Miniature Particle Accelerator Cracks Fermi’s 70-Year-Old Cosmic Ray Mystery

Physicists have recreated the mechanism behind cosmic ray acceleration in a lab for the first time using ultracold atoms and a device no bigger than a human hair.

Scientists have achieved a major breakthrough in particle physics by using ultracold atoms to demonstrate a new method of acceleration, offering new insight into the mysterious behavior of cosmic rays, according to a recent study.

For the first time, researchers have recreated a phenomenon known as the Fermi acceleration mechanics, —first proposed over 70 years ago, inside a laboratory. They accomplished this by making ultracold atoms collide with specially designed, movable potential barriers. This success marks a significant achievement in the study of high-energy astrophysics.

Fermi acceleration, introduced by physicist Enrico Fermi in 1949, is believed to explain how cosmic rays gain their extreme energies. The process also exhibits certain universal characteristics that have inspired several mathematical models, including the well-known Fermi-Ulam model. Despite decades of effort, scientists had not been able to construct a reliable version of this accelerator on Earth—until now.

In a paper published in Physical Review Letters, a team of researchers from the Universities of Birmingham and Chicago detail their success in creating a fully controllable Fermi accelerator. This experimental device allowed them to directly observe significant particle acceleration for the first time in a controlled setting.

Miniature Accelerator With Big Potential

The accelerator – just 100 micrometres in size – can quickly accelerate ultracold samples to velocities of more than half a meter per second. It does this, making movable optical potential barriers collide with trapped ultracold atoms.

By combining energy gain and particle losses, the scientists can also obtain energy spectra analogous to those observed in cosmic rays, providing the first direct verification of the so-called Bell’s result, which is at the core of every cosmic ray acceleration model.

Co-author Dr. Amita Deb, from the University of Birmingham, commented: “Results delivered by our Fermi accelerator surpass the best-in-class acceleration methods used in quantum technology. The technology has the additional advantages of featuring an exceptionally simple and miniaturised setup, and no theoretical upper limits.”

Toward Simulating the Universe in the Lab

The accelerator’s generation of ultracold atomic jets demonstrates the potential for high-precision control over particle acceleration. The ability to study Fermi acceleration with cold atoms opens new possibilities for investigating phenomena relevant to high-energy astrophysics.

Future areas of research include the study of particle acceleration at shocks, magnetic reconnection, and turbulence, which are critical processes in the universe. Studying quantum Fermi acceleration could lead to the development of new tools for manipulating quantum wavepackets, offering promising avenues for advancements in quantum information science.

Dr. Vera Guarrera, one of the leading authors from the University of Birmingham, commented: “Our work represents the first step towards the study of more complex astrophysical mechanisms in the lab. The simplicity and effectiveness of our Fermi accelerator make it a powerful tool for both fundamental research and practical applications in quantum technology.”

The research team plans to further explore the applications of their Fermi accelerator in various fields, including quantum chemistry and atomtronics. They aim to investigate how different kinds of interactions affect the acceleration rate and the maximum energy attainable, providing valuable insights for both theoretical and experimental physics.

Reference: “Observation of Fermi Acceleration with Cold Atoms” by G. Barontini, V. Naniyil, J. P. Stinton, D. G. Reid, J. M. F. Gunn, H. M. Price, A. B. Deb, D. Caprioli and V. Guarrera, 9 July 2025, Physical Review Letters.
DOI: 10.1103/nrjv-pwy1

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