Lasers have thrown and captured extremely cold single atoms. The technique can be used in the future to build quantum computers.
To put extremely cold atoms in certain positions, researchers usually grab them using highly focused laser beams called optical tweezers. This works because ultracold atoms are very sensitive to the forces that electromagnetic radiation, such as light, exerts on them. Physicist Jaewook Ahn of the Advanced Institute of Science and Technology in South Korea and his colleagues were now looking for a way to minimize the time the lasers “touch” the atoms. If lasers are working with the atoms for too long, the properties of the particles can be disrupted.
The researchers started with a small box, made of metal and glass, containing rubidium atoms. These atoms had a temperature of 40 millionths of a degree above absolute zero. The team gave the atoms a small kick using the laser light, which sent the atom flying towards its destination.
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There a second optical tweezer was waiting for the atom. This caught the atom and slowed it down so that it came to rest at the desired location. The distance covered in this way was up to 12.6 micrometres.
Build with atoms
According to Ahn can this method making it easier to build larger – and therefore more powerful – quantum computers that also work on the basis of ultracold atoms. In these computers, each ultracold atom stores information. They are arranged in grids, and they process information by interacting with neighboring atoms.
Throwing atoms can be useful not only for the construction, but also for the maintenance of the quantum computer. If an error occurs in the computer, an atom must be replaced or moved, says Ahn. Even then, the method can be used to quickly reconfigure the grid.
“Say you need to add an atom at the center of a grid,” says University of Wisconsin-Madison physicist Mark Saffman. ‘Usually you then have to maneuver optical tweezers along different points in the grid, which can disturb the atoms there. If you can just throw the atom to the center, you solve that problem.’
The new method still requires some improvement, says Saffman. During the study, the lasers sometimes dropped atoms before throwing them, or failed to capture the particles properly.