  Based on the obtained exact results we systematically study the quench
dynamics of a one-dimensional spin-1/2 transverse field Ising model with zero-
and finite-temperature initial states. We focus on the magnetization of the
system after a sudden change of the external field and a coherent
time-evolution process. With a zero-temperature initial state, the quench
magnetic susceptibility as a function of the initial field strength exhibits
strongly similar scaling behaviors to those of the static magnetic
susceptibility, and the quench magnetic susceptibility as a function of the
final field strength shows a discontinuity at the quantum critical point. This
discontinuity remains robust and always occurs at the quantum critical point
even for the case of finite-temperature initial systems, which indicates a
great advantage of employing quench dynamics to study quantum phase
transitions.
