Interferometry of light propagation in pulsed fields

– 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. Introduction. – Charged quantum fluctuations as predicted by quantum electrodynamics (QED) induce nonlinear self-interactions of electromagnetic fields [1]. This fundamental violation of the superposition principle of classical electrodynamics has not yet been observed on the level of macroscopic electromagnetic fields. Even though light-by-light interactions have been verified in experiments involving high-energy photons [2], an investigation of nonlinear interactions of macroscopic fields would probe QED and its vacuum structure in a large-amplitude regime which is comparatively little explored in quantum field theory. In fact, large-amplitude or strong-field experiments not only give access to unprecedented fundamental tests of QED, but also facilitate a search for hypothetical particles with light masses and weak couplings to photons (hidden-sector searches). This prospect has recently triggered a remarkable growth of experimental and theoretical activities concerned with strong-field and optical set-ups, for recent reviews see [3, 4]. A sensitive probe for vacuum nonlinearities is light propagation in strong electromagnetic fields. The lowest-order nonlinear modifications of Maxwell’s theory as induced by QED vacuum polarization are described by the (lowest-order) Heisenberg-Euler Lagrangian [1], L = 1 2 (E − B) + 2α 2 45m4 (E − B) + 7 2α 2