  We investigate the use of ground-based gravitational-wave interferometers for
studies of the strong-field domain of QED. Interferometric measurements of
phase velocity shifts induced by quantum fluctuations in magnetic fields can
become a sensitive probe for nonlinear self-interactions among macroscopic
electromagnetic fields. We identify pulsed magnets as a suitable strong-field
source, since their pulse frequency can be matched perfectly with the domain of
highest sensitivity of gravitational-wave interferometers. If these
interferometers reach their future sensitivity goals, not only strong-field QED
phenomena can be discovered but also further parameter space of hypothetical
hidden-sector particles will be accessible.
