The exact propagators of two one-dimensional systems with time-dependent
external fields are presented by following the path-integral method. It is
shown that the Bloch acceleration theorem can be generalized to the
impulse-momentum theorem in quantum version. We demonstrate that an evolved
Gaussian wave packet always keeps its shape in an arbitrary time-dependent
homogeneous driven field. Moreover, that stopping and accelerating of a wave
packet can be achieved by the pulsed field in a diabatic way.Comment: 8 pages, 6 figure