Simple scheme for preparing W states and cloning via adiabatic passage in ion-trap systems

We propose a simple protocol for the generation of W states and the implementation of phase-covariant cloning and anticloning machines via adiabatic passage in ion-trap system. In the present scheme, the system state evolves in the dark space during the whole procedure. We only use the two-level ions to act as memory and do not require the transfer quantum information from ions to the vibrational mode, which makes the system simple and robust against decoherence. Moreover, the proposal may be feasible based on current technologies.