After placing a single particle of antimatter into a controlled quantum state for the first time, Northwestern University physicists say they may be one step closer to putting the Standard Model of particle physics to a crucial test.
The Northwestern team described its achievement in controlling a positron, the antimatter counterpart of an electron, in a recent paper published in Physical Review Letters.
The team held the elusive antiparticle for months, trapping it in a vacuum at temperatures near absolute zero to create an artificial atom known as a one-positron quantum cyclotron. Researchers then manipulated and observed the antimatter particle’s energy levels to study its quantum states.
Matter Vs Antimatter
Although we often think of matter and antimatter as mirror images, this conception is somewhat oversimplified. Their corresponding particles have identical masses and opposite electric charges, but previous experiments have revealed subtle differences in how certain particles and antiparticles decay, a phenomenon known as charge-parity violation (CP violation).
While CP violation is incorporated into the Standard Model of particle physics, the effects observed so far appear insufficient to explain why matter overwhelmingly dominates antimatter in the universe today. Understanding this imbalance remains one of the most significant unanswered questions in modern physics.
Investigating the fundamental relationship between matter and antimatter is at the heart of the team’s work. Their goal is to measure the magnetic properties of a positron with unprecedented precision and compare them with those of an electron. If physicists identify a significant difference, it could point to a major gap in the Standard Model and potentially offer new clues about the universe’s matter–antimatter imbalance.
Something Wrong with the Big Bang
“Antimatter gets its popular charm from science fiction,” said Northwestern’s Gerald Gabrielse, who led the study. “If you take an electron and an anti-electron (or positron) and collide them together, they both disappear. We describe that as annihilation, a concept that fuels science fiction writers’ imaginations.”
“The big mystery of the universe is the Big Bang should have created equal amounts of matter and antimatter. But, if that were true, it would annihilate, and we’d be left with nothing,” Gabrielse continued. “There’s clearly something wrong with that theory, and that’s what we’re trying to figure out.”
Although the Standard Model, which describes fundamental particles and three of the four known fundamental forces, has proven remarkably accurate in its predictions, physicists know it cannot explain everything. Important pieces of the puzzle remain missing, particularly concerning the relationship between matter and antimatter and the processes that shaped the early universe.
Antimatter Fireworks
Positrons, antiprotons, and antineutrons are the antimatter counterparts of the familiar electrons, protons, and neutrons that make up ordinary matter. When corresponding matter and antimatter particles meet, they can annihilate, releasing energy. This makes capturing antimatter especially challenging, since contact with ordinary matter can destroy the particles researchers are attempting to study.
For this experiment, the team captured a positron produced by the radioactive decay of sodium-22 and suspended it in electric and magnetic fields for months, preventing destructive contact with ordinary matter. The Northwestern researchers then used microwaves to precisely manipulate the particle’s quantum energy states and observe transitions between them.
While the achievement does not yet provide a definitive precision measurement of the positron’s magnetic properties, it represents a significant step toward that goal. In earlier work, Gabrielse achieved a precision measurement of an electron’s magnetic properties at the level of one part in 10 trillion. He now plans to build on that work by using quantum control of the positron to achieve a comparable measurement for antimatter.
Comparing the results could subject the Standard Model to one of its most demanding tests yet.
“Current theories suggest that there will be no difference in the two measurements,” Gabrielse concluded. “If it turns out they are not equal, that would be the biggest discovery in physics in the last century.”
The recent paper, “One-Positron Quantum Cyclotron,” appeared in Physical Review Letters on October 21, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.