Quantum Theory?

Loomer

I have just been reading an excellent book, The Code Book by Simon Singh which I highly recommend. Being a physics n00b I wonder could anyone elaborate on some material that was touched in the book, namely Quantum Theory. It talks about the two camps behind the theory - superposition and multi-universe.
I had a basic understanding of Schroedingers Cat experiment from previous reading which supports the superposition.
But as a layperson the idea of the dual states represented seems to me to be like shaving a square block to make it fit in a round hole. To apply this theory ala quantum computing seems to be an exercise in futility, while at this stage no device exists that could perform the required function has such a model been tested on a computer?

Any takers?

MiCr0

[ot]
read the codebreakers by david kahn if you can
its better that the code book (which is very good none the less)

scipio_major

Currently working my way through "The Code Book" too. It really is a great read. It seems that every book on cryptography published after "The Bible Code" has to slam it somewhere. Do anyone believe that there is hidden imformation encoded in the bible anymore? I read another book about a imformation encoded in King James Bible by the Knights templar. If you do something to the book of psalms you can get the herbal remedies to a shovel load of diseases. I'm wondering has anyone read that book (which was banned in Britain I think)?

Fade to Credits
Scipio_major

bonkey

If you guys want a "crypto" discussion, Id suggest taking it to another thread/forum. Lets stick with what was asked here....

OK...the basic idea is that "individual" polarised photons can have their polarisation checked. If you use a correcly oriented polarisation mask, then there is a 100% chance that you will get a signal through. However, due to the uncertainty principle and some clever applications thereof, if the mask is wrong, there is still a 50% chance that you get a signal through anyway.

Now.....here's the clever bit. Unless you measure a "signal" with the correct mask, you interfere with the signal, which means that you have no way of recreating it, and the 50% uncertainty means that you cannot be sure of your correctness/incorrectness.

So, what we end up with is a system whereby you cannot intercept the signal without interfering with it, and therefore you have security.

I think that Singh over-explains quantum theory a bit for what he needs, without explaining it enough to make what he says fully understandable.....if you see what I mean

Anyway - its no longer just theory. Quantum encryption machines have been created and tested, and may even be commercially available at this stage (very limited, line-o-sight, expensive). Also, there is no effective way of getting around them...

Of course.....its all somewhat misleading, because unless we move to an all optical world, all it means is that your signal from transmitter to receiver cannot be "overheard" by a third-party. However, since its using an optical wireless technology, one has to wonder at whether or not it is any more secure than existing LOS technologies such as laser, where the only way to intercept the signal anyway is to put a bloody big splitter in the path of the beam, which would be noticed.

In short, I cant see huge applications for this, until they start using quantum crypto over fibre-optic cable.

jc

nesf

Hmm, I agree completely with Bonkey, I feel he explained it rather well. But tbh, it's not a nice area to study from a q.m. approach, unless you've studied it. I'd recommend looking at crypto approaches and explanations first.

Loomer

While I value you your input, no one has clarified why to a physics layman like myself the whole quantum theory idea sounds like a Confucious saying - If a tree falls in a forest and there is no one to hear it does it make a sound yada yada yada. (Which from a Quantum point of view as I understand it, because no one is there it satisfies both states - making a sound and not making a sound )
So can anyone shed any light on whether Quantum Computing is based purely on convenient Hypothesis and has no and will have no basis in actual fact?

bonkey

Originally posted by Loomer
So can anyone shed any light on whether Quantum Computing is based purely on convenient Hypothesis and has no and will have no basis in actual fact?

Oh - thats all you wanted to know?

That one is simple.

Quantum Computing has been proven, using (I believe) up to 7 "nodes". This is for the opposite of what you asked - using QM computers to *break* encryption through superposition allowing all states to be calculated at once.

Using QM to *encrypt* is well further progressed - as I said, I believe there are commercial systems (or at worst commercial prototypes) which already utilise this, but as I mentioned in my previous post, I'm not convinved of its utility yet.

Quantum Theory is well-established as a model which fits observed "phenomena" - typically at a scale where any form of relativity falls apart. Quantum tunnelling, quantum interference, etc have all been observed, and the theory predicts/ecplains this behaviour.

In the same way that relativity was quite helpful in building the atom bomb, despite being an incomplete theory, QT is helpful in leading to areas like Q-Computing (Qomputing?) and Q-encryption. These are not wishful thinking - they are proven fact, tested, and at various stages of being turned into products.

jc