Entangling a Series of Trapped Ions by Moving Cavity Bus

Entangling multiple qubits is one of the central tasks of quantum information processing. We propose an approach to entangle a number of cold ions (individually trapped in a string of microtraps) by a moved cavity. The cavity is pushed to include the ions one by one with a uniform velocity and thus the information stored in former ions could be transferred to the latter ones by such a moving cavity bus. Since the positions of the trapped ions are precisely located, the strengths and durations of the ion-cavity interactions can be exactly controlled. As a consequence, by properly setting the relevant parameters, typical multi-ion entangled states, e.g., W state for 10 ions, could be deterministically generated. The feasibility of the proposal is also discussed.