A proposal for realizing a 3-qubit controlled-phase gate with   superconducting qubit systems coupled to a cavity
  We present a way to realize a 3-qubit quantum controlled-phase gate with superconducting qubit systems coupled to a cavity. This proposal does not require adjustment of the qubit level spacings or identical qubit-cavity coupling constants. Moreover, since only a resonant interaction is applied, the gate can be performed fast, within $\sim $ 10 nanosecond. This proposal is quite general, which can be applied to various types of superconducting qubits, atoms trapped in a cavity, or quantum dots coupled to a resonator. 
Chui-Ping Yang
quant-ph cond-mat.supr-con