Researchers at Tokyo University of Science have demonstrated matter-wave diffraction in positronium, an exotic atom formed by an electron and its antimatter counterpart, a positron. This marks the first observation of quantum interference in such a system. The findings, published in Nature Communications, confirm positronium's wave-particle duality.
A team led by Professor Yasuyuki Nagashima, along with Associate Professor Yugo Nagata and Dr. Riki Mikami at Tokyo University of Science in Japan, produced a high-quality beam of positronium atoms. They generated negatively charged positronium ions and used a laser pulse to strip away an extra electron, creating a fast-moving, neutral, and coherent stream. This beam, with energies up to 3.3 keV, was directed at a thin graphene sheet in an ultra-high vacuum environment, where some positronium atoms passed through and produced a clear diffraction pattern on detectors, indicating wave-like interference as a unified quantum object rather than separate particles for the electron and positron. The graphene's atomic spacing matched the positronium's de Broglie wavelength, enabling the observation of this quantum effect previously seen in electrons, neutrons, and larger molecules but not in positronium until now. Positronium, which self-annihilates quickly, behaves as a neutral atom until then, making it ideal for such studies. The experiment's precise control over beam energy, direction, and coherence yielded sharper results than prior methods. Professor Nagashima stated, '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.' Dr. Nagata added, 'It not only demonstrates positronium's wave nature as a bound lepton-antilepton system but also opens pathways for precision measurements involving positronium.' This breakthrough could enable non-damaging surface analysis of insulators and magnetic materials using charge-neutral positronium, and future tests of antimatter's response to gravity, which remains unmeasured directly.
