   Hooft, and J.P. Woerdman