Northwestern University physicists trapped and cooled one positron in a controlled quantum state for months, creating a tool to compare antimatter with matter and test a basic prediction in particle physics.
A positron is the antimatter version of an electron, with the same mass but the opposite electric charge. It is destroyed when it meets ordinary matter. The team captured positrons produced by radioactive sodium-22 decay.
It then held one positron in a Penning trap, where magnetic and electric fields kept it from touching the trap’s walls. Cooling the apparatus to about 300 millikelvins and removing nearly all gas from the chamber helped the researchers prepare and distinguish the particle’s lowest energy and spin states. Researchers call the setup a “one-positron quantum cyclotron” because the particle’s motion can be controlled and measured in separate steps set by quantum rules.
The researchers have not reported a new comparison between matter and antimatter yet. The achievement makes it possible to measure the positron’s magnetic moment more precisely. Comparing that measurement with the electron’s could closely test the Standard Model’s prediction that the two particles have matching properties.
Any confirmed difference could point to physics beyond that model. The experiment does not by itself explain why the universe contains far more matter than antimatter. The study was published in Physical Review Letters on October 21, 2026.