Antimatter is not known for being easy to get ahold of. That’s part of why these particles remain so cryptic. But recently, a team of physicists at Northwestern University managed to trap a single antimatter particle for months. Cooling it to temperatures near absolute zero, they could control its quantum states with great precision without even touching it. The experiment, published in Physical Review Letters, represents a breakthrough in our understanding of one of the great mysteries of physics.
In theory, antimatter should be everywhere. Mathematics predicts that every particle of matter has an equivalent antiparticle, a fact that scientists have verified experimentally. The universe should therefore contain similar amounts of both, but almost everything we observe is made up of ordinary matter, and we still don’t know why.
It is possible to produce antimatter particles in laboratories, but studying them is still incredibly difficult. When an antiparticle comes into contact with ordinary matter, the two annihilate each other and release energy. To prevent research facilities from exploding, scientists use vacuum chambers and electromagnetic fields that suspend the antiparticles in isolation. But this only partially solves the problem. Studying these particles, especially experimenting with their behavior on a quantum scale, remains challenging.
For this experiment, researchers at Northwestern trapped a positron, the antimatter counterpart of electrons. The team, led by Gerald Gabrielse, developed a device known as a single-positron quantum cyclotron, which used electric and magnetic fields to hold the positron in a vacuum at a temperature close to absolute zero. This means the antimatter particle was at its lowest energy state, allowing the researchers to induce controlled changes in its quantum behavior. Unlike other methods in particle physics, this approach didn’t destroy the particle. The researchers were therefore able to keep the single antiparticle trapped for months, allowing them to repeat measurements.
So what can taming antimatter particles actually teach us? Scientists know that matter and antimatter have very similar properties. For example, an electron and a positron have exactly the same mass, although their electric charges are opposite. However, questions still remain about exactly how similar these two forms of matter are and whether there are small differences that have gone unnoticed in experiments conducted to date.
To this end, researchers want to compare the magnetic properties of both particles. Physicists have already made very precise measurements with electrons, but achieving the same level of precision with positrons has proven more difficult. According to the American Physical Society, the new device could enable measurements of antimatter particles about 30 times more precise than scientists were capable of before.
So far, the experiment has not revealed any unexpected differences between the two particles. What the researchers have achieved is an improvement in their ability to detect these differences in antimatter particles. If future measurements find that a positron responds to magnetic fields differently than an electron, scientists would have to revise some of the laws they use to explain the behavior of matter and antimatter.
This story originally appeared in WIRED en Español and has been translated from Spanish.