Scalable Generation and Characterization of a Four-Photon Twelve-Qubit   Hyperentangled State
  An experimentally feasible scheme for generating a 12-qubit hyperentangled state via four photons, entangled in polarization, frequency and spatial mode, is proposed. We study the nature of quantum non-locality of this hyperentangled state by evaluating its violation degree to a Bell-type inequality, and find that the result agrees well with quantum mechanics prediction while extremely contradicts to the local realism constraint. 
Kun Du and Cong-Feng Qiao
quant-ph hep-ph