The probability distributions of the walker in PS at the 4th step with the initial walker state |α = 3〉 and coin state , the step size Δθ = 0.3, and ɛ = 0.01 GHz in solid line and ɛ = 0.012 GHz in dashed line respectively. The phase distribution shows a ballistic behavior of the QW in PS. With the strength of the driving field increasing, the decoherence introduced by displacement in position space increases and the phase distribution tends to be the combination of those of QW and RW.