Measurement of the concurrence of arbitrary two-photon six-qubit hyperentangled state

Hyperentanglement is the quantum system entangled in several degrees of freedom (DOFs), which has attracted extensive attention in quantum communication. In the practical application of hyperentanglement, the key step is to know the information of the hyperentanglement. In this paper, we propose an efficient protocol to measure the concurrence of arbitrary two-photon six-qubit hyperentangled state, which simultaneously entangles in the polarization and double longitudinal momentum DOFs. This protocol requires the weak cross-Kerr nonlinearity and some linear optical elements to construct the quantum nondemolition detection gate. The concurrence in each DOF can be converted into the success probability of distilling some specified states. Our protocol may play an important role in future quantum information processing. Copyright (C) EPLA, 2020