Efficient hyperentangled Greenberger–Horne–Zeilinger states analysis with cross-Kerr nonlinearity

The entangled states analysis is a very important element for quantum information. It is impossible to unambiguously distinguish the three-photon Greenberger–Horne–Zeilinger (GHZ) states in polarization, resorting to linear optical elements only. Here, we propose an efficient scheme to complete three-photon hyperentangled GHZ states analysis (HGSA) with the help of the cross-Kerr nonlinearity. The three-photon HGSA scheme can also be generalized to N-photon hyperentangled GHZ states analysis. We discuss the application of the HGSA in the quantum secure direct communication (QSDC) with polarization and spatial-mode degrees of freedom. The results show that the HGSA not only increase the channel capacity but also ensure the unconditional security in long-distance quantum communication.