Re: Quantum Computing

From: Tommy McCabe (
Date: Sun Jul 25 2004 - 12:29:52 MDT

--- fudley <> wrote:
> There is an interesting paper in the July 22 issue
> of Nature, a UCLA
> team succeeded in flipping a single electron spin
> upside down in an
> ordinary commercial transistor chip, and detected
> that the current
> changes when the electron flips.
> Hong Wen Jiang, a UCLA professor of physics and
> member of the California
> NanoSystems Institute, in whose laboratory the
> experiments were
> conducted said, "Our research demonstrates that an
> ordinary transistor,
> the kind used in a
> desktop PC or cell phone, can be adapted for
> practical quantum
> computing,
> The research makes quantum computing closer and more
> practical. I would
> not be surprised one day to see a quantum computer
> built, based almost
> entirely on silicon technology.
> Eli Yablonovitch, co-author of the Nature paper
> said,
> "We've done this with a commercial silicon
> integrated circuit chip,
> literally off a shelf. We've manipulated one spin, a
> year from now,
> manipulating a single spin might be all in a day's
> work, and in 10
> years,
> perhaps it will have a commercial role. With 100
> transistors, each
> containing one of these electrons, you could have
> the implicit
> information storage that corresponds to all of the
> hard disks made in
> the world this year, multiplied by the number of
> years the universe has
> been around. And why stop with 100
> transistors?"

There is no reason to stop with 100 transistors.
However, in order to get a capacitance of "all the
hard disks (~1*10^11 bytes each) * made this year
(~1.5^10^8) * the number of years this universe has
been around (~1.3*10^10)", with 100 transistors, each
transistor would have to have a capcity of 1.95*10^27
(feel free to check my math) bits. That strikes me as
unlikely, considering that is larger than the number
of atoms in an entire chip with millions of
transistors. Going by my math, if there is only 1
electron that changes spin per transistor, and there
are only two states for each electron, there are 2^100
(which is around 10^32) states for the chip to be in,
but only 100 bits of storage capacity, which is puny
even by 1960's standards.

> John K Clark

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