A robust scheme for implementing optimal economical phase-covariant quantum cloning with quantum-dot spins in optical microcavities

We present a scheme to implement an optimal symmetric 1→21→2 economical phase-covariant quantum cloning machine (EPCCM) with quantum dot (QD) spins in optical microcavities by using a photon as a data bus. The EPCCM copies deterministically the quantum states on southern or northern Bloch hemisphere from one QD spin to two with an optimal fidelity. By analyzing the fidelity of quantum cloning we confirm that it is robust against the dissipation caused by cavity decay, side leakage and dipole decay. For a strong coupling regime, the cloning fidelity approaches a stable optimal bound. Even in a weak coupling regime, it can also achieve a satisfactory high value close to the optimal bound.