Preservation of entanglement in a two-qubit-spin coupled system
  A theoretical scheme to preserve the entanglement in a two-qubit-spin coupled system in the presence of Dzyaloshinskii-Moriya (DM) anisotropic antisymmetric interaction is proposed. Based on a sequence of operations performed periodically on the system, the scheme can preserve the entanglement of the system starting from any initial state with any high precision for any long duration. 
Yu-Chen Hou, Guo-feng Zhang, Yan Chen, Heng Fan
quant-ph