  We consider the process of electron-positron pair production in the presence
of strong electric backgrounds being rapidly switched on and off and examine
the total particle yield. For sufficiently sharp field profiles, the particle
number can be substantially enhanced. It is demonstrated that this enhancement
is quite similar to the phenomenon of dynamical assistance by a weak
high-frequency field superimposed on a strong background. Both these mechanisms
are analyzed by means of exact numerical computations, worldline instanton
approach, and the locally-constant field approximation. We identify the time
scale of the switching profile leading to the pair-production enhancement and
argue that the particle yield is highly unlikely to be increased by shaping the
switch off of realistic laser pulses. On the other hand, we confirm that it is
feasible to observe the dynamically assisted Schwinger effect by adding a
rapidly oscillating field to a strong electric background.
