Engineering of multi-dimensional entangled states of photon pairs using   hyper-entanglement
  Multi-dimensional entangled states have been proven to be more powerful in some quantum information process. In this paper, down-converted photons from spontaneous parametric down conversion(SPDC) are used to engineer multi-dimensional entangled states. A kind of multi-degree multi-dimensional Greenberger-Horne-Zeilinger(GHZ) state can also be generated. The hyper-entangled photons, which are entangled in energy-time, polarization and orbital angular momentum (OAM), is proved to be useful to increase the dimension of systems and investigate higher-dimensional entangled states. 
Xi-Feng Ren, Guo-Ping Guo, Jian Li, Chuan-Feng Li and Guang-Can Guo