title: Highly efficient hyperentanglement concentration with two steps assisted by quantum swap gates.
abstract: We present a two-step hyperentanglement concentration protocol (hyper-ECP) for polarization-spatial hyperentangled Bell states based on the high-capacity character of hyperentanglement resorting to the swap gates, which is used to obtain maximally hyperentangled states from partially hyperentangled pure states in long-distance quantum communication. The swap gate, which is constructed with the giant optical circular birefringence (GOCB) of a diamond nitrogen-vacancy (NV) center embedded in a photonic crystal cavity, can be used to transfer the information in one degree of freedom (DOF) between photon systems. By transferring the useful information between hyperentangled photon pairs, more photon pairs in maximally hyperentangled state can be obtained in our hyper-ECP, and the success probability of the hyper-ECP is greatly improved. Moreover, we show that the high-fidelity quantum gate operations can be achieved by mapping the infidelities to heralded losses even in the weak coupling regime.
authors.affiliation: State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China.|Tsinghua National Laboratory for Information Science and Technology, Beijing 100084, China.|Collaborative Innovation Center of Quantum Matter, Beijing 100084, P. R. China.
authors.forename: Bao-Cang
authors.initials: BC
authors.lastname: Ren
authors.affiliation: State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China.|Tsinghua National Laboratory for Information Science and Technology, Beijing 100084, China.|Collaborative Innovation Center of Quantum Matter, Beijing 100084, P. R. China.
authors.forename: Gui Lu
authors.initials: GL
authors.lastname: Long