Implementing W States and an Ancilla-Free 1→M Phase-Covariant Cloning via Adiabatic Evolution

A scheme is proposed for generating maximally multi-atom W states and realizing an ancilla-free 1→M phase-covariant quantum cloning. Compared to the previous scheme, our scheme is based on performing an adiabatic evolution through three separated cavities which remain in their respective vacuum states during the whole operation, the process is much more simple, and operations are reduced relatively. During the process of cloning, our scheme is not necessary to perform a measurement on atoms. And our scheme is robust for atomic spontaneous emission, cavity decay and photon leakage out of the fiber. All these convenient places make our scheme more feasible.