  We investigate electron-positron pair production in pulse-shaped electric
background fields using a non-Markovian quantum kinetic equation. We identify a
pulse-length range for subcritical fields still in the nonperturbative regime
where the number of produced pairs significantly exceeds that of a naive
expectation based on the Schwinger formula. From a conceptual viewpoint, we
find a remarkable quantitative agreement between the (real-time) quantum
kinetic approach and the (imaginary-time) effective action approach.
