Simple and Scalable Method for Generation of Trapped Ions’ W State

By introducing auxiliary energy levels, we propose a simple and scalable method for generation of trapped ions’ W state. In our proposal, except the addressing phase shift operation for the first ion, all the other unitary operations (include typical carrier and sideband transitions) can be implemented using global laser beam, so the experimental difficulty can be largely reduced. Furthermore, the number of the laser pulses for W state generation is independent of the size of the W state, so our proposal is highly scalable. This method may be applied to generation of large-size entanglement of trapped ions in the near future.