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 02-05-2004, 08:35 AM #16 wapcaplet LQ Guru   Registered: Feb 2003 Location: Colorado Springs, CO Distribution: Gentoo Posts: 2,018 Rep: I think you misunderstand the idea behind quantum computing; as mentioned, a 7-qubit quantum computer can effectively do 2^7 calculations with *one* calculation. If you had a 64-qubit quantum computer, you could do 2^64 calculations with *one* calculation. Quantum bits can be in a superposition of states - they can be both zero and one at the same time. The single calculation causes the quantum bits to "choose" zero or one, so in a way that single calculation can give you an answer that a normal computer would have to brute-force its way through all 2^64 permutations to get. Just to give you an idea how long it would take a standard computer to brute-force through 2^64 permutations, consider that it took Distributed.net 1700 days to find the answer to one 64-bit key. With classical computing, if you add another bit, it doubles the amount of time required to brute-force an answer; with a quantum computer, you just need to find a way to add one more qubit. As for waiting on previous calculations, that may be an issue, but the general idea is that a quantum computer does all of the calculations at once. And no, I wouldn't worry about them just yet, but they definitely have potential.
 02-05-2004, 07:29 PM #17 qwijibow LQ Guru   Registered: Apr 2003 Location: nottingham england Distribution: Gentoo Posts: 2,672 Original Poster Rep: ahh okay. ive done a little physics, and i understand the idea's on super position. i think the 1's and zero's are coded into spinning qbits, clockwise is one bit, anti-clickwise the other ??? but as far as my understanding goes, a 3 abit computer could be in (2^3) + 1=9 states at once. 000 001 010 ....... 111 but i wasnt told about how that would be put to use. but what you say makes sence. i was surprised at how far quantum computers have come, did you know you can download programming languages for them. cant remember any URL's though. Last edited by qwijibow; 02-05-2004 at 07:31 PM.
 02-05-2004, 07:33 PM #18 qwijibow LQ Guru   Registered: Apr 2003 Location: nottingham england Distribution: Gentoo Posts: 2,672 Original Poster Rep: Ohhh,, and i read a New Scientist Article on quantum cryptogrophy. i hear quantum cryptogrophy (using somthing to do with the particle wave duality of photons) was meant to be as touch to brute force to a quantum computer, as regular encryption is to a regular computer. but anyway, i think ive drifted far enough from the topic, hehe.
02-05-2004, 07:56 PM   #19
wapcaplet
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 Originally posted by qwijibow but anyway, i think ive drifted far enough from the topic, hehe.
You and me both

I had a university course that covered the subject a bit (no pun intended). Yeah, the bits can be encoded as spin or any other state that a quantum particle can be in. I'm not sure about how quantum cryptography would work; since you can only do the operation on a set of qubits once, I think it makes them fairly tamper-proof, since if someone tries to decrypt your message, it'll garble the message. Not sure about that though. Quantum computers could definitely change a lot of things though!

02-06-2004, 07:11 AM   #20
iainr
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 Originally posted by wapcaplet I think it makes them fairly tamper-proof, since if someone tries to decrypt your message, it'll garble the message.
This is the bit I've never understood. Surely, this makes it tamper evident, not tamper proof (someone can still mess with the message, but you'll know they've done it).

That opens up an obvious line of attack against quantum cryptography : all Eve has to do is to try to read every message. That will garble them up, forcing Alice and Bob to use a less secure communication method.

02-06-2004, 09:29 AM   #21
wapcaplet
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 Originally posted by iainr This is the bit I've never understood. Surely, this makes it tamper evident, not tamper proof (someone can still mess with the message, but you'll know they've done it)
Yeah, that's what I meant

As for the garble-every-message attack... I'm not sure how to get around that. One thing we talked about in my course was using a pair of entangled particles to send a message without actually transmitting anything: Alice and Bob each have an entangled particle. When Alice does something to the particle, it affects Bob's particle too. That may be applicable to the situation; I dunno. I know very little about quantum physics.

 02-06-2004, 10:15 AM #22 SciYro Senior Member   Registered: Oct 2003 Location: hopefully not here Distribution: Gentoo Posts: 2,038 Rep: iv done some reashear on quontoms psysics in teh past, from what i heard the quantom code is basicaly a particale taht is split into 2 particles , teh sientsts had each on do in oposite directions untill tehy wre 6 miles apart, whatever happened to 1 particle happened to teh other, only 1 problem they had, when the 1rst particle as played with in some way, the 2nd particle would react instananisouly , the scientsts 6 miles away at the2nd particle coulnt find out what has hapening to the first untill they were given a hint kinda, so its more like tranmiting half a message in relguar manner, and the other half across a whatever (sence it happens faster then lite when 1 particle is played the other particle reacts, ill call whatever its sent across, whatever ) Last edited by SciYro; 02-06-2004 at 10:17 AM.
02-06-2004, 10:19 AM   #23
wapcaplet
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 Originally posted by SciYro its more like tranmiting half a message in relguar manner, and the other half across a whatever (sence it happens fater then lite when 1 particle is played the other particle reacts, ill call whatever its sent across, whatever )
Yeah... I think the example we talked about was how to send two bits of information by only transmitting one actual bit. Alice does something to her particle, transmits 1 bit to Bob, then Bob does something to his particle and gains the second bit of information.

Complicated. I'm glad I didn't go into quantum physics, or I'd be totally lost

 02-06-2004, 11:05 AM #24 SciYro Senior Member   Registered: Oct 2003 Location: hopefully not here Distribution: Gentoo Posts: 2,038 Rep: lol its fun, only im to young to be in collage so i have to learn off the internet (like anyhting else thats important to me that i want to learn), but if ya realy wanna get confused, what if the "2 particles" were actualy only 1?, neways, to get outa topic for a sec, i wonder if it would be possbile one day that the internet was sent thru split particles, so you could have FAST internet, lol , btw does anyone know what particle they prefer to use in trying to make quantom computers?
02-07-2004, 03:10 PM   #25
iainr
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 Originally posted by SciYro from what i heard the quantom code is basicaly a particale taht is split into 2 particles , teh sientsts had each on do in oposite directions untill tehy wre 6 miles apart, whatever happened to 1 particle happened to teh other, only 1 problem they had, when the 1rst particle as played with in some way, the 2nd particle would react instananisouly , the scientsts 6 miles away at the2nd particle coulnt find out what has hapening to the first untill they were given a hint kinda
I guess this might work in theory, but I don't think it would be a very practicle implementation of quantum cryptography. All the particles have to start off together (to become entangled) before being separated; and the quantum states can't change before you want them to.

I guess the mechanism wouldn't work so well if someone had to come round every few hours to pick up more entangled particles. You might as well just tell that person the message directly really.

 02-08-2004, 08:07 AM #26 SciYro Senior Member   Registered: Oct 2003 Location: hopefully not here Distribution: Gentoo Posts: 2,038 Rep: the point of it is that its impossible for anyone to intercept the comuniacation using the 2 particles becuase whatever happens hapens much faster then light, but i dont think that u need new particles every few hours, but it is realy a intresitng thing to know, in teh future it will probly get better (or mybe somone will invent a way to travel across space imstantly (hey, if particles can do it, y cant we?)
 02-08-2004, 02:37 PM #27 wapcaplet LQ Guru   Registered: Feb 2003 Location: Colorado Springs, CO Distribution: Gentoo Posts: 2,018 Rep: They've already managed to teleport a laser beam, so it may be possible one day

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