  We propose a one-step scheme to generate GHZ states for superconducting flux
qubits or charge qubits in a circuit QED setup. The GHZ state can be produced
within the coherence time of the multi-qubit system. Our scheme is independent
of the initial state of the transmission line resonator and works in the
presence of higher harmonic modes. Our analysis also shows that the scheme is
robust to various operation errors and environmental noise.
