Quantum Physics Discovery
Quantum physics is fundamentally distinguished from classical physics by the observation that matter exhibits different behaviors at the smallest scales. A key discovery in this field is wave-particle duality, which reveals that particles can also demonstrate wave-like properties.
The double-slit experiment famously illustrates this duality. When electrons are directed through two slits, they produce an interference pattern on a detector, indicating that each electron behaves as a wave, with its quantum wave-function passing through both slits and interfering with itself. This phenomenon has been confirmed for various atomic systems, including neutrons, helium atoms, and larger molecules. However, direct observation of matter-wave diffraction in positronium, a short-lived two-body system of an electron and a positron, had not been achieved.
Positronium Diffraction Achieved
Researchers from Tokyo University of Science, led by Professor Yasuyuki Nagashima, along with Associate Professor Yugo Nagata and Dr. Riki Mikami, have successfully demonstrated matter-wave diffraction for positronium. The findings were published in the journal Nature Communications on December 23, 2025.
The positronium beam utilized in this study possessed sufficient energy variability and coherence to observe the interference effects. Professor Nagashima noted that this observation of quantum interference in positronium, the simplest atom composed of equal-mass constituents, could facilitate new research in fundamental physics.
Methodology
This achievement was made possible by developing a high-quality positronium beam. The researchers generated the beam by first creating negatively charged positronium ions, then using a precise laser pulse to remove an extra electron. This process yielded a fast, neutral, and coherent beam of positronium atoms.
The tunable beam was then directed at a two-to-three-layer graphene target. The atomic spacing of graphene is well-matched to the de Broglie wavelength of positronium at the energies used. As the positronium atoms passed through the graphene sheet, some were transmitted and subsequently detected using a position-sensitive detector, which revealed a clear diffraction pattern.
Significance and Future Applications
This approach produced positronium beams with higher energies (up to 3.3 keV) and a much narrower energy spread compared to previous methods. The beam can also be generated in ultra-high vacuum, ensuring a clean graphene surface for clear observation of diffraction effects. The results demonstrate that positronium, despite consisting of two particles, behaves as a single quantum object, with the electron and positron not diffracting independently.
Dr. Nagata stated that this experimental milestone represents a significant advance in fundamental physics. It confirms positronium's wave nature as a bound lepton–antilepton system and opens pathways for precision measurements involving positronium. The researchers also confirmed that positronium interferes as a single particle, similar to an electron.
Beyond confirming its quantum properties, positronium diffraction offers several potential applications. Its electrical neutrality allows for non-destructive, surface-sensitive analysis of materials, including insulators or magnetic surfaces that would otherwise disrupt charged particle beams. In the long term, positronium interference experiments could enable sensitive tests of gravity using antimatter, an area where direct measurements are currently lacking.