Vacuum birefringence

• Applicants: Dr. Felix Karbstein; Professor Dr. Hartmut Ruhl
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 392856280

Quantum electrodynamics (QED) predicts the quantum vacuum to mediate effective interactions between electromagnetic fields, resulting in violations of the classical superposition principle. This gives rise to a birefringence phenomenon for probe light traversing an electromagnetic field: if originally linearly polarized light is sent through a strong-field region, some of its photons can be scattered into a perpendicularly polarized mode, thereby effectively supplementing it with a small ellipticity. In inhomogeneous electromagnetic fields this phenomenon is generically accompanied by a diffraction effect constituting an additional signature of quantum vacuum nonlinearity in experiment.In the 1st funding period of this research unit we have demonstrated that both of these signatures are very sensitive to the details of the employed driving laser field profiles.In the 2nd funding period we aim at going beyond the simplified description of the driving laser fields as fundamental Gaussian beams and study vacuum birefringence and diffraction in the collision of XFEL and high-intensity laser pulses at unprecedented accuracy. Aside from these research activities of immediate relevance for experiment, we will pursue non-perturbative calculations at the basis of external-field QED.

• DFG Programme: Research Units
• Subproject of: FOR 2783: Probing the Quantum Vacuum at the High-Intensity Frontier
• International Connection: Russia
• Cooperation Partner: Professorin Dr. Elena Mosman