  We introduce an approach to quantum cloning based on spin networks and we
demonstrate that phase covariant cloning can be realized using no external
control but only with a proper design of the Hamiltonian of the system. In the
1 -> 2 cloning we find that the XY model saturates the value for the fidelity
of the optimal cloner and gives values comparable to it in the genera N -> M
case. We finally discuss the effect of external noise. Our protocol is much
more robust to decoherence than a conventional procedure based on quantum
gates.
