Scheme for the implementation of optimal cloning of two pairs of   orthogonal states
  We propose a feasible scheme to implement the 1-to-2 optimal cloning transformation for two pairs of orthogonal states of two-dimensional quantum systems in the context of cavity QED. The copied qubits are shown to be inseparable by using Peres-Horodecki criterion. 
Zhuo-Liang Cao, Wei Song