Photon-Photon Scattering
As already described by Heisenberg and Euler in 1935, “...even in situations where the [photon] energy is not sufficient for matter production, its virtual possibility will result in a ‘polarization of the vacuum’ and hence in an alteration of Maxwell’s equations.”
Heisenberg, W. & Euler, H. Folgerungen aus der diracschen Theorie des Positrons. Zeitschrift für Physik 98, 714–732 (1936).
Thus, the vacuum acts like a nonlinear optical medium and the photons can interact via the virtual particle-antiparticle pair, thereby changing their properties like direction or polarization state.
By colliding two (or more) high-intensity laser pulses at optical wavelengths, a signature of photons scattered off the “quantum vacuum” should be detectable. For currently available laser powers, the number of signal photons is expected to be very low (order of 1 to several 100 per shot) compared to the background of more than 10^20 photons in the driving laser pulses.
On the path towards a first discovery experiment demonstrating all-optical photon scattering in vacuum, both the theoretical ideal setup given concrete available laser parameters as well as many practical issues need to be addressed.
Together with the colleagues of the research unit, we are currently investigating possible setups and sensitive detection schemes to make such an experiment possible in the not-too-distant future.
Research coordinator: Prof. Jörg Schreiber