Physicists Suspend a Single Positron in a Quantum Cyclotron

Researchers at Northwestern University have suspended a lone positron—the antimatter counterpart of the electron—in mid-air using a one-positron quantum cyclotron and cooled it to its lowest possible energy state. The team captured fast positrons from radioactive decay, slowed them by scattering off a tungsten crystal, discarded those that annihilated, and fed the remaining slow particles into a magnetic trap. This achievement enables measurements of the positron’s magnetic moment with a precision up to 10,000 times greater than that achievable for electrons.

Nature

The experiment builds on decades of antimatter research that seeks subtle differences between matter and antimatter, a disparity that underlies the mystery of why the observable universe is dominated by matter. The standard model predicts equal amounts of both after the Big Bang, yet matter’s survival remains unexplained. By comparing the magnetic moments of electrons and positrons—properties that dictate how the particles wobble in a magnetic field—physicists hope to detect any mismatch that could signal physics beyond the standard model. Barbara Maria Latacz, an antimatter physicist at CERN, described the work as a “remarkable achievement” that provides a powerful probe for new physics. Stefan Ulmer of Heinrich Heine University Düsseldorf expressed enthusiasm for the forthcoming precision measurements.

Nature

Gerald Gabrielse, who led the Northwestern team, emphasized that finding a measurable difference would be “revolutionary in physics.” He noted that if matter and antimatter had been created in exactly equal amounts and subsequently annihilated, the universe as we know it would not exist. The findings were detailed in *Physical Review Letters* in October, highlighting the experiment’s potential to challenge the completeness of the standard model.

Nature

• “I cannot wait to see their first precision measurements,” — Stefan Ulmer, a physicist at Heinrich Heine University Düsseldorf (HHU) in Germany

Nature