  The common tunneling picture of electron-positron pair creation in a strong
electric field is generalized to pair creation in combined crossed electric and
magnetic fields. This enhanced picture, being symmetric for electrons and
positrons, is formulated in a gauge-invariant and Lorentz-invariant manner for
quasistatic fields. It may be used to infer qualitative features of the pair
creation process. In particular, it allows for an intuitive interpretation of
how the presence of a magnetic field modifies and, in particular cases, even
enhances pair creation. The creation of electrons and positrons from the vacuum
may be assisted by an energetic photon, which can also be incorporated into
this picture of pair creation.
