Detect positronium wave interference
- Tokyo University of Science researchers reported the first direct observation of positronium diffraction, showing the short-lived electron-positron atom can produce matter-wave interference in free space. - The Nature Communications paper measured a distinct first-order diffraction peak after an energy-tunable positronium beam passed through two-to-three-layer graphene and hit a detector. - The result gives positronium interferometry a real experimental footing for symmetry and gravity tests. (nature.com)
Positronium is an atom-like pair made from an electron and a positron, and it vanishes fast when the two annihilate. A team at Tokyo University of Science has now shown that a positronium beam also behaves like a wave. (nature.com) In quantum mechanics, particles can spread out like ripples and make bright-and-dark bands when those ripples overlap. Physicists call that diffraction or interference, and they had already measured it for electrons, neutrons, atoms, and molecules. (nature.com) (tus.ac.jp) Positronium had been the holdout in free space. The system is unusual because its two parts have equal mass, unlike ordinary hydrogen, and the triplet state survives only about 142 nanoseconds before annihilation. (nature.com) (pmc.ncbi.nlm.nih.gov) Yugo Nagata, Riki Mikami, Nazrene Zafar, and Yasuyuki Nagashima reported the result in Nature Communications, in a paper published December 23, 2025. The group used a high-quality, energy-tunable positronium beam and sent it through graphene. (nature.com) (tus.ac.jp) Graphene worked as the grating because its atomic spacing matched the positronium wavelength at the beam energies the team used. The sheet was two to three layers thick, and transmitted atoms were recorded with a position-sensitive detector. (tus.ac.jp) (nature.com) The key signal was a distinct first-order diffraction peak in the place matter-wave theory predicted. The paper says that peak provides direct evidence of quantum interference in positronium beams. (nature.com) (pmc.ncbi.nlm.nih.gov) The experiment also addresses a basic question about what is interfering. The authors say the data show positronium behaves as one quantum object, not as an electron and positron interfering independently. (nature.com) That matters because positronium is a clean test system for quantum electrodynamics, antimatter interactions, and gravity. The paper says the diffraction result opens a path to precision measurements using positronium beams, including proposed interferometry experiments on antimatter gravity. (nature.com) (pmc.ncbi.nlm.nih.gov) The team’s beam method was central to getting there. Tokyo University of Science said the researchers first made negatively charged positronium ions, then used a laser pulse to strip off an extra electron and create a fast, neutral, coherent positronium beam. (tus.ac.jp) For now, the result does not measure how antimatter falls. It shows that a short-lived antimatter-containing atom can be prepared, transmitted through a crystal-scale grating, and read out as a matter wave before it disappears. (nature.com) (sciencedaily.com)
