  Entangling multiple qubits is one of the central tasks for quantum
information processings. Here, 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 an 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.
