Re: Quantum Computation

In article <d2kdm9$o21$1@xxxxxxxxxxxxxxx>,
Ralph Hartley <hartley@xxxxxxxxxxxxxxxx> wrote:
>
>That you can set up the initial, and read the final, states is implicit
>in the definition of a Quantum Computer. If you can't do that, you don't
>have one.

Agreed.

>Of course quantum algorithms are not practical without a Quantum Computer.

Also agreed. It is one of the reasons that the computer scientists'
term "non-deterministic automaton" annoys me so much. While it is an
interesting mathematical construct, it is both solidly deterministic
and non-constructible in the physical universe if built out of
classical components.

HOWEVER, if quantum computers could be built, my understanding is that
they would almost certainly encompass non-deterministic automata, and
so all that theory would become directly relevant.

>All the proposed implementations I have seen are programmable. Typically
>they allow a complete set of operations to be performed in an arbitrary
>order (the sequence of operations is classically determined, but that's
>all you need). They are complete for quantum computation.

Do you have any references that are clear enough to describe what can
and cannot be done in a particular design? I am particularly interested
in the more complex operations, such as conditionals, loops, absolute
values and so on.

>All *actual* implementations to date have so few bits, and can perform
>so few operations before failing, that the phrase "arbitrary sequence"
>is a bit of an exaggeration.

Well, yes. But there is also the point that the setting up of the
initial state and decoding of the final state ALSO needs to be semi-
programmable, and that is often not addressed in such research.


Regards,
Nick Maclaren.

.