Two-photon spin states and entanglement states
  In this paper, we have given the spin states of two-photon, which are expressed by the quadratic combination of two single photon spin states, they are a kind of quantum expression. Otherwise, we give all entanglement states of two-photon, which are different from the xanzsd classical polarization vector expression of two-photon entanglement state. 
Xiao-Jing Liu, Xiang-Yao Wu, Jing-Bin Lu, Si-Qi Zhang, Hong-Li, Ji Ma,   Hong-Chun Yuan, Heng-Mei Li, Hai-Xin Gao and Jing-Wu Li
quant-ph