Quantum cloning based on iSWAP gate with nitrogen-vacancy centers in photonic crystal cavities

we propose a scheme for physical implementation for the optimal asymmetric (symmetric) 1→2 universal quantum cloning, the optimal symmetric economical 1→3 phase-covariant cloning and the optimal asymmetric (symmetric) real state cloning based on an iSWAP gate between separated nitrogen-vacancy (NV) centers embedded inphotonic crystal cavities. This two-qubit iSWAP gate is produced by the long-range interaction between two distributed NV centers mediated by the vacuum fields of the cavities. The analysis results show that our scheme is efficient and may be useful for scalable quantum information processing.