Chips with Atoms
Source: Nature.com
http://helix.nature.com/nsu/000525/000525-8.html
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).
by Philip Ball
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