  We study numerically the dynamics of two-qubit gates with superconducting
charge qubits. The exact ratio of $E_J$ to $E_L$ and the corresponding
operation time are calculated in order to implement two-qubit gates. We
investigate the effect of finite rise/fall times of pulses in realization of
two-qubit gates. It is found that the error in implementing two-qubit gates
grows quadratically in rise/fall times of pulses.
