Using advanced computational modelling, a research team led by the University of Oxford, working in partnership with the Instituto Superior Técnico in the University of Lisbon, has achieved the first-ever real-time, three-dimensional simulations of how intense laser beams alter the 'quantum vacuum' -- a state once assumed to be empty, but which quantum physics predicts is full of virtual electron-positron pairs.

Excitingly, these simulations recreate a bizarre phenomenon predicted by quantum physics, known asvacuum four-wave mixing. This states that the combined electromagnetic field of three focused laser pulses can polarise the virtual electron-positron pairs of a vacuum, causing photons to bounce off each other like billiard balls - generating a fourth laser beam in a 'light from darkness' process. These events could act as a probe of new physics at extremely high intensities.

"This is not just an academic curiosity -- it is a major step toward experimental confirmation of quantum effects that until now have been mostly theoretical," said study co-author Professor Peter Norreys, Department of Physics, University of Oxford.

The work arrives just in time as a new generation of ultra-powerful lasers starts to come online. Facilities such as the UK's Vulcan 20-20, the European 'Extreme Light Infrastructure (ELI)' project, and China's Station for Extreme Light (SEL) and SHINE facilities are set to deliver power levels high enough to potentially confirm photon-photon scattering in the lab for the first time. Photon-photon scattering has already been selected as one of three flag-ship experiments at the University of Rochester's OPAL dual-beam 25 PW laser facility in the United States.

The simulations were carried out using an advanced version of OSIRIS, a simulation software package which models interactions between laser beams and matter or plasma.

Lead author Zixin (Lily) Zhang, a doctoral student at Oxford's Department of Physics, said: "Our computer program gives us a time-resolved, 3D window into quantum vacuum interactions that were previously out of reach. By applying our model to a three-beam scattering experiment, we were able to capture the full range of quantum signatures, along with detailed insights into the interaction region and key time scales. Having thoroughly benchmarked the simulation, we can now turn our attention to more complex and exploratory scenarios -- including exotic laser beam structures and flying-focus pulses."

Crucially, these models provide details that experimentalists depend on to design precise, real-world tests including realistic laser shapes and pulse timings. The simulations also reveal new insights, including how these interactions evolve in real time and how subtle asymmetries in beam geometry can shift the outcome.

According to the team, the tool will not only assist in planning future high-energy laser experiments but could also help search for signs of hypothetical particles such as axions and millicharged particles -- potential candidates for dark matter.

Study co-author Professor Luis Silva (at the Instituto Superior Tecnico, University of Lisbon and Visiting Professor in Physics at the University of Oxford) added: "A wide range of planned experiments at the most advanced laser facilities will be greatly assisted by our new computational method implemented in OSIRIS. The combination of ultra-intense lasers, state-of-the-art detection, cutting-edge analytical and numerical modelling are the foundations for a new era in laser-matter interactions, which will open new horizons for fundamental physics."

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