Nobody had ever sent positronium through a diffraction grating and seen it behave as a wave. A team at Tokyo University of Science now has. Their paper, “Observation of positronium diffraction,” appeared in Nature Communications on 23 December 2025, with Yugo Nagata, Riki Mikami, Nazrene Zafar and Yasuyuki Nagashima as authors.
Positronium pairs an electron with a positron, the electron’s antimatter counterpart. The two orbit a shared center. Left alone in a vacuum it acts as a neutral atom until it self-annihilates, and that short life has made it very hard to handle.
A beam with enough discipline
Making the beam took several steps. The team produced negatively charged positronium ions first, then fired a precisely timed laser pulse to strip the extra electron. What was left was a fast, neutral, well-defined stream of positronium atoms.
Compared with earlier techniques, the beam is more energetic, up to 3.3 keV, with a narrower energy spread and a tighter path. It ran in ultra-high vacuum, which helped keep the graphene target clean.
That target was a sheet of two to three layers of graphene. Its atomic spacing lines up closely with the de Broglie wavelength of positronium at the energies in use. Some atoms passed through and hit a position-sensitive detector, and the signal there showed a clear diffraction pattern.
One wave, not two particles
The pattern settled a question about the pair itself. The electron and positron did not act independently while diffracting. The researchers checked whether positronium produces interference the way a lone particle such as an electron does, and it does.
“Positronium is the simplest atom composed of equal-mass constituents, and until it self-annihilates, it behaves as a neutral atom in a vacuum,” Nagashima said. “Now, for the first time, we have observed quantum interference of a positronium beam, which can pave the way for new research in fundamental physics using positronium.”
Nagata described the work as “a major advance in fundamental physics,” and said it opens “pathways for precision measurements involving positronium.”
Uses down the road
Since positronium has no electric charge, it may suit non-destructive analysis of surfaces, including insulators and magnetic materials that charged beams handle poorly.
The group also sees a route to testing antimatter and gravity. How antimatter responds to gravity is still an open question, because no direct measurement exists, even for electrons.
Sources
Sources
- Scientists catch antimatter “atom” acting like a wave for… | ScienceDaily
- Researchers Capture Quantum Interference in One of Nature’s Rarest…
