Transient response of a quantum wave to an instantaneous potential step   switching
  The transient response of a stationary state of a quantum particle in a step potential to an instantaneous change in the step height (a simplified model for a sudden bias switch in an electronic semiconductor device) is solved exactly by means of a semianalytical expression. The characteristic times for the transient process up to the new stationary state are identified. A comparison is made between the exact results and an approximate method. 
F. Delgado, H. Cruz, J.G. Muga