Gerald Gabrielse and colleagues at Northwestern University kept a single positron trapped for months and brought it to its lowest energy state, New Scientist reports. The positron is the antimatter counterpart of the electron. The team also used carefully tuned microwaves to move the particle between low quantum energy states and detect the transitions, according to a Northwestern University account published by Phys.org.
Keeping the particle away from ordinary matter is essential: a positron and an electron annihilate when they meet. New Scientist describes how the researchers slowed positrons from radioactive sodium, sent them through a tungsten crystal and confined one with electromagnetic fields in an evacuated, refrigerated chamber. Northwestern puts the trap’s interior at about 300 millikelvins, or 0.3 degrees above absolute zero.
Gabrielse’s team now wants to measure the positron’s magnetic moment, a measure of its response to magnetic fields, and compare it with an earlier electron measurement. The standard model predicts the two magnetic moments should match. A difference could point to new physics and offer clues about why the universe contains far more matter than antimatter, a question physicists have yet to resolve, as New Scientist and Nature explain. The trapping and quantum control are the reported achievements; the magnetic-moment comparison is still the team’s plan.
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