Integrated 'Electronic' Circuits that Manipulate Whole Atoms Instead of Electrons


Chips with Atoms
by Philip Ball

© Macmillan Magazines Ltd 2000 - NATURE NEWS SERVICE

May 24, 2000

Integrated 'electronic' circuits that manipulate whole atoms instead of electrons may be on the horizon. Researchers in Austria have demonstrated that atoms can be guided along 'wires' on a miniaturized chip. This technology could form the basis for entirely new types of computer that are much more powerful than those currently available.

The basic currency of conventional electronics is the electron -- the tiny, electrically charged particle that circumnavigates the nucleus in an atom. Because some electrons in metals and semiconductors can wander free of specific atoms, these materials conduct electric current. Computer data is encoded as a series of these electrical pulses, typically flowing down microscopic wires of metals or semiconductors on silicon chips.

But a currency conversion is now proposed by Jörg Schmiedmayer of the University of Innsbruck, Austria and colleagues in the journal Physical Review Letters1. They demonstrate that it is possible to move atoms down chip-sized wires just ten thousandths of a millimetre wide. The researchers believe that these 'atom currents' could be made to interact with one another, performing computational operations as electrons do. Whereas normal circuitry carries electrons inside wires, 'atomic currents' are carried above. The wires act as a kind of magnetic guide, showing the atoms where to go.

In the team's system, wires are inscribed into a gold-plated semiconductor chip by etching away 'ditches' either side of the wire. When conventional electrical current is passed through the gold wires, they become encircled with a tube-like magnetic field, (this principle, electromagnetic induction, is the basis for electric motors). By combining this magnetic field with another produced by nearby, thicker wires, the researchers create a kind of 'magnetic canyon' running along the wires. Cold magnetic atoms released into this canyon spread along it, like a swarm of bees hovering inside a deep gully.

Guiding the atoms into the magnetic canyon is difficult. To get bees into a gully, the best thing would be to trap them first -- and this is the approach Schmiedmayer and colleagues take with the lithium atoms they use. They confine them in a so-called 'magneto-optic' trap, which uses magnetic fields and laser beams to marshal a gas of atoms into a small space. Restricting the atoms' motions, in effect, cools them down. The atoms need to be cold to stay in the magnetic canyon; if they move too vigorously, they can pop out over the 'cliffs'.

Schmiedmayer and his co-workers first demonstrated magnetic guidance of atoms down a wire last year2. But those wires were free-standing: made of tungsten, and a little thinner than a human hair. By scaling the technique down to a flat, chip-sized system, the Austrian team demonstrates that, in principle, 'atomic' circuitry can be miniaturized to the same degree as electronics.

But why compute with atoms, when electrons seem to work perfectly well? One prime reason is that, unlike electrons, groups of atoms can be coaxed into so-called 'coherent quantum states' known as Bose-Einstein condensates. Such states are needed to realize the hypothetical quantum computer, which exploits the laws of quantum theory to achieve a computing power far greater than is possible in conventional computers.

One tricky question is what we should call 'electronics' based on atom currents. 'Atomics' doesn't seem quite right. But there is no rush to find a new name just yet -- it will surely take time to develop the atom-guiding technique into useful processes.

Folman, R. et al. Controlling cold atoms using nanofabricated surfaces: atom chips. Physical Review Letters 84, 4749-4752 (2000). Denschlag, J., Cassettari, D. & Schmiedmayer, J. Guiding neutral atoms with a wire. Physical Review Letters 82, 2014-2017 (1999).

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