One of our most precise mechanisms for controlling matter has now been applied to antimatter atoms for the first time. Laser cooling, which slows the motion of particles so they can be measured more precisely, can make antihydrogen atoms slow down by an order of magnitude.
Antimatter particles have the same mass as particles of ordinary matter, but the opposite charge. An antihydrogen atom is made out of an antiproton and a positron, the antimatter equivalent of an electron. Makoto Fujiwara at TRIUMF, Canada’s national particle accelerator centre, and his colleagues used an antihydrogen trapping experiment called ALPHA-2 at the CERN particle physics lab near Geneva, Switzerland, to create clouds of about 1000 antihydrogen atoms in a magnetic trap.
The team developed a laser that shoots particles of light called photons at the right wavelength to slow down any anti-atoms that happen to be moving directly towards the laser, slowing them down bit by bit. “It’s kind of like we’re shooting a tiny ball at the atom, and the ball is very small, so the slowing down in this collision is very small, but we do it many times and then eventually the big atom will be slowed down,” says Fujiwara.
The group managed to slow the anti-atoms down by more than a factor of 10. Laser cooling is often used to measure energy transitions – the movement of electrons to different energy levels – in regular atoms, and for cooled antihydrogen atoms, the team’s measurement of this was nearly three times as precise as it was with uncooled anti-atoms.
“This is really an exciting milestone for us, but what’s even more exciting is the things that this allows us to do in the future – the new kinds of measurements and experiments that were unthinkable before with antimatter,” says Fujiwara. Most of these possibilities are related to the extremely precise measurements that must be made to search for any tiny differences in the behaviour of matter and antimatter.