  We analyze the influence of errors on the implementation of the quantum
Fourier transformation (QFT) on the Ising quantum computer (IQC). Two kinds of
errors are studied: (i) due to spurious transitions caused by pulses and (ii)
due to external perturbation. The scaling of errors with system parameters and
number of qubits is explained. We use two different procedures to fight each of
them. To suppress spurious transitions we use correcting pulses (generalized
$2\pi k$ method) while to suppress errors due to external perturbation we use
an improved QFT algorithm. As a result, the fidelity of quantum computation is
increased by several orders of magnitude and is thus stable in a much wider
range of physical parameters.
