Freezing antimatter could pin it down for study

Antimatter’s not the easiest stuff to work with – the minute it encounters ordinary matter it self-destructs. Now, though, scientists believe they’ve found a way to keep it in one place for long enough to study, by cooling it right down.

The new method, developed by a group of researchers from the USA and Canada, could potentially cool trapped antihydrogen atoms to temperatures 25 times colder than ever before, making them much more stable and a lot easier to experiment on.

It involves directing a laser at antihydrogen atoms to give them a ‘kick’, causing them to lose energy and cool down.

“By reducing the antihydrogen energy, it should be possible to perform more precise measurements of all of its parameters. Our proposed method could reduce the average energy of trapped antihydrogen by a factor of more than 10,” says Professor Francis Robicheaux of Auburn University.

“The ultimate goal of antihydrogen experiments is to compare its properties to those of hydrogen. Colder antihydrogen will be an important step for achieving this.”

This process, known as Doppler cooling, is already an established method for cooling atoms; it’s not been clear, though, whether the technique would work to trap antimatter.

But, says Robicheaux, “By doing the calculations, we’ve shown that this effort is worthwhile.”

Through a series of computer simulations, his team has shown that antihydrogen atoms could be cooled to around 20 millikelvin; trapped antihydrogen atoms so far have energies up to 500 millikelvin.

In 2011, researchers from CERN managed to trap antimatter for over 1,000 seconds. While the processes that control the trapping are largely unknown, it’s thought that laser cooling should increase this length of time.

“Whatever the processes are, having slower moving, and more deeply trapped, antihydrogen should decrease the loss rate,” says Robicheaux.

Colder antihydrogen atoms could also be used to measure the gravitational property of antimatter, says Dr Makoto Fujiwara of Canada’s National Laboratory for Particle and Nuclear Physics.

“No one has ever seen antimatter actually fall in the field of gravity,” he says. “Laser cooling would be a very significant step towards such an observation.”