  We proposed an analytical model to analyze the Landau-Zener interference in a
multilevel superconducting flux qubit driven by large amplitude external
fields. Our analytical results agree remarkably with those of the experiment
[Nature 455, 51 (2008)]. Moreover, we studied the effect of driving-frequency
and dephasing rate on the interference. The dephasing generally destroys the
interference while increasing frequency rebuilds the interference at large
dephasing rate. At certain driving frequency and dephasing rate, the
interference shows some anomalous features as observed in recent experiments.
