New method aims to trap coldest antimatter yet

This process, known as Doppler cooling, is an established method for cooling atoms.

Updated: Jan 07, 2013, 17:59 PM IST

Washington: Scientists have devised a new method of cooling down antimatter that will make it easier to experiment on, and also map its mysterious properties that yet remain elusive.

The new method for cooling trapped antihydrogen could provide `a major experimental advantage`, researchers from the US and Canada believe.

The technique could potentially cool trapped antihydrogen atoms to temperatures 25 times colder than already achieved, making them more stable and a lot easier to experiment on.

The suggested method involves a laser which is directed at antihydrogen atoms to give them a `kick`, causing them to lose energy and cool down.

Antihydrogen atoms are formed in an ultra-high vacuum trap by injecting antiprotons into positron plasma. An atomic process causes the antiproton to capture a positron which gives an electronically excited antihydrogen atom.

As it is only possible to trap very few antihydrogen atoms, the main method for reducing the high energies is to laser cool the atoms to extremely low temperatures.

"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," co-author of the study, Professor Francis Robicheaux of Auburn University in the US, said.

"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," Robicheaux said in a statement.

This process, known as Doppler cooling, is an established method for cooling atoms; however, because of the restricted parameters that are needed to trap antimatter, the researchers need to be absolutely sure that it is possible.

"It is not trivial to make the necessary amount of laser light at a specific wavelength of 121 nm. Even after making the light, it will be difficult to mesh it with an antihydrogen trapping experiment. By doing the calculations, we`ve shown that this effort is worthwhile," continued Robicheaux.

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

Colder antihydrogen atoms could also be used to measure the gravitational property of antimatter.

"No one has ever seen antimatter actually fall in the field of gravity. Laser cooling would be a very significant step towards such an observation," said co-author Dr Makoto Fujiwara of TRIUMF, Canada`s National Laboratory for Particle and Nuclear Physics.

The study was published in Journal of Physics B: Atomic, Molecular and Optical Physics.