  We study the quantum operation of coupled superconducting flux qubits under a
microwave irradiation. The flux qubits can be described as magnetic dipole
moments in the limit of weak microwave field amplitude consistent with usual
experimental situations. With the Hamiltonian for coupled qubits under a
microwave field, we show that a strong coupling enables to realize the high
performance controlled-NOT gate operation. For practical quantum computing we
analyze the effect of microwave on switching function of phase-coupled qubits.
