# A Real Quantum Computer, can you believe it?!



## Paul Revere (Sep 15, 2007)

I don't know what this has to do with furries, but its still way cool.
dwavesys.com introduced a REAL quantum computer (they claim).
Can't you just FEEL THE POWER?  Just thinking about it gives me the tinglies.


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## Paul Revere (Sep 15, 2007)

OMFG ITS SO COOL!!


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## webkilla (Sep 15, 2007)

but.... where's the proof?


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## net-cat (Sep 15, 2007)

I'll believe it when I see it...


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## nobuyuki (Sep 15, 2007)

slashdot.org


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## Janglur (Sep 15, 2007)

Actually, quantum processors have been around for SOME time.  DNA as well.


Problem is, THEY'RE EXPONENTIALLY AND INSANELY SLOWER THAN CURRENT!  It's nothing more than a proof of concept.

We have DNA computers capable of playing chess (see wikipedia for the citation) but they take ~30 mins per move.

Quantum and DNA computers aren't expected to ever be faster than current, only capable of processing more complex instructions without using a process of elimination or other lossy techniques for coming up with answers.


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## Paul Revere (Sep 16, 2007)

I haven't heard much about DNA computers, but the concept is interesting.  That's cool that you work with them.
Maybe I jumped the gun a bit getting excited about D-wave's device.  They claim their working model to be a sort of "partial" QC, capable of executing a limited set of quantum operations, but I do think sometime in the future there will be a feasible, true QC.  Their website discusses how such a device would allow for extremely accurate realtime simulations of chemical reactions and all sorts of things.  I think I'd pay an arm and a leg for one!


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## Grimfang (Sep 16, 2007)

What is so different about a quantum computer?

I checked wiki quickly, and it looks like it's able to process quantum-ish things... but is it made out of dark matter or something freaky like that? Or is it just a computer as we know it that just processes differently?


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## Kommodore (Sep 16, 2007)

Screw wikipedia, this is where you go for all your quantum needs. 

http://www.quantiki.org/wiki/index.php/Main_Page

And the relevant article:

http://www.quantiki.org/wiki/index.php/What_is_Quantum_Computation%3F

This article is very clear, but not all inclusive. I'll summarize it but it should be read anyway.

Basically, conventional computers have a problem, they produce too much heat. The chips will eventually get to a point where they are too powerful to be cooled properly, and they will not be able to make stronger chips. Quantum computation gets around this by using the rotations of electrons or atoms to be interpreted as information. The spin is altered by a magnetic field, which produces very little heat, and provides sever other significant improvements. 

A qubit, unlike a normal bit, can store much more information at a given time. Because of the nature of quantum mechanics, a qubit can exist as 0, 1 or 01 while a classical bit is restricted to 0 or 1. This increases exponentially as the bits increase. The classical bit 101 can be expressed in eight different ways as a qubit. Essentially, a normal computer does one calculation at a time, but a quantum computer does several at a time. If I recall correctly, qm's are also networked inbetween qubits, so it oberates like a brain does, several "neurons" communicating with eachother to create a network. 

Quantum computers, given the nature of their exponential increase in computation power, will be vastly, vastly superior to conventional computers at that time. The first computer smarter than a human will be quantum. They will simply be better... when they are made.

Quantum computers have been made, in a very, very primitive stage. As it stands now, there is no 'operational' qm, just working prototypes. When they work, though, they will include things like quantum communication, possibly via entanglement, and definitely quantum encryption, which uses the uncertainty principle to protect all ur codez. 

Quantum computers will mop the fraking floor with DNA computers.


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## Paul Revere (Sep 16, 2007)

Well, I don't know much about how a QC works.  I have this book on quantum mechanics, but I still don't know enough math to actually learn it.  It still seems really interesting, though, because apparently you can do things with them that normal computers can't do.  For instance, the downside to running a computer simulation of, say, an airplane in flight is that it takes a looong time to process all that info.  I guess a QC would speed these kind of calculations up a bit.

Now here's what I *really* thought was interesting.  Scientists and writers like Stephen Hawking write books to explain quantum mechanics to people like myself who don't know the math behind it.  He explains that an atom's behavior can't be directly observed, but rather is only approximated with certain equations.  So if you were to use your computer to simulate what happens when you mix Chemical A with Chemical B, you would have to wait a while for it to perform a bunch of calculations to simulate the behavior of the particles.  But with a quantum computer, you could perform a much faster simulation by actually observing such behavior -within- the processor.  I don't know how all of that actually works, but that's how it was explained to me.  Personally, I think QC's have as big a future, and will make as many fortunes, as digital computers have made in the past half-century.


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## Grimfang (Sep 16, 2007)

Damn. That's pretty cool. Technology can be pretty fucking sweet xD

Although it's unlikely I'll ever own a quantum computer, that's really interesting.


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## Kommodore (Sep 16, 2007)

Well, from concept to creation, quantum computers are advancing at more or less the same speed as early day computers. The first computers, the very first computers, came way before the super increase in power each year we all know and love. Qm's are at the first stage right now. Once they get the basic principles down, all that would be left is to improve efficiently. 

Been re-reading the qm stuff, and found some sweet things pertaining to quantum computation.  A quantum computer works like a brain, one 'neuron' communicating with another.  The thing is, the brain needs physical connections to communicate the information, quantum computers don't. Because of quantum entanglement, one electron can be entangled with another electron, changing the information of both of them, and the need not touch eachother. One electron can communicate with another one on the other side of the computer without actually touching it in any way. And a electron can be entangled with many others electrons, potentially all of the others in a system. So, you have every electron communicating with every other electron connected instantly by non-physical means. Each electron changing the state of the other, so each electron acts like thousands of others by itself, holding all that information in the one electron. Exponential computational power much?

These figure are never super accurate, (I recall readin a universe in a nutshell, in which it was predicted that by 2007 there would be processors with 10ghz of power, which is close woth the oc'ed quad cores...) but that by 2050, your laptop should have the computational power of _trillions_ of modern day super-computers. 

Pretty sweet, I love quantum stuff, it is so unconventional.


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## Janglur (Sep 16, 2007)

Paul Revere said:
			
		

> I haven't heard much about DNA computers, but the concept is interesting.  That's cool that you work with them.
> Maybe I jumped the gun a bit getting excited about D-wave's device.  They claim their working model to be a sort of "partial" QC, capable of executing a limited set of quantum operations, but I do think sometime in the future there will be a feasible, true QC.  Their website discusses how such a device would allow for extremely accurate realtime simulations of chemical reactions and all sorts of things.  I think I'd pay an arm and a leg for one!





			
				Grimfang said:
			
		

> What is so different about a quantum computer?
> 
> I checked wiki quickly, and it looks like it's able to process quantum-ish things... but is it made out of dark matter or something freaky like that? Or is it just a computer as we know it that just processes differently?


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## Janglur (Sep 16, 2007)

Paul Revere said:
			
		

> I haven't heard much about DNA computers, but the concept is interesting.  That's cool that you work with them.
> Maybe I jumped the gun a bit getting excited about D-wave's device.  They claim their working model to be a sort of "partial" QC, capable of executing a limited set of quantum operations, but I do think sometime in the future there will be a feasible, true QC.  Their website discusses how such a device would allow for extremely accurate realtime simulations of chemical reactions and all sorts of things.  I think I'd pay an arm and a leg for one!





			
				Grimfang said:
			
		

> What is so different about a quantum computer?
> 
> I checked wiki quickly, and it looks like it's able to process quantum-ish things... but is it made out of dark matter or something freaky like that? Or is it just a computer as we know it that just processes differently?


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## webkilla (Sep 17, 2007)

ahh yes.. i remmeber Qubits - its supposedly whats going to allow for AIs to be made properly, since we'll have 1, 0 and 01 as base signals meaning yes, no and 'maybe' in a more advanced 'tertiary' (as opposed to 2-component binary) code.


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## Paul Revere (Sep 17, 2007)

Yea, I thought it was funny when I read for the first time that a qubit can answer a question with "yes", "no", or "maybe".  Heck, I still think its funny!


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## foxystallion (Nov 1, 2007)

Janglur said:
			
		

> Actually, quantum processors have been around for SOME time.  DNA as well.
> 
> 
> Problem is, THEY'RE EXPONENTIALLY AND INSANELY SLOWER THAN CURRENT!  It's nothing more than a proof of concept.
> ...



Quantum computers are not inherently slow.  Quantum logic elements have been built that work at optical frequencies.  The advantage of quantum computers is not in processing complex instructions - it is in being able to test all possible solutions to a very complex problem simultaneously.  This isn't important for running a payroll program.  This makes all the difference in the world for solving NP Complete problems, such as factoring extremely large numbers.  It is very easy to multiply two very large prime numbers together to obtain their product.  It is very difficult to start with that product and calculate the two very large prime divisors.  The difficulty of doing this increases faster than exponentially with the size of the problem when using a conventional computer.  Not so with a quantum computer.  Since many modern crypto systems are based on this asymmetry, a substantial amount of NSA and DOD money is going into quantum computer research.  The practical problem has been to maintain quantum coherence through a long chain of processing elements.  A theoretical proof that quantum coherence regeneration is possible has been published.  Our future is going to be more interesting than we can possibly imagine...


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## Paul Revere (Nov 1, 2007)

foxystallion said:
			
		

> Our future is going to be more interesting than we can possibly imagine...



That's for sure.


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## Zestence (Nov 1, 2007)

Paul Revere said:
			
		

> foxystallion said:
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im still waiting for my holographic display....


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## DragonTrew (Nov 7, 2007)

Quantum computer will need quantum programming... So forget about it for a period of time...

A normal bit based computer works with 0 or 1, a quantum one works with all the 4 states of the matter... so the programming would be 2 times more complex and the operations that this computer will be able to do will follow the laws of the quantum physics... I think... :shock:


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## Tachyon (Nov 9, 2007)

A little bit of misinformation is floating around here, so I'll see what I can do to fix it up. I'm a PhD student working in experimental quantum information using optics, FWIW. Quantum computation is a subfield of information, though my recent work is focused more on precision measurements. Anyway...

There are a lot of tricky things to quantum computation. First, any and all particles behave in a quantum mechanical way, as defined by the physical laws of this wonderful weird place we call our universe. The smaller the particles are, however, the easier it is to see this behaviour. Electrons, photons (as I use), ions, a whole range of different particle types can be used as the building blocks of quantum computational devices. Not all are equal, though. Particular particles have advantages and disadvantages. For example, ions are relatively easy to manipulate and measure, however they have problems with unwanted interactions with their environment. Photons are much easier to generate and transmit, and have practically zero environmental interactions, but that makes them relatively difficult to store and measure.

To behave in a "quatum mechanical way" means that the state of a particle (eg, its magnetic spin for electrons and ions, or its polarisation for photons) is probabalistically intertwined with how you measure it. That is, the way you measure the particle can bias the result you get. For example, measuring the polarisation of a photon is affected by the relative orientations of the measurement device (polariser) and the actual polarisation state of the photon. If the actual state is halfway between the "positive"- and "negative"-result orientations of the device, half the time you will get a positive result, and the other half of the time you will get a negative result.

Another tricky thing about quantum mechanics is that when you measure the state of a particle, the state of the particle following that will always be whatever the result said the state was, _regardless_ of what the state actually was to begin with. Taking the photon example with halfway polarisation again, the measurement would cause the photon to then be in one state (positive) or another (negative), but no longer in the halfway state.

These two tricky things lead to a third tricky thing: entanglement. This is when the state of one particle is intertwined with the state of another. Kind-of like if I were to sticky tape two coins to a stick and flip it. If I were to flip to coins separately the resulting states, heads or tails, would not be correlated at all. But if I taped them next to each other, the states would be totally correlated. In quantum mechanics there is a continuum of this correlation, and it affects the measurement probabilities I mentioned above.

(What CommodoreKitty is describing sounds to me like "cluster state computing", which is a particular approach to quantum computing, though not the only one. In it, instead of preparing particle states and using gates more like traditional computers, the particles are all entangled with each other, and measurements performed in algorithmic ways. The correlation (entanglement) between the states plus the fact that the measurement alters the state of the particles is what performs the computation.)

Moving on, the standard approach to quantum computing is to consider the "qubit". Like a regular bit it has two logical states, 0 and 1. These are the states you can measure the qubit as being in, one or the other. However, because of the aforementioned probability inherent in quantum mechanics, a qubit may actually be in a state of not 2, 3, or even 4 possible states, but an infinite number of possible states spread between 0 and 1. (And even off the real-number line, if you've ever studied complex numbers.)

Yes, an infinity of states. The states between 0 and 1 are called superposition states, because it's like being somewhat in state 0 and somewhat in state 1 at the same time! With this, you can do all sorts of cool interactions between qubits, quantum computational gates, tricks with entanglement, etc. But there's a catch: You can only measure a single qubit to be in one of the two logical states, 0 or 1, and you can't make an independent copy of a qubit. This essentially means that you can't differentiate between all the states accurately.

So what the hell good is it if you can have an infinite number of states but no way to access them all? Well, this is tricky. You have to find a way, a "quantum algorithm", that can use superposition, probabilities, entanglement and measurement in a useful way. In fact, there are only a few quantum algorithms devised so far that can use the weirdness of quantum mechanics to any advantage. Prime factorisation is one, as foxystallion mentioned. This is a poster-child for quantum computation because it has an obvious application once implemented in a working machine. Direct simulation of actual quantum mechanical processes (for chemistry, etc.) is another obvious application. Nobody is really sure how many more quantum algorithms will be developed in the future, or whether they will have application to all NP-complete problems. (I think I'm right if I say that quantum computers will not answer whether or not P=NP, for the record.) It appears, though, that quantum computers have application to problems that are suited to high parallelism but relatively few "answers", such as prime factorisation, database seaching, and some others.

So, the deal is, quantum computers will be good for certain problems and applications, but at the moment we're not really sure exactly what all those applications are. (For comparison, try asking the guys who invented the transistor (or vacuum tube) as they were researching it what applications they thought it would be useful for, and I doubt they would even come close to the ubiquity of electronics we have today.) It's even more difficult because quantum algorithms work on a different paradigm to conventional computers, so coming up with good uses is tricky. It's not as simple as being x times harder - it's just a different ball game.

We've got a way to go yet, it's early days, but it's all very exciting. We're taking the fundamental weirdness of the physical universe and making it our bitch. What's not cool about that?

I hope at least some of that made sense. Peace.


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## DragonTrew (Nov 9, 2007)

Holy mother f.... I thought it was just 4 states... but an infinity.... Definitively Quantum things are complex... Thanks very much for all that info. And I hope this new technology will not be used to do some state-of-the-art-complex calculations for a new super-duper Nuclear Bomb...


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## foxystallion (Nov 9, 2007)

Tachyon said:
			
		

> ...These two tricky things lead to a third tricky thing: entanglement. This is when the state of one particle is intertwined with the state of another. Kind-of like if I were to sticky tape two coins to a stick and flip it. If I were to flip to coins separately the resulting states, heads or tails, would not be correlated at all. But if I taped them next to each other, the states would be totally correlated. In quantum mechanics there is a continuum of this correlation, and it affects the measurement probabilities I mentioned above....
> 
> So what the hell good is it...
> Prime factorisation is one...
> ...




Thank you very much for your fine exposition. 

Your non-mathematical description of quantum entanglement is the most concise and easiest to understand that I have seen. 

The uses that you mention are of humongous economic importance, as I am sure you very well know; please tell me when it is your IPO time...  I'm serious.

Right!  We are just getting to the first De Forest triode stage (the called them "Audions")  - and no one was thinking of electronic computers yet.  The applications that we haven't thought of will be even more important.  My best guess is AI.

" We're taking the fundamental weirdness of the physical universe and making it our bitch. What's not cool about that?..."  Wow!  I love you and your attitude!! Let me know when when you want to open a breeding kennel...


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## Tachyon (Nov 9, 2007)

DragonTrew said:
			
		

> Holy mother f.... I thought it was just 4 states... but an infinity....



That's right, it's not a set number of discrete states, but a continuum. Just like there are an infinite number of numbers between 0 and 1, so too with quantum states: There are an infinite number of superposition states.

The caveat is that you can only discriminate between two states at a time. For example, say you have the "0.75" state. If you were to try and measure this, you'd have to resort to detecting either the 0 or 1 state. 75% of the time your result would say "The 1 state!", but 25% of the time your result would say "The 0 state!", just because of the relative "closeness" of the actual state (0.75) and the states you are measuring against.

(Though they don't necessarily have to be the "0" and "1" state that you measure against. But this starts getting quite complicated and even more difficult to describe without showing some maths, so I might stop there. And for anyone else in the know, I realise I'm glossing over even trickier things you can do, eg POVMs. They all have their own caveats, though.)



			
				DragonTrew said:
			
		

> Definitively Quantum things are complex... Thanks very much for all that info.



You're quite welcome. It's fun describing it to new people.



			
				DragonTrew said:
			
		

> And I hope this new technology will not be used to do some state-of-the-art-complex calculations for a new super-duper Nuclear Bomb...



I don't really see how, myself, but then, I can't claim to know all the future applications of this tech. (Besides, the code-cracking application of the quantum computer might be seen as a nefarious use in the same vein, especially in this "information age".)

The thing about science is that it is amoral. Not moral, not immoral, just amoral. The universe really doesn't care how we use its rules. The more we learn about how the universe works, the more good we can do, and the more bad we can do. Undoubtedly there will be people looking at how they can use this tech (or any tech, for that matter) to broaden their power, but then, there are plenty of others looking at how they can use it to make the world a better place. That's the trouble with technology. The same stuff that gives us such better lives can also be used to destroy us, and we have to deal with that fact ourselves. The technology itself doesn't care how it's used.


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## Tachyon (Nov 9, 2007)

foxystallion said:
			
		

> Tachyon said:
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Thank you, though I have to admit I think I stole it from my supervisor.



			
				foxystallion said:
			
		

> The uses that you mention are of humongous economic importance, as I am sure you very well know; please tell me when it is your IPO time...  I'm serious.



Well, if by IPO you mean what I think you mean, I'm just a PhD student at a university, so I don't think IPO's are going to happen anytime soon, here.



			
				foxystallion said:
			
		

> Right!  We are just getting to the first De Forest triode stage (the called them "Audions")  - and no one was thinking of electronic computers yet.  The applications that we haven't thought of will be even more important.  My best guess is AI.



I admit I had to look that up, but I think your analogy is a fair representation. AI? Possible, I suppose, but I struggle to think of how that would actually work. But I suppose we have many decades to figure that out yet.



			
				foxystallion said:
			
		

> " We're taking the fundamental weirdness of the physical universe and making it our bitch. What's not cool about that?..."  Wow!  I love you and your attitude!! Let me know when when you want to open a breeding kennel...



Hehe, thank you very much. Coming from you this means a lot.


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## DragonTrew (Nov 9, 2007)

Tachyon said:
			
		

> I don't really see how, myself, but then, I can't claim to know all the future applications of this tech. (Besides, the code-cracking application of the quantum computer might be seen as a nefarious use in the same vein, especially in this "information age".)
> 
> The thing about science is that it is amoral. Not moral, not immoral, just amoral. The universe really doesn't care how we use its rules. The more we learn about how the universe works, the more good we can do, and the more bad we can do. Undoubtedly there will be people looking at how they can use this tech (or any tech, for that matter) to broaden their power, but then, there are plenty of others looking at how they can use it to make the world a better place. That's the trouble with technology. The same stuff that gives us such better lives can also be used to destroy us, and we have to deal with that fact ourselves. The technology itself doesn't care how it's used.



Yeah, I hope it will be used with INTELLIGENCE... And there's a funny thing, actually I'm graduating on Information Systems by the University of SÃ£o Paulo here in Brazil... But when the QC comes, it will bring with it some Quantum Encriptation methods, so they will be secured for a bit longer. Otherwise the fact that a non-quantum code is easy to break (for a QC) makes me shudder...


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## foxystallion (Nov 12, 2007)

DragonTrew said:
			
		

> Yeah, I hope it will be used with INTELLIGENCE... And there's a funny thing, actually I'm graduating on Information Systems by the University of SÃ£o Paulo here in Brazil... But when the QC comes, it will bring with it some Quantum Encriptation methods, so they will be secured for a bit longer. Otherwise the fact that a non-quantum code is easy to break (for a QC) makes me shudder...



Rest easy!   Quantum encryption devices are already being manufactured and sold, but there won't be a big market for them until they are needed.

But there is a classical alternative: If quantum computers break the current encryption methods, we can simply go back to the ancient method of using a one time pad of random numbers that are XORed with the plaintext to encrypt it.  The one time pads would have to be distributed via physical means, such as on DVDs.  Tip: When this happens consider going long on UPS, FED-X, and DHL stock.  They will get a lot of new business, but it will be a minor inconvenience and expense, not the end of the cyberspace commerce world as we know it.


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## foxystallion (Nov 12, 2007)

Tachyon said:
			
		

> foxystallion said:
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IPO means what you think that it means.  Unlike most tech investors, I have great patience.  Many of my investments have a 20 year time horizon.  Whether it be 5, 10, or 20 years, I expect to still be here.


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## Oni (Nov 12, 2007)

Tachyon said:
			
		

> A little bit of misinformation is floating around here, so I'll see what I can do to fix it up. I'm a PhD student working in experimental quantum information using optics, FWIW. Quantum computation is a subfield of information, though my recent work is focused more on precision measurements. Anyway...
> 
> There are a lot of tricky things to quantum computation. First, any and all particles behave in a quantum mechanical way, as defined by the physical laws of this wonderful weird place we call our universe. The smaller the particles are, however, the easier it is to see this behaviour. Electrons, photons (as I use), ions, a whole range of different particle types can be used as the building blocks of quantum computational devices. Not all are equal, though. Particular particles have advantages and disadvantages. For example, ions are relatively easy to manipulate and measure, however they have problems with unwanted interactions with their environment. Photons are much easier to generate and transmit, and have practically zero environmental interactions, but that makes them relatively difficult to store and measure.
> 
> ...


*takes very serious notes*
*hails Tachyon*

Thank your for disclosing that information Tachyon.
That is awesome information.

Spelling check!, 
You spelled probÂ·aÂ·bilÂ·istÂ·iÂ·calÂ·ly incorrectly! What if that was a photon your were dealing with!
(I had to verify that probabilistically is a real word) hehe


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## DragonTrew (Nov 12, 2007)

foxystallion said:
			
		

> Rest easy!   Quantum encryption devices are already being manufactured and sold, but there won't be a big market for them until they are needed.
> 
> But there is a classical alternative: If quantum computers break the current encryption methods, we can simply go back to the ancient method of using a one time pad of random numbers that are XORed with the plaintext to encrypt it.  The one time pads would have to be distributed via physical means, such as on DVDs.  Tip: When this happens consider going long on UPS, FED-X, and DHL stock.  They will get a lot of new business, but it will be a minor inconvenience and expense, not the end of the cyberspace commerce world as we know it.



I think that it might not work... Why? Simply because you can put a supercomputer to find the correct combinations. Once you have the encrypted text. After that you can compare the returned text with a grammar and TADA!! you have the plain text again... (Old Turing machines already do that comparison between one text to an grammar)...

I would suggest biometrics though... I don't see how one can replicate a human bean in the exactly same way...
Or just don't store data on easy-accessible machines (lock them all in a place and no connectivity to the internet). Of course it works to non-online applications only...

Sorry for the bad English, I'm on a rush right now. no time to review the text...


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## Tachyon (Nov 13, 2007)

Oni said:
			
		

> *takes very serious notes*
> *hails Tachyon*
> 
> Thank your for disclosing that information Tachyon.
> That is awesome information.



Heh, you're welcome. And thank you for the hails, they're appreciated. XD



			
				Oni said:
			
		

> Spelling check!,
> You spelled probÂ·aÂ·bilÂ·istÂ·iÂ·calÂ·ly incorrectly! What if that was a photon your were dealing with!
> (I had to verify that probabilistically is a real word) hehe



Spelling error? Oh NO! *dies*

If that were a photon I'd probably end up having to re-take a whole set of data. Which, funnily enough, is what I'm actually going to have to do tomorrow.  *growls and grumbles...*


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## Oni (Nov 13, 2007)

Tachyon said:
			
		

> Oni said:
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I always show respect to those who have a higher intelligence level and feel the need to educate others properly and respectfully. 

Perhaps someday I'll have the same understanding of quantum things as you do. ^.^




			
				Tachyon said:
			
		

> Oni said:
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*grins a grin which hides his fangs* Hmm, interesting. ^.^ I thought photons are the smallest particles of matter we humans know of. I also did not know that we have technology which allows us to see individual photons! *thought it was all theoretical abstract stuff* ...


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## Tachyon (Nov 13, 2007)

DragonTrew said:
			
		

> I think that it might not work... Why? Simply because you can put a supercomputer to find the correct combinations. Once you have the encrypted text. After that you can compare the returned text with a grammar and TADA!! you have the plain text again... (Old Turing machines already do that comparison between one text to an grammar)...



Interesting thought, but I don't think it works. There is no pattern to a one time pad. The pad is completely random. Once a message is XOR'd with the one time pad the message has no pattern. There is no longer any discernable grammar from that encrypted message. Only if you were doing something silly like using the first few numbers of the one time pad over and over would a pattern possibly emerge. Correct use of a one time pad is uncrackable.

Or, look at it this way. If there was a way to crack a one time pad, that would mean there was a way to figure out not only what the message was, but what the one time pad itself was. But the one time pad is completely random. There is no way to know that you have the "right" one time pad - it could be anything. How would you know that you had the real message and the real one time pad used to encrypt it, and not some other incorrect message that had the same length, and corresponding pad?



			
				DragonTrew said:
			
		

> I would suggest biometrics though... I don't see how one can replicate a human bean in the exactly same way...



Well, biometrics is an identification verification technology, not encryption. Encryption technologies don't care about the guy at the other end, only the guys in the middle trying to listen in.



			
				DragonTrew said:
			
		

> Or just don't store data on easy-accessible machines (lock them all in a place and no connectivity to the internet). Of course it works to non-online applications only...



The most secure system is one that can't be accessed. It's kinda the most useless, too, unfortunately. :?


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## Tachyon (Nov 13, 2007)

Oni said:
			
		

> I always show respect to those who have a higher intelligence level and feel the need to educate others properly and respectfully.
> 
> Perhaps someday I'll have the same understanding of quantum things as you do. ^.^



I wish you good luck. It's hard to get a handle on sometimes, but it's a fascinating world. Actually _understanding_ this stuff can get tricky, though. Heck sometimes it's just easier to *avoid* trying to understand it and just trust that the maths works out.  Quantum mechanics is pretty different to the classical "bouncing billiard ball" world we live in, and has caused many a brainache.



			
				Oni said:
			
		

> *grins a grin which hides his fangs* Hmm, interesting. ^.^ I thought photons are the smallest particles of matter we humans know of. I also did not know that we have technology which allows us to see individual photons! *thought it was all theoretical abstract stuff* ...



In terms of mass you are right. Photons, the particles of light, having zero mass, are the smallest particles known. (But if you're talking actual physical dimensions, you can make arguments about wavelength such that a photon is not the smallest. Also, it's arguable whether photons constitute "matter". But I digress.)

And they're not abstract at all - they are quite real! We can indeed see individual photons; that is, we can absorb and count individual photons. In fact, my work relies on it. Peruse this for a look at the sort of device that can do it. There are some caveats, though, to do with dark noise (non 0K temperature means we sometimes get clicks when there was no photon), and efficiency (not every photon is detected), but there are tricks that you can use which ultimately mean that when you get a result you can be (100-epsilon%, where epsilon is very small) certain you had yourself a single photon.

Once you have that photon you can examine the results of whatever tricky things you tried to do to it. For example, and talking about understanding quantum mechanics, what'll really cook your noodle is to try to understand how it is that a single photon can travel through two different paths, to get from one point to another, at the same time. Referred to as "which path", not only does quantum mechanics allow this, but it's this exact sort of behaviour that's fundamental to quantum computation.

I do hope I'm not rambling now.


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## foxystallion (Nov 13, 2007)

DragonTrew said:
			
		

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A one time pad can't be cracked by a supercomputer.  Breaking the Japanese Purple cypher and the German Enigma cypher were entirely different matters - they were rotor machines, not one time pad systems.


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## DragonTrew (Nov 16, 2007)

foxystallion said:
			
		

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You're right, I thing I messed things up... Like I said I was in a rush with the university things.

It would be effective indeed, but I hope never have to use this because of the insecurity of the comp. systems... solutions tend to come, and hopefully we will live our information life in peace...


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## Summercat (Nov 20, 2007)

Whenever I have problems with the plot in my stories...

I forge on, and my characters just blame the bloody quantum.


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## feilen (Dec 3, 2007)

I was talking with my dad on this. He said that the strange thing about quantum mechanics is that if you send a request into a quantum sized bit, it takes exactly 0 nanoseconds to reply. This makes it to where if you make a computer entirely out of electron processors, it will be infinitely fast...

A great scientist once said- "_If you're not weirded out by quantum mechanics, you're not really getting what's going on._"


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## Tachyon (Dec 5, 2007)

It depends on what you mean by "send a request" and "reply". When two particles are entangled, an operation that changes the state of one will cause the state of the other to change, instantly. This is correct. This is the instantaneous part (and something Einstein himself was a bit unhappy with, this "spooky action at a distance") But the operation itself takes time. IIRC, for electrons (using their spin as the quantum state), their state is actually determined by illuminating an electron with circularly polarised light _for a specific length of time_. Change the length of time and you change the state the electron ends up in. So waiting some certain number of nanoseconds is quite crucial. Then there's making a measurement and getting the results. I'm not sure about this one, but I suspect it's a similar thing for the electron. Even if it isn't, you still have to wait for the resulting signal to propagate to your detection equipment - e.g. if it gives off light you have to wait for lightspeed (very fast, but not infinite), if it gives an electrical pulse you still have to wait for lightspeed.

If your entire machine really was a quantum computer in the purest sense, you'd need to wait for the state of all the electrons to be set before the computer runs. Once your computer is running, changing the state of electrons takes time, but the changes will be propagated between entangled electrons instantaneously. Also, if the algorithm you are running depends on the results of measurements, it has to wait for the results of the measurements to be detected before it can continue. The less trivial algorithms do. And even if not, you still need to measure it at the end, and that takes time.

Things, for the most part, don't happen instantly in a quantum computer, nor will they be able to do anything infinitely fast. The potential power of quantum computing lies (roughly speaking) in the entanglement, which lets you do some pretty funky processing, and superposition, which lets you do that funky processing on multiple values at once. Kinda like massively parallel processing. (That caveat typically being that you can only really get some sort of combined answer, not each individual answer. But I'm getting into technicalities, again.)


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## GatodeCafe (Sep 12, 2008)

A quantum computer the size of a laptop computer would have theoretical computing power of roughly the entirety of all computers on earth today.

It might just barely be able to run half life 2.


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## Pi (Sep 12, 2008)

This is only tangentially relevant, but I saw the NIST Quantum Crypto demo at DEFCON this year. It was pretty neat, they were getting 2megabits per second at 3% error rate.... over entangled photons.


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## net-cat (Sep 12, 2008)

Tangentially relevant, perhaps. But still totally awesome.

If it's true.


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