2-electron computing in _Science_

David Honig (honig@sprynet.com)
Fri, 16 Apr 1999 11:14:24 -0700

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Science v 284 9 Apr 99 no 5412
p289-291

Digital Logic Gate Using Quantum Dot Cellular Automata
Islamshah Amlani et. al. of Notre Dame in IN, USA.

I'll summarize. He plays dominoes with pairs of electrons confined
to quantum dots (tiny, flat electron homes).

Four quantum dots are arranged at the corners of a square.
They are linked by tunnel junctions. Because of repulsion,
if you put 2 electrons in there, they go to opposite corners.
There are two pairs of opposite corners so they're bistable.
That's your 2-electron bit.

You can flip configurations by applying differential voltages to two of the
dots of the four.

Configurations propogate if they're next to each other.

You can build majority-gates, which can perform both AND and OR.
He doesn't mention it, but you could make NOT by reversing the
+ and - bias wires.

Their device works at < 0.1 K but if you make it *smaller* it
will work at room temp. [This is the only part that isn't
explainable in a classical way. The rest of it you could model
with magnets or electrostatics.]

Crypto applications? None directly; just interesting ways to compute.
No "spooky" quantum effects used; no extra universes needed.

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