Atom as a light dimmer

Properties of the atom are changed arbitrarily with control laser

Laser physicists at the University of Bonn have developed a kind of "light dimmer" from a single atom. © Volker Lannert / University of Bonn
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Bonn physicists have developed a kind of "light dimmer", which consists of a single atom. He is served by a laser beam. In the future, similar components will probably be used in quantum communication, the researchers report in the journal Physical Review Letters.

One of the great attractions in Germany's flagship express train, the ICE-3, is the glass wall between the driver's cab and the lounge: it's usually clear. A push of a button, however, is enough, and it turns - Abrakadabra - from now on the same in opaque milk glass.

Quantum physicists at the University of Bonn master a similar magic trick. With one difference: they work with individual cesium atoms, which on request make them "transparent" or more or less "opaque".

Cesium atom in the "light cage"

For their new experiment, the researchers around Professor Dieter Meschede used arched mirrors with extremely high reflectivity. They aligned the mirror surfaces so that they faced each other. A ray of light can be thrown back and forth between the mirrors hundreds of thousands of times.

In this "light cage" they now placed a single cesium atom. With a control laser irradiated from the side, they then very specifically changed the properties of this atom. For example, they managed to let the light pass through the cage, weaken it, or even block it off - much like a dimmer. display

That one can use cesium as a pure on-off switch, the Bonn researchers have already been able to show a year ago. "But now we can change the properties of the atom with our control laser exactly as we want it, " says Tobias Kampschulte from the Bonn Institute for Applied Physics.

Nice effect: the cesium gets colder

The physicists are particularly pleased about an unexpected effect of their experiment: Cesium atoms are quite lively at room temperature. In order to be able to manipulate them specifically, the researchers therefore cool the atoms until they barely move. Then grab them with a kind of tweezers of light and hold them in the desired location. But even when chilled, the atoms are still so fidgety that on average they can only be held for a mere second. Then they take off.

In the optical cage, however, the cesium sits still much longer under the influence of the control laser - on average 16 seconds. This leaves the physicists more time for their experiments.

"Our experimental setup seems to continue to cool the cesium atoms and thus hold them longer, " explains Kampschulte. Why this is so, we do not know exactly.

(idw - University Bonn, 06.10.2010 - DLO)