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Observation of Fermi Acceleration with Cold Atoms

G. Barontini1,*, V. Naniyil1, J. P. Stinton1, D. G. Reid1, J. M. F. Gunn1, H. M. Price1, A. B. Deb1, D. Caprioli2, and V. Guarrera1

  • *Contact author: g.barontini@bham.ac.uk
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Phys. Rev. Lett. 135, 025201 – Published 9 July, 2025

DOI: https://doi.org/10.1103/nrjv-pwy1

Abstract

Cosmic rays are deemed to be generated by a process known as “Fermi acceleration” in which charged particles scatter against magnetic fluctuations in astrophysical plasmas. The process itself is, however, universal, has both classical and quantum formulations, and is at the basis of dynamical systems with interesting mathematical properties, such as the celebrated Fermi-Ulam model. Despite its effectiveness in accelerating particles, Fermi acceleration has so far eluded unambiguous verifications in laboratory settings. Here, we realize a fully controllable Fermi accelerator by colliding ultracold atoms against engineered movable potential barriers. We demonstrate that our Fermi accelerator, which is only 100  μm in size, can produce ultracold atomic jets with velocities above 0.5  m/s. Adding dissipation, we also experimentally test Bell’s general argument for the ensuing energy spectra, which is at the basis of any model of cosmic ray acceleration. On the one hand, our Letter effectively opens the window to the use of cold atoms to study phenomena relevant for high energy astrophysics. On the other, the performance of our Fermi accelerator is competitive with those of best-in-class accelerating methods used in quantum technology and quantum colliders, but with substantially simpler implementation and no fundamental physics limit.

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Corrections

26 September, 2025

Correction: The omission of a word in the last sentence of the abstract has been fixed.

Focus

Mimicking a Cosmic Accelerator

Published 9 July, 2025

A mechanism for accelerating charged particles in astrophysical plasmas has been reproduced with cold atoms in an optical trap.

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Outline

Information

Phys. Rev. Lett. 135, 025201– Published 9 July, 2025
  • Received 5 March 2025
  • Accepted 13 May 2025
  • Corrected 26 September 2025
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