  Electron-positron pair production in strong electric fields, i.e., the
Sauter-Schwinger effect, is studied using the real-time Dirac-Heisenberg-Wigner
formalism. Hereby, the electric field is modeled to be a homogeneous,
single-pulse field with subcritical peak field strength. Momentum spectra are
calculated for four different polarizations - linear, elliptic, near-circular
elliptic or circular - as well as a number of linear frequency chirps. With
details depending on the chosen polarization the frequency chirps lead to
strong interference effects and thus quite substantial changes in the momentum
spectra. The resulting produced pairs' number densities depend non-linearly on
the parameter characterizing the polarization and are very sensitive to
variations of the chirp parameter. For some of the investigated frequency
chirps this can provide an enhancement of the number density by three to four
orders of magnitude.
