Laser-beam ‘tweezers’ guide two atoms to collide

A glass cell (vertical object, centre) holds a cloud (bright spot) of 1 million sodium atoms cooled to less than 0.001 Kelvin, in preparation for combining a solo atom with a single caesium one.

Glass cell vacuum apparatus

A carefully manipulated crash shows what happens when atoms collide in the cold.

Scientists have achieved a controlled chemical reaction between exactly two atoms.

At the atomic scale, chemical reactions occur through collisions between individual atoms or molecules. To create a single collision, a team led by Kang-Kuen Ni at Harvard University in Cambridge, Massachusetts, cooled sodium and caesium atoms, then trapped one of each in laser beams of differing wavelengths to allow the atoms to be manipulated individually.

By carefully refining the direction and intensity of each beam, the researchers merged the two, guiding both atoms towards the same spot to force a collision. This produced a single sodium-caesium molecule.

The technique could be expanded to create customized complex molecules, which might be used to study states of matter at ultra-low temperatures, and to store information in quantum computers, the authors write.

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