Quantum-State Engineering of Multiple Trapped Ions for Center-of-Mass   Mode
  We propose a scheme to generate a superposition with arbitrary coefficients on a line in phase space for the center-of-mass vibrational mode of N ions by means of isolating all other spectator vibrational modes from the center-of-mass mode. It can be viewed as the generation of previous methods for preparing motional states of one ion. For large number of ions, we need only one cyclic operatin to generate such a superposition of many coherent states. 
Hao-Sheng Zeng, Xi-Wen Zhu and Ke-Lin Gao