Brent Allsop (allsop@swttools.fc.hp.com)
Thu, 31 Jul 1997 10:01:53 -0600

Hal Finney <hal@rain.org>,

Thanks for the web reference. I'll have to check it out.

> We want to measure the state of a quantum system, and bring that
> measurement into the quantum computer, preserving its quantum
> nature.

Your usage of the terms like "bring into" is very vague. Do
you mean detect and represent in a classical cause and effect way even
though some of the cause/effect and representation and amplification
machinery or whatever might be quantum?

> In a classical computer, we will basically absorb the photon, and
> measure some of its state. However, because of the Heisenberg
> uncertainty principle, we will inevitably measure only a part of the
> state. Something is always lost.

But whatever the phenomenon, once it is amplified or detected
enough to represent in any computer, whether quantum or not, why can't
the particular phenomenon be virtually simulated or modeled in a
sufficiently complex classical computer? How is it that the quantum
machinery doesn't loose the information and clasical machinery losses

> Today we can bring a photon in and put it into a loop, with
> amplifiers,

My understanding of "amplification" is you use one cause and
effect phenomenon to control in a cause and effect way a completely
different, more powerful, phenomenon. A transistor uses a few moving
electrons to control the flow of many electrons - hence amplification.
Saying one amplifies a particular physical thing, like a photon,
doesn't make much sense to me. You can't amplify a single moving
electron, you can just use it to control the movement of many other
electrons. Can you help me out here?

> and preserve most of its state for some fleeting instants.

By "preserve" do you mean keep the photon in that state, or do
you mean represent the state of the photon with some other, different
and maybe amplified physical phenomenon that detected it's state?

This is all over my head so if this is too technical don't
worry about it. Maybe some day all do the required reeding to
understand more of this.

> To actually do a lot of calculations on the photon (enough to
> simulate a conscious mind!) while preserving the phase and state
> information so perfectly will be quite a feat, to say the least!

I have a real problem with misleading (or ambiguous at best)
statements like this. We can simulate a few neurons with classical
computers. Given enough classical computing and observation power we
could, theoretically, simulate, classically, all the neurons and other
relevant machinery in a brain and thereby "simulate a conscious mind"
right? Are you simply implying that quantum computers will give us
the required computing power to do this? Or are you talking about
some quantum phenomenon here that clasical computers, no matter how
complex, could never do?

> Hope this sheds some light for you -

Yes, definitely. Like all things, I guess, more answers
simply produce even more questions.


Brent Allsop