Northwestern Physicists Trap a Single Positron for Months
A Northwestern University team held one antimatter particle for months near absolute zero, a method that could make positron measurements about 30 times more precise.
Physicists at Northwestern University have trapped a single positron, the antimatter counterpart of the electron, for months. The team cooled the particle to temperatures near absolute zero and controlled its quantum states with great precision without destroying it. The work was published in Physical Review Letters.
The team, led by Gerald Gabrielse, built a device known as a single-positron quantum cyclotron. It uses electric and magnetic fields to hold the particle in a vacuum, where it sits in its lowest energy state. In that state, researchers can induce controlled changes in its quantum behavior. Because the approach does not destroy the particle, they could repeat measurements on the same positron over months.
Why antimatter is so hard to study
Mathematics predicts that every particle of matter has an antiparticle, and experiments have confirmed it. The universe should therefore hold similar amounts of both, yet nearly everything we observe is ordinary matter. Scientists still don't know why.
Antimatter can be produced in laboratories, but when an antiparticle meets ordinary matter, the two annihilate and release energy. Researchers rely on vacuum chambers and electromagnetic fields to keep antiparticles isolated. That only partly solves the problem, and probing their behavior at the quantum scale remains difficult.
What comes next
An electron and a positron have the same mass and opposite electric charges. Open questions remain about just how alike they are, and whether small differences have slipped past earlier experiments. The researchers want to compare the magnetic properties of the two particles. Electron measurements are already very precise, but matching that precision for positrons has been harder.
According to the American Physical Society, the new device could allow measurements of antimatter particles about 30 times more precise than before. So far, the experiment has found no unexpected differences between the two particles. What it delivers is a better ability to look for them. If future measurements show that a positron responds to magnetic fields differently from an electron, scientists would have to revise some of the laws they use to describe matter and antimatter.
