New experiment challenges the principles of quantum electrodynamics

The HZDR team proposes improvements to experiments aimed at probing the limits of physics.

Completely empty – that’s how most of us imagine a vacuum. But in reality, it is filled with flickers of energy, or quantum fluctuations. Scientists are now preparing laser experiments aimed at examining these vacuum fluctuations in new ways, which could provide clues to new laws of physics.

The Dresden-Rossendorf-Helmholtzzentrum (HZDR) research team has developed a series of suggestions designed to make experiments more effective and increase the chances of success.The research team will publish their findings in a scientific journal Physical Review D.

The world of physics has long recognized that the vacuum is not completely hollow, but filled with vacuum fluctuations, eerie quanta that flicker around in time and space. Although it cannot be captured directly, its effects can be observed indirectly, for example through changes in the electromagnetic field of small particles.

However, it is still not possible to verify vacuum fluctuations without the presence of particles. If this can be achieved, one of the fundamental theories of physics, quantum electrodynamics (QED), will be proven in a previously untested area. However, if such experiments reveal deviations from theory, it would suggest the existence of new, previously undiscovered particles.

Dr. Ulf Zastrau heads the HED (High Energy Density Science) experimental station at European XFEL. HED Beam In his chamber, flashes from his X-ray laser, the world’s largest, must be matched with light pulses from his ReLaX high-power laser operated by HZDR to detect vacuum fluctuations. Credit: European XFEL / Jan Hosan

Experiments to achieve this are planned as part of the Helmholtz International Extreme Field Beamline (HIBEF), a research consortium led by HZDR, at the HED experimental station of the world’s largest X-ray laser, the European XFEL, in Hamburg. There is. . The basic principle is that an ultra-powerful laser fires short, powerful flashes into a vacuumed stainless steel chamber. The aim is to manipulate vacuum fluctuations to, as if by magic, change the polarization of his X-ray flashes from his XFEL in Europe, i.e. rotate their direction of vibration.

“It’s like sliding a clear plastic ruler between two polarizing filters and bending it back and forth,” explains HZDR theorist Professor Ralf Schutzhold. “A filter is originally set up to prevent light from passing through it. Bending the ruler changes the direction of the vibrations of light, allowing you to see something.” In this analogy, the ruler responds to fluctuations in the vacuum. and a super powerful laser flash bends the vacuum fluctuations.

Two flashes instead of just one

The original concept involved firing a single optical laser flash into a chamber and using special measurement techniques to record whether the polarization of the X-ray flash changed. But there’s a problem. “The signal can be very weak,” Schutzhold explains. “Only one in a trillion X-ray photons can change its polarization.”

However, this may be below current measurement limits, and events may simply slip through the cracks undetected. Schutzhold and his team therefore rely on a variation of firing not just one but two of his light laser pulses into a vacuum chamber simultaneously.

Both flashes run into it and literally collide. Her X-ray pulses from Europe’s XFEL are set to hit precisely the point of impact. The clincher: Laser flash collisions affect her X-ray pulses like a kind of crystal. Just as X-rays are diffracted, or deflected, when they pass through natural crystals, XFEL X-ray pulses are deflected by the brief “crystal of light” of the two colliding laser flashes.

“This not only changes the polarization of the X-ray pulse, but also slightly deflects the pulse,” explains Ralf Schutzholt. The researchers hope that this combination may improve the chances of actually measuring effects. The researchers calculated different options for the firing angle of the two laser flashes colliding inside the chamber. Experimentation will tell you which variant works best.

Are you targeting ultralight ghost particles?

The visibility could also be further improved if the two laser flashes fired into the chamber were not the same color, but two different wavelengths. This also allows for small changes in the energy of the X-ray flash, which is useful for measuring effectiveness as well. “However, this is technically very difficult and may be implemented at a later date,” Schutzhold says.

The project is currently in the planning stage in collaboration with the European XFEL team at the HED experimental station in Hamburg, with first trials scheduled to begin in 2024. If successful, QED could be confirmed again.

However, perhaps experiments will reveal deviations from established theory. This could be caused by previously undiscovered particles, such as ultralight ghost particles known as axions. “And it will clearly demonstrate additional laws of nature that were previously unknown,” Schutzholt says.

Reference: “Quantum vacuum diffraction and birefringence detection scheme” N. Ahmadiniaz, TE Cowan, J. Grenzer, S. Franchino-Viñas, A. Laso Garcia, M. Šmíd, T. Toncian, MA Trejo, R. Schützhold , October 10, 2023 Physical Review D.
DOI: 10.1103/PhysRevD.108.076005