So i was reading an article on one of the newest Quantum computing experiments...

Click here

The researchers ran each program 900 times. On average, the quantum computer operated accurately 79 percent of the time, the team reported in their paper, which was published online November 15. “Getting this kind of control over a quantum system is really interesting from a physics perspective,” Hanneke says.

Earlier research has estimated that to be useful, a quantum computer must operate accurately 99.99 percent of the time. Hanneke says that with stronger lasers and other refinements, the system’s fidelity may be improved.

I wanted more information so I read...

Click here

Specifically...

Integer factorization is believed to be computationally infeasible with an ordinary computer for large integers that are the product of only a few prime numbers (e.g., products of two 300-digit primes).[7] By comparison, a quantum computer could efficiently solve this problem using Shor's algorithm to find its factors. This ability would allow a quantum computer to "break" many of the cryptographic systems in use today, in the sense that there would be a polynomial time (in the number of digits of the integer) algorithm for solving the problem.

My question though to all you science geeks even after I read the wiki stuff is: Can anyone explain why a quantum computer is so good/fast to a laymen like me?

(I trid to make this thread interesting, not to long, contain quick info'n'quotes and 'clean' in an attempt to improve on my past threads, hope its a step up)

Both classical and quantum computers
perform calculations by manipulating
information. Classical computers
represent information as binary digits,
or bits, which can have values of
either 0 or 1. Quantum computers
represent information as quantum
bits, or qubits. Many different
physical objects can be used as qubits,
such as atoms, photons, or electrons.
Paradoxically, a qubit can represent
0 and 1, as well as other possible
values, at the same time, in what is
called a quantum superposition.
This allows a qubit to simultaneously
use many more informational
states for computation and is
responsible for quantum computing’s
advantages over classical computing.
In the illustration above, an atomic
spin represents a qubit. An “up”
spin corresponds to 0; a “down”spin
equates to 1. A quantum superposition
encompasses 0, 1 and all possible
values in between.

I took your un-necessary jab on the chin and followed your link trog, downloaded the pdf and read it in compeltion but dont really understand any better. The above i'm sure is meant to explain things and it might have even made sense to you. It didnt help me at all.

It's a good doco of how they work but I guess the difficulty for me is understanding 'superposition' and how stuff can have the value of 0 and 1 lol? either its 0 or 1 right, not both?



last edited by gamer at 13:27:38 14/Dec/09

thread title typwned imo

Well, to directly answer your question, they are good because they operate in a fundamentally different way to regular computers that allows them, in theory, to perform certain operations much much faster.

They are fast because (very abstract and using what I believe is the definition of a "perfect" quantum computer) they are able to hold all the "answer space" in one single computation and derive the "correct" answer from that, where a normal computer has to do them all in sequence.

It wasn't a jab on the chin; your question is extremely broad and thus can be answered by half-assed comments like mine above which don't really answer anything. If you're specific about what you do and don't understand then maybe people can step in and offer some more insight. No need to whine about it.

It's a good doco of how they work but I guess the difficulty for me is understanding 'superposition' and how stuff can have the value of 0 and 1 lol? either its 0 or 1 right, not both?

Yeh I think that primer is less of a good explanation than wiki: "A single qubit can represent a one, a zero, or, crucially, any quantum superposition of these". There are no values "between" the zero and the one; it's just that the superposition means the values are zero and one /at the same time/ and thus the outcomes that eventuate are based on the quantum computer being able to interpret all those values at the same time

Wow Jim, thats fantastic you know what wikipedia is, well done old timer.

half-assed comments like mine above which don't really answer anything.

Well you said it best there. Your last responce though was alot better, thanks. You can call it winging all youw ant Trog but in the end all your doing is posting in a thread that you have no interest in and for some reason taking that out on me, if you dont like the thread or dont have interst in it, dont post.

Thats the quickest way to have it fall down the threadlist. I think its interesting and i'm sure some really head trippy stuff can be explained by some people that also take interst in it.

There are no values "between" the zero and the one; it's just that the superposition means the values are zero and one /at the same time/ and thus the outcomes that eventuate are based on the quantum computer being able to interpret all those values at the same time

Cheers for that. Owie! That makes my head hurt.

So that leads onto, how the hell would you get computation from stuff like that? In our computers we have 1's or 0's and therefore are able to work with binary addition for example, but if the bit your storing your temp calulation in can change or contain either value wouldnt that mean your output might be skewed? How to you balance/calibrate/check for that?

Maybe im still not understanding it correctly though...

last edited by gamer at 13:44:52 14/Dec/09

An example of what I mean with the last question is the below

in our computesr today where we have two lots of bits to use (hypothetically...) to do a calculation named aa and bb...

you want to see what 1 + 1 is equal to (using lame binary example here but stay with me...)

you would have aa=01 and bb=01

01
01+
---
=10 (2)

Thats great, we all should understand that and how binary makes that work etc.

But when you talk quantum arnt you talking about having something like this have a possibility of happening?

01
01+
=11 (3)

because aa or bb might be two things at the same time or change? without control over those bits so that they stay the same value how could you compute with them?

(i'm already facepalming myself for my own ignorance so i thank anyone ahead of time that might want to try and explain this to me)

Okay I read up on that operations link... out of the two paragrpahs all i really got was

however by repeatedly initializing, running and measuring the quantum computer, the probability of getting the correct answer can be increased.

so they run 1+1 = 2 say 100 times and they get something like

1+1=0 (5%)
1+1=2 (90%)
1+1=3 (5%)

and take the one with the highest probability?

Man thats awsome.

what I'm NOT interested in is threads that violate the rules by asking things that can be determined from a simple Google.

I know we've got two lines of discussion going with this and i'm not interested in continue this line anymore then you are but I did want to say that if it was 'easy' for me to google and find the answer to this dont you think I already would have? (im _really_ not trying to piss you off with this reply, just wanted to explain myself!)

I brought it here because of two reasons, 1, some people might not be aware of quantum computing and this might enlighten them, just has it has me and 2, some eliments, despite the vastness of google arnt explained in 'layments' terms enough for me myself to understand and i need to bounce it off a few people. I hardly think thats a violation of your rules. Thats the last i have on that line of discussion though. (lol at your quantum reference in relation to timelines etc)

Well, at the moment it takes the entire thing, then has a guess.

They're just trying to make it so that it guesses correct, most of the time.

I thought a link that explained exactly what you were asking might be useful
but I should've known better, cos it's you

(Thats a great link Plasma, cheers)

yeh it's the 2nd link you get when you google "quantum computers"

Google is already experimenting with using Quantum algorithm to optimise their image search.

Very interesting indeed.

ye old grover's algorithm eh?

How does qubit addition work fundamentally? How does the computer "find a result" or "input values". Do they use a laser? or a detector? or some frequency based electronics which would ultimately reduce the Quantum-ness to a classical speed limitation?

pretty much all your questions can be answered by reading the first link in the OP or some of the 'Developments' links from the wiki page :P

^
The problem is quantum mechanics. The s*** is just f***ed up.

I did first year physics at Uni, they drop relativity on you after nice and simple Newtonian physics, you finally get your head around that s***, work out all the f***ed up s*** that they tell you light does and then BANG QUANTUM MECHANICS FATALITY.

last edited by Hogfather at 20:14:21 14/Dec/09

the age old cat in a box but improved for quantum physics

Sorry to say that link is not very helpful.

Think of it as an indicator, if you understand the cat analogy you have some vague idea of quantum physics is on about, if you don't you have absolutely no idea.

Wait till you read about "imaginary time" and string theory.

Quantum mechanics explains why light is a particle and an energy wave... and goes on to say all matter and energy can be both.
It says nothing can ever reach absolute 0.
And it says things can be created from nothing (Uncertainty Principle ... its like a Terry Pratchett novel)

It's like science fiction for scientists. I have read a little bit of it things like A Briefer History of Time by Hawkings and Introduction to Quantum Mechanics by Griffiths, the first I could atleast get. The second was very very dry, loads of maths and seemed to have loads of implied knowledge.

At which point I decided much like the cat, is it there, is not there, did the poison, hammer, or radiation kill it, does it matter ?

the trick becomes how to look for an answer/state

I think the answer is supposed to be the state that has the least energy for algorithm's inputs?





So when Quantum computing gets to the point of being able to crack encyption, it will also be used to create it, so we will be in the same boat.

There will be tricks that force the 'answer space' to collapse into a 'wrong' answer 99.99% of the time and you will have to know the exact probability of the answer that you want.

Or something like that.

if you could somehow tell if a superimposed state satisfied a condition you could solve a lot of problems in log n time.