  The interaction between gravitational and electromagnetic waves in the
presence of a static magnetic field is studied. The field strength of the
static field is allowed to surpass the Schwinger critical field, such that the
quantum electrodynamical (QED) effects of vacuum polarization and magnetization
are significant. Equations governing the interaction are derived and analyzed.
It turns out that the energy conversion from gravitational to electromagnetic
waves can be significantly altered due to the QED effects. The consequences of
our results are discussed.
