Nonlinear Quantum Electrodynamics (QED)

Quantum Electrodynamics (QED) is the most precisely tested theory in history of science. However, only a few experimental studies of nonlinear QED exist so far. 

Testing this regime requires extreme conditions, which can be found for example in the magnetic field on the surface of a neutron star, in the interaction of extremely high-energetic cosmic particles or in the collision of heavy ions.

We intend to investigate NL-QED by studying (i) nonlinear Xray-matter interactions and (ii) the interaction of ultrahigh-intensity optical laser radiation with relativistic electron beams. In case (i), we investigate nonlinear Compton scattering using the focused radiation of an X-ray free-electron laser (more).
In case (ii) we investigate the interaction of extremely large electric fields where the presence of such a field can disturb the quantum vacuum and as a consequence lead to the generation of matter from vacuum. Here, the fluctuating virtual electron-positron particle pairs can become real. This can occur if the field is strong enough to separate the virtual electron from the positron before they are able to recombine. More specific, if the field reaches the so-called quantum critical strength (Schwinger field strength), where the voltage drop across the distance of a Compton wavelength is equal to the rest mass of an electron, which is given by E=1016 V/cm. Such fields can be achieved in the collision of an ultra-high intensity (optical) laser beam with an ultra-relativistic electron beam.