For the first time, Northwestern University physicists have coaxed a single positron—the antimatter counterpart of an electron—into an exquisitely controlled quantum state.

After capturing the fast-moving particle from radioactive decay, the scientists cooled it to nearly absolute zero. Then, they suspended the particle in a near-perfect vacuum, preventing it from touching ordinary matter—an encounter that would cause it to vanish.

By trapping and cooling a positron this way, the scientists created what they call a “one-positron quantum cyclotron.” In this state, the positron essentially behaves much like an artificial atom with quantum energy levels scientists can precisely control and observe.