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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