New Experiment Confirms Antimatter Is Both a Particle and a Wave

For a long time now, physicists have known that almost everything- light, forms of energy and even every atom in our body exists as both particles and waves. This concept, known as particle-wave duality, has been demonstrated again and again in experiments. But antimatter particles, which are basically like their matter counterparts possessing opposite charge and spin, are much more challenging to experiment with. These twins of matter flash into existence fleetingly, typically in massive particle accelerators. But now we know that the particle-wave duality holds true even at the level of a single antimatter particle.

Recently, physicists demonstrated at the level of a single position, which is an antimatter twin of the electron, that antimatter is made of both particles and waves.

To prove that positrons are also waves, physicists designed a more complicated version of 1972’s famous “double-slit experiment,” which first showed that electrons, the basic form of matter, are both particles and waves.

During the first double-slit experiment, scientists launched a stream of electrons through a sheet with two slits on it, placing a detector on the other side. If the electrons were only particles, they would have just formed a pattern of two bright lines on the detector. But as they act like waves, they “diffracted” like light, creating a spread-out pattern of many alternating brighter and dimmer lines.

A schematic of the canonical double-slit experiment, which creates characteristic fringes of light and dark lines.

In 1976, physicists successfully figured out a way to demonstrate the same effect with just one electron at a time, demonstrating that even single electrons are waves that can “interfere” with each other.

Since then, physicists have shown that when positrons are bounced off a reflective surface, they behave like waves. But till now, they had never achieved a double-slit experiment displaying the wave nature of individual positions. Conducting such experiment offers physicists opportunities to carry out an in-depth study of the behavior of antimatter that’s deeper than ever before.

For this research paper, published on May 3rd  in the journal Science Advances, a team of Italian and Swiss physicists worked out a way to generate a low-energy beam of positions that could be utilized to perform the first antimatter version of the double-slit experiment. When these physicists directed the stream of positrons through a more complex series of multiple slits, they landed on the detector in a pattern projected from waves, not individual particles.

Paola Scampoli, a physicist at the Politecnico of Milano and co-author of the paper, said in a statement, “Our observation … proves [the positron’s] quantum-mechanical origin and thus the wave nature of the positrons.”

The authors wrote that this work, ushers in a new kind of “interferometry” experiment. They now hope to answer questions about the wave nature of more complex exotic matter and use their results to probe the nature of gravity at very small scales.

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