One Particle of Antimatter, Held Still for Months

One Particle of Antimatter, Held Still for Months

Antimatter is famously hard to keep. A positron — the antimatter counterpart of an electron, with the same mass but the opposite electric charge — vanishes in a burst of energy the moment it meets ordinary matter. You cannot put it in a bottle, because touching the bottle would destroy it.

Now, for the first time, physicists at Northwestern University have coaxed a single positron into an exquisitely controlled quantum state and held it there for months. The study, “One-positron quantum cyclotron”, was published on 21 October 2026 in Physical Review Letters.

A container with no walls

The team, led by Gerald Gabrielse with PhD student Thomas Myers as first author, used a state-of-the-art Penning trap: specialised electric and magnetic fields that suspend the positron in empty space, in a near-perfect vacuum. Sitting in the middle of the container, the positron never touches anything.

Catching it was its own challenge. The positrons came from the radioactive decay of sodium-22, and emerged carrying enormous amounts of energy. The team slowed one dramatically, guided it into the trap, and cooled the interior to about 300 millikelvins — just 0.3 degrees above absolute zero.

“We cool it down so much that it’s in its quantum ground state,” Gabrielse said. “We actually coaxed this very fast positron to sit there and behave for months at a time.”

In that state, the positron behaves much like an artificial atom, with quantum energy levels the scientists can precisely control and observe. By delivering carefully tuned microwaves, they added tiny, precise amounts of energy and detected the positron’s individual quantum jumps between energy states.

Why hold one particle so carefully?

The advance could enable the most precise test yet of a fundamental symmetry. According to the Standard Model of particle physics, electrons and positrons should be nearly perfect mirror images of one another. Gabrielse’s team previously used a one-electron quantum cyclotron to measure the electron’s magnetic properties to about one part in 10 trillion — among the most precise measurements ever made of an elementary particle. The plan now is to make the same kind of measurement with a positron, and put the two results head to head.

If the measurements match, as current theory suggests, the Standard Model survives its most stringent test yet in this area. If they do not match, the difference would reveal a crack in the model — and a possible clue to one of physics’ biggest mysteries: the Big Bang should have created equal amounts of matter and antimatter, which would have annihilated and left nothing. Yet the observable universe contains overwhelmingly more matter than antimatter, and the Standard Model cannot explain why.

“Current theories suggest that there will be no difference in the two measurements,” Gabrielse said. “If it turns out they are not equal, that would be the biggest discovery in physics in the last century.”

The new paper does not yet report that comparison. It demonstrates the trapping and quantum control that make the comparison possible — the essential building blocks for the measurement to come.

For students, this is physics at its most patient: one particle, held still for months, so that a single number can be measured well enough to test our best theory of the universe. Big questions are often answered by the smallest, most careful experiments.

If your child is fascinated by particles, forces and “why does anything exist at all?”, a physics tutor can connect that wonder to the curriculum — from electric and magnetic fields to energy levels and the Standard Model. Book your first lesson and compare verified physics tutors, online, in person or in a group class.

Sources:

• Northwestern University, “Scientists trap and tame a single particle of antimatter for months”, October 2026: https://news.northwestern.edu/stories/2026/10/scientists-trap-and-tame-a-single-particle-of-antimatter-for-months?fj=1