An antimatter atom has been measured and manipulated for the first time ever, by a Canadian-led team of physicists.
"This is the first time that anyone has ever interacted with an antimatter atom," said Mike Hayden, a physics professor at Simon Fraser University in Burnaby, B.C., describing the results published in the journal Nature Wednesday.
"We've perfomed a measurement. We've tried to look for what you might call a sign of a fingerprint of this atom. You could think of it like trying to communicate with this atom, or manipulate it."
That's no easy feat — antimatter is very difficult to keep in existence because the moment it touches matter, which makes up most of our universe, both the matter and antimatter are annihilated, producing pure energy.
Antimatter is made up of "antiparticles" that have the same mass as corresponding particles of matter, but an opposite charge. For example, the antimatter counterpart of a negatively charged electron is a positively charged positron.
The new study involves measurements of antihydrogen, the antimatter counterpart of a hydrogen atom.
The measurements became possible after the ALPHA collaboration — an international group of scientists that includes Hayden and a number of other Canadians — developed a technique to make and hold antihydrogen atoms in a magnetic trap, keeping them away from the sides of their container, which is made of matter.
"We hold them without actually touching them," Hayden said.
The researchers figured out how to keep the antimatter atoms trapped for up to half an hour — enough time to run experiments on them.
Comparing matter and antimatter
Ideally, scientist would like to get a detailed chemical fingerprint of antihydrogen to be able to compare it to hydrogen.
They hope that doing so will help them understand one of the great mysteries of the universe — why it is almost entirely made up of matter, even though matter and antimatter are thought to have been originally produced in equal amounts at the time of the Big Bang.
The answer may lie in small differences between the properties of matter and those of antimatter. But until now, scientists haven't been able to compare them.
The first measurements of antihydrogen suggest that the fingerprint of an antimatter atom is very similar to that of its matter counterpart.
"There's no wildly different result. It looks like an ordinary hydrogen atom," Hayden said.
But he emphasized that this first measurement is very rough — more notable as proof that antimatter atoms can be measured than as a result in itself. It wasn't expected to have enough precision to detect a difference between matter and antimatter.
"If there's a difference," Hayden added, "everyone's betting it's going to be subtle."
Flip and shove
The experiment described in the new paper involved placing the antimatter atoms in a trap and then hitting them with the "right" combination of a magnetic field and a certain frequency of microwave radiation. The researchers picked a combination that hydrogen atoms are known to respond to.
Hydrogen atoms in their lowest energy state naturally line themselves up with magnetic fields — a property known as "spin" that antihydrogen atoms also appear to have.
In fact, the antimatter atoms need to be lined up in a certain direction in order to remain in the magnetic trap.
When hydrogen atoms are hit with just the right microwave frequency in combination with the magnetic field, the magnets inside the atoms flip the other way, Hayden said.
When that happens, they are no longer properly lined up with the magnetic field of the trap. The same thing happens to antimatter atoms.
"They literally get a shove out and go crashing into the wall," Hayden said.
At that point, they get annihilated, since the wall is made of matter, and the energy of annihilation can be measured.
The researchers found that the "right" combination of magnetic field and frequency caused 10 times more antimatter atoms to leave the trap and get annihilated than the "wrong" combination.
However, Hayden noted that the measurement isn't considered precise because researchers did not systematically run the experiment with different combinations of conditions to see where they would get the biggest signal.
The researchers are in the process of upgrading their equipment so they can make a wider range of more precise measurements using devices such as lasers.
"You want to measure as many different properties as you can," Hayden said, "to get the best possible fingerprint for this atom."