Physics & Math - Asteroid orbits modelled in a single atom

ELECTRONS can orbit the nucleus of an atom in the same way a class of asteroids orbits the sun. The work could allow for new levels of control over chemical reactions.

Many people picture atoms as mini solar systems, with point-like electrons circling a central nucleus. But early last century that model was displaced by the fuzzy uncertainties of quantum mechanics. Under quantum rule, you can't know precisely where an electron is at any given time - only where it is likely to be. If you drew a dot at each point where the electron might be, the dots would surround the nucleus in a cloud.

Now researchers led by Brendan Wyker of Rice University in Houston, Texas, have created a solar-system-like atom. They made clouds of electrons orbit the nucleus in the same way that Trojan asteroids, which precede and follow Jupiter in its orbit, circle the sun. "Now we know you can mimic a solar system inside an atom," says team member Barry Dunning, also of Rice.

To do this, the researchers turned to supersized Rydberg atoms. The outermost electron in such atoms is so energetic it lies nearly half a millimetre away from the nucleus - "a long way", according to Dunning. "It's only just hanging on."

They targeted the electron with electric field pulses that limited its location options to a narrow, comma-shaped band on one side of the nucleus, akin to where the Trojan asteroids hang out. A second electric field then forced the electron to orbit the nucleus (Physical Review Letters, DOI: 10.1103/physrevlett.108.043001). "The classical physics that you use to describe [Trojan asteroids and electrons] is identical, except in one case you're using gravitational fields and the other electrical fields," says Dunning.

"It's a very elegant experiment," says Tom Gallagher of the University of Virginia in Charlottesville. "These are fragile atoms. I'm amazed they can control them as well as they can."

Ultimately, the researchers hope to control atoms of any size, so they can choreograph chemical reactions to produce novel materials.

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