A single particle of antimatter has remained in a laboratory trap for months while researchers control its quantum motion. Northwestern University described the positron experiment on October 21, following the team's paper on a one-positron quantum cyclotron.
A positron is the electron's antimatter counterpart. Keeping it away from ordinary matter is essential because contact can annihilate the pair. The researchers suspend it with electric and magnetic fields inside a near-perfect vacuum.
The apparatus is a Penning trap, which confines a charged particle without letting it touch a wall. Northwestern says the trap's interior is cooled to about 300 millikelvins, or 0.3 degrees above absolute zero.
Cooling and isolation allow the team to work with individual quantum energy levels. Carefully tuned microwaves change the positron's energy, and the researchers detect the resulting transitions.
The goal is a more precise measurement of its magnetic moment, a property describing how the particle interacts magnetically. The team wants to compare that result with an earlier electron measurement.
That comparison tests a fundamental symmetry of the standard model, the theory describing elementary particles and their interactions. A more demanding test needs control of the experimental system before it needs a claim of new physics.
This experiment does not report a discovered difference between matter and antimatter. It establishes the one-particle quantum apparatus needed for sharper measurements. The experiment establishes control of one antimatter particle.
