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Quantum Computing Explained! (Well, Sorta)

CmdrTaco posted more than 3 years ago | from the over-my-head dept.

Science 145

An anonymous reader writes "Valiant effort to 'explain' quantum computing over on silicon.com — covering the difference between classical computers and quantum machines."

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Weird thing about the article (5, Funny)

Anonymous Coward | more than 3 years ago | (#34027130)

You can't possibly know if the article explains quantum computing until you actually read the article.

Re:Weird thing about the article (5, Insightful)

Pojut (1027544) | more than 3 years ago | (#34027230)

But by observing the article, you're changing it. Does that mean it will explain it to you...but not to me? :)

Actually (3, Funny)

killmenow (184444) | more than 3 years ago | (#34027354)

The more precisely the article explains it to him, the less precisely it will explain it to you.

Re:Actually (1)

ardle (523599) | more than 3 years ago | (#34028144)

I believe this to be true and am sure someone somewhere has measured it (changing it in the process ;-)
What I mean is that I suspect that if we know that someone understands a subject, our default behaviour is to believe without really trying to understand. This is a useful trait (otherwise we'd all be wasting our time trying to understand the same things) - provided that the source is trustworthy.
An untrustworthy source of information is often known as a "confidence trickster". Etc.

Re:Actually (1)

Amouth (879122) | more than 3 years ago | (#34028470)

so like the rest of /. they are aiming for meh?

Re:Actually (1)

bl8n8r (649187) | more than 3 years ago | (#34029152)

However the article may be in both precise, as well as imprecise, states at the same time.

Re:Weird thing about the article (3, Funny)

ultranova (717540) | more than 3 years ago | (#34027650)

But by observing the article, you're changing it. Does that mean it will explain it to you...but not to me? :)

It means that the article's explanation is fuzzy and all over the place, however once you read it you perceive it as having collapsed into either explaining or not explaining quantum computing.

Re:Weird thing about the article (2, Funny)

dogsbreath (730413) | more than 3 years ago | (#34029234)

Forget magic. Any technology distinguishable from divine power is insufficiently advanced.

OTOH any magic, sufficiently explained, will appear to be a technology.

Re:Weird thing about the article (1, Funny)

Anonymous Coward | more than 3 years ago | (#34028156)

No. If you change it, you are violating copyright law, and that is the most powerful law in the universe, surpassing whimpy quantum laws any day.

Re:Weird thing about the article (1)

treeves (963993) | more than 3 years ago | (#34028164)

No, it means that the more you read the article, the less certain you become about quantum computing. In other words, you should read as little of it as possible, i.e standard /. procedure.

Re:Weird thing about the article (3, Funny)

fred fleenblat (463628) | more than 3 years ago | (#34027524)

I find your argument very polarizing.

Re:Weird thing about the article (1)

dogsbreath (730413) | more than 3 years ago | (#34029304)

Well.... your polarization is argumentative.

Neener neener.

Re:Weird thing about the article (2, Funny)

human-cyborg (450395) | more than 3 years ago | (#34027744)

Not exactly. Before you actually read the article, it simultaneously does and does not explain quantum computing.

The Quantum Cat (1)

skywatcher2501 (1608209) | more than 3 years ago | (#34027786)

Maybe Schrödinger's cat is hiding in there too? And if she's dead, will she be brought back to life by observing her?

Re:Weird thing about the article (1)

NicknamesAreStupid (1040118) | more than 3 years ago | (#34027826)

I did and found it to be particularly interesting.

Re:Weird thing about the article (1)

edumacator (910819) | more than 3 years ago | (#34029886)

I haven't read the article, so quantum computing is both explained and unexplained at the moment.

I'm a linux user, and I'm gay. (-1, Offtopic)

Anonymous Coward | more than 3 years ago | (#34027158)

Debian is my distro of choice.

chatty narrative (4, Insightful)

NoSleepDemon (1521253) | more than 3 years ago | (#34027200)

Interesting but the chatty narrative is really annoying and is getting in the way of the actual useful information

Re:chatty narrative (4, Funny)

geogob (569250) | more than 3 years ago | (#34027320)

But "chat" is cat in french, which is totally relevant to quantum mechanics...

Re:chatty narrative (2, Informative)

Anonymous Coward | more than 3 years ago | (#34027326)

Agreed. The chattiness simplifies some stuff towards poor wording or misrepresentation.
For example:
"Factoring massive numbers is what internet and banking security depends on, so security, financial services and military applications for quantum computers are easy to envisage."
RSA doesn't depend on factoring massive numbers. RSA depends on the fact that factoring massive numbers is computationally difficult.

Could be better.

Re:chatty narrative (1)

NoSleepDemon (1521253) | more than 3 years ago | (#34027368)

Yep I read that too and thought 'surely the introduction of quantum computing would be a massive headache for security services'.

Re:chatty narrative (2, Funny)

Pojut (1027544) | more than 3 years ago | (#34027722)

That's correct.

And don't call me Shirley.

Re:chatty narrative (1)

bigstrat2003 (1058574) | more than 3 years ago | (#34028426)

That's a close enough explanation for the layman, however. No, it's not technically correct, but neither is it worth calling them out on.

It is very annoying that sentences start... (0)

Anonymous Coward | more than 3 years ago | (#34027442)

... on one page and continue on the next.

Re:It is very annoying that sentences start... (4, Funny)

maxwell demon (590494) | more than 3 years ago | (#34027848)

The pages are entangled.

Re:It is very annoying that sentences start... (1)

hesiod (111176) | more than 3 years ago | (#34028342)

I agree. Even worse, though, is when you use the "Print Page" link to show the entire article on one page, those broken sentences still exist and are separated by blank lines.

One minor mistake (4, Interesting)

vlm (69642) | more than 3 years ago | (#34027206)

One more thing, there is a minority of scientists who believe that building a quantum computer will turn out to be out-and-out impossible.

However, if those scientists are right, the implication of not being able to build such a machine is that quantum mechanics itself, as a description of nature, is wrong. Either way, the stakes could not be higher.

One possible failure mode is the theoretical power required could exceed the light fluxs of the visible universe, that would be a bummer. Maybe in true supercomputer style, a formerly computational problem is merely converted into an I/O problem, the interface to the classical world might be too slow/imprecise/analog/noisy/random to pull useful results out of it. Nothing wrong with quantum theory at all, just not possible to interface usefully with the greater classical world.

Or the more practical engineering/accounting failure mode where it would simply be cheaper / faster / more efficient to use mass produced classical processor, possibly for any problem.

Re:One major mistake (0)

Anonymous Coward | more than 3 years ago | (#34027566)

Quantum mechanics is NOT a description of nature. It is a probability theory which predicts the outcome of future observations. You do not need to describe nature in order to predict it: you are predicting the distribution of outcomes of a lot of observations. This is exactly the same as not needing to know the physics of dice throwing in order to predict the outcome of a large number of throws.

Re:One major mistake (2, Interesting)

Bill, Shooter of Bul (629286) | more than 3 years ago | (#34027754)

All theories are really just models of the universe, some work better and tell us more about how the universe does work. Quantum mechanics does tell us many very important things about our universe. Most importantly, and confusingly for everyone first learning it, our universe is not deterministic. Unlike dice, where we could predict with absolute certainty what the outcome would be if we collected enough data about the throw, we cannot do that in the quantum world. There are no "hidden variables" that we could use to increase the accuracy of our probabilistic predictions.

See bells theorem [wikipedia.org] for more mind bending details.

Re:One major mistake (2, Interesting)

Anonymous Coward | more than 3 years ago | (#34028110)

Note that not everyone rejects hidden variables. Claiming that QM implies a non-deterministic universe because of the absence of hidden variables is in fact subtly wrong. The dominant interpretation of QM (which claims the nonexistence of hidden variables) *assumes* nondeterminism, it doesn't conclude it. You can find a complete quote on the Wikipedia page for Superdeterminism, but there was an assumption in the design of the EPR experiment that assumed non-determinism as a means of preserving the free will of the experimenters. In other words they mixed philosophy into science then got freaky weird results, and now most of their followers fail to consider the possibility of a causal link between the two.

Re:One major mistake (1)

Bill, Shooter of Bul (629286) | more than 3 years ago | (#34029682)

I find superdeterminisim to be even stranger than quantum mechanics, and too close to creationism/intelligent design to me. The answer to every question simply becomes " because that's the way God did it" Or "because that's the way the initial conditions set it up". It seems downright psuedo scientific and even more of a philosophical intrusion. I also find the lack of free will to be more mind boggling, with more bad implications in real life than quantum mechanics.

Re:One major mistake (1)

maxwell demon (590494) | more than 3 years ago | (#34028322)

There are no "hidden variables" that we could use to increase the accuracy of our probabilistic predictions.

What Bell's theorem disproves is local hidden variables. Non-local hidden variables are perfectly possible, as Bohmian mechanics proves.

Re:One major mistake (1)

DriedClexler (814907) | more than 3 years ago | (#34029090)

Yes, but "there's a signal that propogates at infinite speed and yet can't be used for communication" is a road you really don't want to go down.

Bell's theorem forces you to choose between rejecting locality and rejecting counterfactual definiteness (i.e. the idea that there is a pre-existing property that is "waiting" for our measuring to find out what it "really was" the whole time).

Re:One major mistake (1)

maxwell demon (590494) | more than 3 years ago | (#34029548)

Yes, but "there's a signal that propogates at infinite speed and yet can't be used for communication" is a road you really don't want to go down.

You're right in that I don't. Others don't mind, however, or at least they consider that the lesser evil compared to giving up a classical reality.

Also it could in principle still be an extremely high, but finite speed (it just has to be high enough that we don't hit the "non-correlation window" with significant probability in our experiments). That would, of course, imply a change to quantum mechanics (and also to relativity, because it would mean a detectable absolute frame of reference). Again, it's nothing I consider attractive, but it's not ruled out by our experiments (provided that finite speed is large enough).

Re:One major mistake (0)

Anonymous Coward | more than 3 years ago | (#34027788)

This is a rather strong assertion with essentially no backup. You probably don't actually understand quantum mechanics either, too, but you haven't said enough to belie your lack of understanding.

Re:One major mistake (1)

sexconker (1179573) | more than 3 years ago | (#34027816)

Quantum mechanics is NOT a description of nature. It is a probability theory which predicts the outcome of future observations. You do not need to describe nature in order to predict it: you are predicting the distribution of outcomes of a lot of observations. This is exactly the same as not needing to know the physics of dice throwing in order to predict the outcome of a large number of throws.

Quantum mechanics is the behavior of things at a quantum level.

Our collective models of quantum mechanics are called quantum theory.

Our best models are probabilistic. If we could violate causality and the uncertainty principle, we may very well be able to throw away the probability portion of our models. Just as how we could determine the exact outcome of a die roll if we had an accurate enough representation of the die and surrounding environment at the time of the roll.

Thank god... (2, Funny)

PmanAce (1679902) | more than 3 years ago | (#34027222)

...for the leap in the right direction!

Seen on a major job board today (5, Funny)

Anonymous Coward | more than 3 years ago | (#34027228)

From the geniuses in H.R.

Wanted:

Quantum Computer Developer.

Qualifications:

Five years in depth Quantum computing experience. Certification in Quantum Computing highly desired.
In depth knowledge of Quantum Computing principals and a proven track record of creating Quantum Computing applications.

Principals only.

Re:Seen on a major job board today (1)

NoSleepDemon (1521253) | more than 3 years ago | (#34027404)

If anyone were able to convince HR to put such a requirement on a job position, it would surely be the most awesome fail possible, and failblog would probably make a t-shirt out of it... In fact, making a t-shirt out of it whether true or false would be absolutely awesome. Somebody, go make a t-shirt out of it, I want to wear one to work and make everyone scratch their heads.

I know you're being funny but (2, Interesting)

Tekfactory (937086) | more than 3 years ago | (#34027444)

Do you remember the Google Quantum Powered Image Search
http://www.newscientist.com/article/dn18272-google-demonstrates-quantum-computer-image-search.html [newscientist.com]

Some folks have questions about D-Waves technology, but there are people at Google who have been writing applications for Quantium computers.

Re:Seen on a major job board today (1)

PatPending (953482) | more than 3 years ago | (#34027514)

Principals only.

What, no qubits? You insensitive clod!

Re:Seen on a major job board today (2, Funny)

phrackwulf (589741) | more than 3 years ago | (#34027710)

If you're from the future, do you need H1-B Visa sponsorship? Or as long as I had citizenship in the past I could apply?

Re:Seen on a major job board today (2, Funny)

leonardluen (211265) | more than 3 years ago | (#34028134)

You forgot the additional requirement "Must have cat"

Re:Seen on a major job board today (1)

Amouth (879122) | more than 3 years ago | (#34028546)

<quote><p>a proven track record of creating Quantum Computing applications</p></quote>

"a proven track record of creating scalable Quantum Computing applications"

Fixed it it for you :) sorry seemed like you where missing a buzz word in there..

Qualified candidates (0)

Anonymous Coward | more than 3 years ago | (#34029022)

Funny, but such candidates exist.

Right here at my employer (NIST), we've had groups working on quantum computers for at least the six years that I've been around. And back in grad school I knew of candidates who spent their ~5 year graduate careers studying quantum computing. So while you can't buy a quantum computer at Best Buy yet, there are at least dozens of people who actually do meet the qualifications (aside perhaps from the certification).

OT (0)

Anonymous Coward | more than 3 years ago | (#34027328)

I miss Q*bert.

Quantum Computing Help Desk (1)

abbynormal brain (1637419) | more than 3 years ago | (#34027342)

....
[Phone recording] You reached the secure communications quantum cryptography help desk. We detected that you pressed "Reset my password". This option requires a transfer to teh 8th dimension. We are now connecting you to Lord John Whorfin ...

[Lord John Whorfin] May I pass along my congratulations for your great interdimensional breakthrough. I am sure, in the miserable annals of the Earth, you will be duly enshrined. How may I help you?

Quantum Co-Processor? (1, Interesting)

Anonymous Coward | more than 3 years ago | (#34027346)

Everyone always talks about the differences between a standard computer and a Quantum computer. Graphics cards are good for floating point numbers, why can't we have a Quantum Card to handle quantum operations? Does it really have to be one or the other?

Re:Quantum Co-Processor? (1)

Vegemeister (1259976) | more than 3 years ago | (#34027466)

Because it's hard to fit a liquid helium cooling system on an expansion card.

Re:Quantum Co-Processor? (1)

nschubach (922175) | more than 3 years ago | (#34027470)

In Quantum computing, you can have both. (?)

Re:Quantum Co-Processor? (1)

maxwell demon (590494) | more than 3 years ago | (#34028106)

You cannot get the power of a large quantum computer by repeatedly running a small quantum computer, because you cannot store intermediate quantum results in classical memory. However, real applications will probably always be combinations of classical and quantum computers, because for a lot of problems quantum computers don't have an advantage over classical computers, so it would be wasteful to do those parts a classical computer can do well on a quantum computer instead. As an example, when running Shor's algorithm, you'll use a classical computer to multiply the factor candidates to see if you already got the correct factors; while a quantum computer could do it, it would just be wasteful.

Joy another paged article (1)

Xelios (822510) | more than 3 years ago | (#34027436)

Maybe I could read the whole thing at once, if I had a quantum computer?

Re:Joy another paged article (1)

countSudoku() (1047544) | more than 3 years ago | (#34027682)

Congratulations on the purchase of a Quant-U-com Q*Bert 3000 Personal Quantum Machine...

http://www.silicon.com/management/ceo-essentials/2010/10/25/quantum-computing-cheat-sheet-39746192/print/ [silicon.com]

Personally, I'll be happy with plain old computing on nano-structures or a Photon-Computer. Nothin' special, just wicked fast, all Unixy on the insides, and small enough to fit in my jeans change pocket.
http://en.wikipedia.org/wiki/Photon_computer [wikipedia.org]

Horrible (5, Insightful)

aaaaaaargh! (1150173) | more than 3 years ago | (#34027456)

Sorry to be so negative but in my opinion the article is horrible. It doesn't explain anything unless you think bad analogies and jovial metaphors help you understand things better. After having read it, I don't know a single qubit more about quantum computers than before.

Re:Horrible (0)

Anonymous Coward | more than 3 years ago | (#34027658)

I stopped when I saw it was filed under Management > CEO Essentials and it had headlines such as "Time Machines - Oh boy."

Re:Horrible (1)

countSudoku() (1047544) | more than 3 years ago | (#34027734)

The clue to this comes from the URL, note this witty passage: /ceo-essentials/

Then, you know; NOT chocked full of science. It's written for people who did not end up taking any hard sciences in school.

Re:Horrible (1)

treeves (963993) | more than 3 years ago | (#34028330)

Actually, I imagine that quite a few CEOs did take some hard science or engineering courses, at least in tech companies. Maybe I just hope that is the case. I would not expect bank or insurance company CEO's to even bother with reading an article about quantum computing, as simplified as it might be.

Re:Horrible (1)

srussia (884021) | more than 3 years ago | (#34027912)

Sorry to be so negative but in my opinion the article is horrible. It doesn't explain anything unless you think bad analogies and jovial metaphors help you understand things better. After having read it, I don't know a single qubit more about quantum computers than before.

Perhaps they should have used Comic Sans or Bodoni [slashdot.org] .

Re:Horrible (3, Informative)

noidentity (188756) | more than 3 years ago | (#34027954)

Yeah, with a 350-pixel-wide web page (yes, the entire page), and an opening like this, I can't imagine why nobody would read any further:

Time machines - oh, boy!
Steady on Sam, I love science fiction as much as the next geek but I'm not talking about Quantum Leap here. This is even more exciting than time travel. OK, so what is this quantum computing lark then? Quantum computing and quantum information processing are research efforts that seek to exploit quantum mechanical phenomena to perform tasks such as massively parallel computing. The quantum research field also encompasses quantum cryptography, which utilises quantum phenomena to guarantee secure communications.

What are these quantum phenomena you talk of?
Tsk! Clearly weren't paying attention in physics class were you? [...]

Tip to new writers: you aren't witty, you aren't funny, you aren't entertaining. Leave your antics out of the writing and cover the subject matter so well that its inherent nature will be interesting to the reader.

Re:Horrible (1)

bradgoodman (964302) | more than 3 years ago | (#34028558)

I concur. I was going to post the same. An article that actually explained something would have been great, but I knew nothing about Quantum Computing before reading it, and am no better off now.

Re:Horrible (1)

Normal Dan (1053064) | more than 3 years ago | (#34030556)

I agree as well. I've read better articles on quantum computing.
It seems no one can really explain how calculations are actually performed. They talk about qubits and how they have 3 states, but no one ever goes into how the 3rd superposition is actually of any use. It's frustrating at times. I could rant on, but I wont.

Re:Horrible (2, Interesting)

Interoperable (1651953) | more than 3 years ago | (#34029896)

Let me take a run at explaining quantum computing less awkwardly than the article.

A quantum bit (qbit) may be in a 0 state, a 1 state or any linear superposition (combination) of the two, eg. 0 + i1. When measured, the outcome of the measurement can only be 0 or 1 with the probabilities of each being governed by the ratio of contributions to the qbit from the 0 and 1 components.

One qbit can usefully encode one bit of classical information (this is the point that most articles on the subject muddle up). Entangled qbits, however, also encode information into the relationship between them. More accurately, the state of the two qbits combined cannot be described by the individual states of each qbit. The number of possible states that the combined system can occupy is greater than the number of states that two unentangled qbits (or classical bits) could occupy. In other words, N entangled qbits occupy a much larger state space than 2^N, which is the state space for N classical bits.

A quantum register containing N qbits can yield an answer with, at most, 2^N bits of classical information once measured; however, the computation itself can be performed in a state space that is much larger than 2^N, hence the dramatic increase in computational power for certain algorithms. It's difficult to come up with algorithms that exploit the large quantum state space but yield a deterministic (rather than probabilistic answer). In some cases, however, even probabilistic answers may be okay if the correctness of the solution can be verified quickly with a classical algorithm and the quantum computation re-run.

Wrong atomic picture in TFA (1)

RobertB-DC (622190) | more than 3 years ago | (#34027476)

As obvious as it may be to include a "picture" of an atom -- a Rutherford model [wikipedia.org] -- it seems terribly incorrect to use it as the primary image to be associated with a quantum-mechanical phenomenon. Though I guess it's good enough to make the article feel "science-y".

I can't help but recall Wyoh Knott, the heroine of Heinlein's "The Moon is a Harsh Mistress", who conceived of an electron as "about the size and shape of a small pea".

Re:Wrong atomic picture in TFA (2, Insightful)

blueg3 (192743) | more than 3 years ago | (#34027626)

It's also a picture of an atom that doesn't exist. Never mind that the electrons are enormous and have circular orbits. There are 2 of one kind of nucleon and 3 of the other kind, with 4 electrons that all seem to be in the same shell.

So, the two possible atoms are Lithium-5 (-1) or Helium-5 (-2). Both Lithium-5 and Helium-5 are highly unstable. Both of them should have two electrons in one shell and two in higher-energy shell. The -2 state of helium would be challenging to produce, to say the least.

Re:Wrong atomic picture in TFA (1)

glwtta (532858) | more than 3 years ago | (#34027820)

So, the two possible atoms are Lithium-5 (-1) or Helium-5 (-2). Both Lithium-5 and Helium-5 are highly unstable.

Just means they had to take the picture really quickly.

Re:Wrong atomic picture in TFA (1)

Rockoon (1252108) | more than 3 years ago | (#34030456)

You should have your geek card enlarged.

Terrible (1)

callmebill (1917294) | more than 3 years ago | (#34027490)

I tried to RTFA, but the author wants to be too cute and buddy-buddy with me. When you're trying to learn something new, little jabs and crappy jokes prevent me from getting into the learning zone. Stick with the wikipedia article.

So... (1)

cereda (1610079) | more than 3 years ago | (#34027500)

... the article is completely right and absolutely wrong at the very same time.

Help me here... (0)

Anonymous Coward | more than 3 years ago | (#34027530)

Shouldn't the possibility of instant communications be an explored issue??????

Highly recommended book (4, Informative)

AdmiralXyz (1378985) | more than 3 years ago | (#34027580)

Have to agree with the comments above, that article is pretty useless.

Coincidentally, though, at a university book sale a few weeks ago, I picked up a copy of N. David Mermin's Quantum Computer Science: An Introduction, for just $5 (seems to be about $30 on Amazon) and I can't recommend it highly enough. It's an intro to quantum computing textbook, about 200 pages, written specifically for people who have CS or math (as opposed to physics) backgrounds, and while it's almost impossible to get into the nitty-gritty of why quantum computing works without a lot of quantum mechanics esoterica, this book does a great job of explaining how it works (which is plenty complicated on it's own).

It's not a light read (it's a textbook, after all), and contains some serious math, but it's nothing someone with a college education can't handle and it really helped me understand this whole mess better than any popular news article.

Re:Highly recommended book (3, Informative)

blueg3 (192743) | more than 3 years ago | (#34027764)

Incidentally, from Mermin's website [cornell.edu] , you can download his lecture notes [cornell.edu] at no cost. The book is directly based on the lecture notes and, as far as I recall, the notes are pretty good. I took the class while he was working on the book, so all we had to work with was the lecture notes (which have since undergone some revisions), which were essentially a beta version of the book's text.

It should be reasonably understandable to someone with a good CS and mathematical background but limited physics background. (Likewise, it should be reasonably understandable to someone with a good physics background but relatively little CS.) The course was designed to be taken by both CS and physics students. I think it was fairly challenging for the Cornell CS undergrads that were in the course, but your mileage may vary.

Re:Highly recommended book (1)

onionman (975962) | more than 3 years ago | (#34028150)

Thanks to both of you (AdmiralXyz and blueg3) for posting the recommendation. I'm a mathematician who has always wanted to know more physics, so this looks like a great reference for me.

Latency... (1)

linatux (63153) | more than 3 years ago | (#34031156)

Quantum computing - very cool, but I'm more interested in the possibility of transmitting data instantly. Running synchronous replication half-way around the globe without latency problems. Nobody seems to talk much about it, but entanglement would make this possible?

After reading that explanation... (1)

digitaldc (879047) | more than 3 years ago | (#34027582)

...my brain processes became quantumly entangled.
Since quantum computing itself is partially inexplicable, and building a physical machine is currently impossible, we probably won't be seeing this in the near future unless it is on an episode of Star Trek OR if they will use it to make Wall Street trading machines faster.

Are quantum computers Turing machines? (0)

Anonymous Coward | more than 3 years ago | (#34027646)

This is a newbie question I always had. Regarding computation alone (not those "entanglement" based communication properties etc.) will quantum computers be able to do something an ideal Turing machine can't? Can one assumes they are like our existing computers, just a lot faster for some kinds of operation?

Re:Are quantum computers Turing machines? (3, Informative)

maxwell demon (590494) | more than 3 years ago | (#34028182)

The set of problems you can in principle solve with a quantum computer is exactly the same as you can solve with classical computers. The best proof of this is that you can simulate a quantum computer with a classical computer (and vice versa). However, as far as we know you cannot simulate a quantum computer on a classical computer in polynomial time.

Re:Are quantum computers Turing machines? (2, Insightful)

FrangoAssado (561740) | more than 3 years ago | (#34028276)

Quantum computers only offer better speeds; a quantum computer can always be simulated by a classical computer. However, storage and run time of the simulation grows exponentially with the size of the quantum computer being simulated, so this is not feasible in practice.

The reverse is also true. A quantum computer (when/if built) will be able to run any classical algorithm, since it's possible to implement a classical NAND gate using quantum gates. It'd be a huge waste, however, to use quantum gates this way.

Wrong description of entanglement (1)

hweimer (709734) | more than 3 years ago | (#34027664)

Unfortunately, the author does not seem to have understood the concept of entanglement. Correlations between particles (even perfect ones) are also found in classical physics as the example with the socks implies. Quantum entanglement, however, is much more subtle, and distinguishing between useful entanglement and useless classical correlations is typically a highly nontrivial tasks.

Reality less clear than even this article seems (2)

Comrade Ogilvy (1719488) | more than 3 years ago | (#34027694)

As someone with a couple physics degree, I find this stuff both exciting and confusing. Exciting because delving into such fundamental physics is creating some beautiful results. Confused because either something is wrong with my understanding of quantum mechanics (unlikely), or we are being snowed with pie-in-the-sky promises, in order to secure funding.

Entanglement for secure channels of communication I believe. Quantum "computing" in the sense we usually think of computing looks phony.

Sure, such a quantum computer, if built, could process, say, 10^50 quantum inputs simultaneously. But where does one get the 10^50 inputs? Each input is a delicate quantum-entangled state. Do I pull my 10^50 helium-cooled quantum state composition machines out of my closet? It is a promise which is can only be employed by leprechauns and unicorns.

The bottom line is, as stated by the article, quantum computers would useless for most everyday computations. Which things a quantum computer could actually be used for is clear as mud.

I would welcome a link to a technical article that is grounded in reality, proving me wrong.

Re:Reality less clear than even this article seems (1)

maxwell demon (590494) | more than 3 years ago | (#34028518)

Sure, such a quantum computer, if built, could process, say, 10^50 quantum inputs simultaneously. But where does one get the 10^50 inputs?

An equal superposition of the 2^n states of n bits is a completely separable (i.e. non-entangled) state which just has each qubit individually in an equal superposition of 0 and 1. Since no entanglement is involved, that state is almost trivial to create. It's the processing afterwards which is complicated.

Weather Prediction? (1)

Quantus347 (1220456) | more than 3 years ago | (#34027756)

So Ive always read that quantum computers excel in parallel calculations like code-breaking and such, but if its probability calculations that it are it's bread and butter, would that extend to weather prediction modeling? I'd love for the Weather service to get as good as they were in Back to the Future II, weather predictions accurate to the second.

Re:Weather Prediction? (2, Informative)

Comrade Ogilvy (1719488) | more than 3 years ago | (#34027918)

Won't happen. While better computers help to some degree and building better models helps even more, weather is fundamentally a chaotic system. There is a hard upper limit based on the quantity and accuracy of the data. An exponential increase in overall quality of data yields a linear increase in the quality of the prediction.

To make up some numbers to illustrate the point...So if we have 10^4 weather stations to have 48 hours of good accuracy, it might take 10^5 weather stations to achieve 60 hours of good accuracy, assuming that you have all the computing power you could possible want in the first place.

Re:Weather Prediction? (1)

maxwell demon (590494) | more than 3 years ago | (#34028230)

Even with the best and fastest computer you'll not get weather prediction accurate to the second. That's because weather is a chaotic system, and you'd need an insane amount of measurement data to be that accurate (and probably would have to predict human behaviour as well!)

Um, what now? (1)

glwtta (532858) | more than 3 years ago | (#34027758)

This shared state means that a change applied to one entangled object is instantly reflected by its correlated fellows - hence the massive parallel potential of a quantum computer.

Unless I missed some major recent development, modifying an entangled particle and "instantly" observing the effect on its correlated partner is precisely what you cannot do with an entangled pair. Gets into that whole pesky faster than light communication thing that makes causality not work.

Is he just conflating entanglement and quantum teleportation?

quantum biological? (1)

smoothnorman (1670542) | more than 3 years ago | (#34027804)

There is a theory, probably via Roger Penrose (or not, or both), that biological brains are so curiously different from standard computers and good at diffuse problems like pattern matching exactly because they are tapping into quantum entanglement as a material for decision making. So... build ye a quantum computer and see it stare back from the (quantum) abyss at you... (or not)

Oh no, not again! (2, Informative)

maxwell demon (590494) | more than 3 years ago | (#34027836)

From the article:

"This shared state means that a change applied to one entangled object is instantly reflected by its correlated fellows"

Why, oh why, is this nonsense repeated again and again. If you change one entangled particle, you do not change the other. For example, if you have two spins entangled in a way so that if one is measured "up" the other is measured "down" and vice versa, and you turn the one spin around (without measuring it) then you'll have an entangled state where if you measure the first spin "up" the other one is also measured "up", just as you'd expect. As long as you don't measure, there's no "spooky action at a distance" but only local changes. The "spooky action at a distance" happens at measurement (which BTW destroys the entanglement), and it's all but a given that there's indeed an action at a distance (you only need it if you want a certain type of interpretation, where basically "under the hood" the system behaves completely classical, but we don't see it because there are so-called hidden variables which we cannot determine). The point is that in an entangled state the correlation is all which is defined, and the result of local measurements are completely undefined (OK, strictly speaking this is only true for maximally entangled states, for others there's less correlation and more local information; it's basically a trade-off between the two). Now when you measure the spin of one of the particles, the value of the spin gets a defined (but random) value (up or down, in the direction you measure), and also the value of the spin of the other particle gets a defined value, which is determined by the entangled state and the result you got for the first particle, i.e. if the entangled state was "both particles have opposite, but otherwise undefined spin" then after measurement, the particles will have opposite, well-defined spin. However, since the result is random, if you have the other particle, you cannot see any difference whether the first particle has been measured or not; he will get a random result either way. Only if he gets told the measurement result of the first particle, he can predict (or, if he already measured, compare) his measurement result.

Oh, and yes, I'm working in the field of entanglement, so I know what I'm speaking about.

But I absolutely like the following statement from the article:

"Hang on, what's quantum entanglement when it's at home?
I was afraid you were going to ask."

I hope the above explanation is understandable ...

Entanglement Fail (0)

Anonymous Coward | more than 3 years ago | (#34027926)

This article commits the classic mistake of trying to describe entanglement:

This shared state means that a change applied to one entangled object is instantly reflected by its correlated fellows - hence the massive parallel potential of a quantum computer.

No, no, no, no, no! It's exactly this kind of statement that has people thinking QM means faster-than-light communication or other voodoo. But the statement itself is just flat-out not true.

Properties of particles can either be in known states, or a unknown states. Two properties in unknown states on different particles can be entangled. Any attempt to read the property or set it to a desired value will destroy any existing information already there. This includes entangled states.

With entanglement, however, you can gain information about the other particle without disturbing it.

Imagine having a pair of magical coins. When you touch them together, then the next time you flip them they will each come up on the opposite facing. But it's only good for one flip. Until either coin is flipped, both have a 50% chance of coming up either heads or tails -- it's truly random. But once one coin is flipped, then the other will be guaranteed to come up the other way. This holds true even if the coins are flipped simultaneously!

Entanglement is indeed strange, but it does not allow for the violation of causality like the quoted statement implies!

What is this? The Barbie school of quantum mech? (0)

Anonymous Coward | more than 3 years ago | (#34028074)

The only way this could condescend further to its audience is if the author had put "Tee hee! Math is hard; let's go shopping!" in one of the questions.

Still not sold (1)

petes_PoV (912422) | more than 3 years ago | (#34028136)

The article contained a little too much "future tense" for my liking. ISTR people have been talking about quantum computing, entanglement and qubits for, what?, a decade or more. Now I'm a patient man but it still seems to be couched in phrases like "we will ..." "could ..." "would ..." "... is being researched" "... is theoretically ..." . I recall back in the 60's when lasers were the wonder of the time, they got a bit of a reputation for being a solution in search of a problem - though that's obviously changed now (we've discovered the problems they can solve). So does that mean that some time in the next 50 years, we'll have quantum computers crunching massively paprallel problems, such as decrypting all our previously secure communications, manipulating all the pixels of a video feed in real-time, right off the sensor or even with an entanglement USB peripheral that takes the place of all our networking and communications systems - providing instantaneous point-to-point links between pairs of chips?

Or does it mean that none of this will come to pass? To quote the article

the average computer user probably won't have much use for a quantum computer

I'd say it's quite important to know which way our future is headed - anybody know?

Re:Still not sold (1)

FrangoAssado (561740) | more than 3 years ago | (#34029208)

So does that mean that some time in the next 50 years, we'll have quantum computers crunching massively paprallel problems, such as decrypting all our previously secure communications, manipulating all the pixels of a video feed in real-time, right off the sensor or even with an entanglement USB peripheral that takes the place of all our networking and communications systems - providing instantaneous point-to-point links between pairs of chips?

I think you're expecting way too much from quantum computing:

In 50 years we'll probably be able to decrypt all our (current) secure communications anyway, with or without quantum computers. Of course, by then we'll be using larger keys (or probably better algorithms that provide better security with smaller keys). And if quantum computers start to become feasible, we can start moving to encryption systems that cannot be broken by quantum computers (the McEliece cryptosystem is one candidate).

About "manipulating all the pixels of a video feed in real-time", I don't think quantum computers would be incredibly useful for that, at least not in the way you seem to expect it. To get a quantum speedup, you must have a very specific algorithm that computes what you want and, at the same time, makes the correct answer come out with high probability. It's certainly not a magic thing that allows you to massively parallelize any algorithm: for search, for example, it's proven that the quantum speedup is at most sqrt(n), and that's not even counting the time it takes to encode whatever data you want to search in the necessary entangled state.

The "instantaneous point-to-point link" is even worse: quantum mechanics can most certainly not transmit information instantly. Entanglement can't be directly used to transmit information; the (theoretical) best you can do is to double the capacity of a classical channel while "spending" entanglement, and that doesn't seem to be terrible useful for your example.

Re:Still not sold (1)

petes_PoV (912422) | more than 3 years ago | (#34029400)

You could well be right. However, from the sense of optimism in the article these are the sorts of things I would come to expect. If on the one hand they're making statements using words like "revolutionise" and "massively parallel" thn they've got to back 'em up!

Personally I'd say that it's still too early to say if QC will bear fruit - just we haven't yet seen any major benefits of DNA mapping (people still get cancer). It would just be nice to read a piece that wasn't trying for the hard sell, and was able to present a quiet, factual article without all the hype.

Sigh. (0)

Anonymous Coward | more than 3 years ago | (#34028580)

We're nerds; we already understand how quantum computing works. Else, what would be the use of every single article that's already been posted about it?

I've studied Quantum Computing (1)

mathimus1863 (1120437) | more than 3 years ago | (#34029070)

...and I read most of the fine article. It puts too much emphasis on quantum entanglement, which is useful for quantum cryptography, but not as important as quantum interference. It's the weird quantum states of the individual qubits that interfere with each other, that make a quantum computer. If you can figure out how to encode information into the quantum state of a qubit, and get a bunch of them to interact in a given way, you get the quantum interference to cancel out the information you don't want, and leave the information that you do want (probabilistically speaking). Unfortunately, the math and creativity needed to encode problems as such requires some truly stellar mathematical/physical thinking, and we wouldn't be having any Quantum code-monkeys like we do with classical computers.

NSA Patented It 5 Years Ago (0)

Anonymous Coward | more than 3 years ago | (#34029098)

Lies, Damned Lies, and Science Popularizations (1)

DrJimbo (594231) | more than 3 years ago | (#34029176)

YIAATP.

As others have noted, the author's explanation of entanglement is faulty. IMO the key fault (although there are others) is the implication that entanglement can be used for (perhaps super-luminal) communication.

Perhaps only a minority of scientists think building large scale quantum computers is impossible, but I think a majority of physicists think it is impossible, I certainly do. I strongly disagree with the idea that the only way building large scale quantum computers would be impossible is if quantum mechanics does not describe nature. The key stumbling block is a phenomenon known as quantum decoherence. Wojciech H. Zurek recently wrote a fairly long review paper summarizing what is known about decoherence. IMO, just as the computing power of a quantum computer increases exponentially with the number of qubits, so does the interference from quantum decoherence.

It is like the old story of how chess was invented to please a king. The king was so pleased he offered the inventor his weight in gold. The inventor asked instead for some rice. He said put a single grain of rice on the first square of the chess board, then two grains of rice on the 2nd square, four grains of rice on the 3rd square, eight grains of rice on the 4th square, etc. At first the king thought this was a paltry reward for such a great game but after trying to fulfill the request, the king got an inkling of exponential growth and had the inventor beheaded.

Finally, the author got the connection between security and factoring large numbers backwards. Banks and internet security depend on the difficulty of factoring large numbers. Large scale quantum computers could easily factor large numbers thus rendering perhaps all of our current encryption systems obsolete. I have no idea what they would be replaced with but it seems at least possible that anyone who wanted to communicate securely would need to use a quantum computer.

Minor correction (1)

DrJimbo (594231) | more than 3 years ago | (#34029314)

The review paper I was thinking of was by Maximilian Schlosshauer. It was called "Decoherence, the measurement problem, and interpretations of quantum mechanics". He has also written a book about quantum decoherence.

Re:Lies, Damned Lies, and Science Popularizations (1)

FrangoAssado (561740) | more than 3 years ago | (#34029608)

Large scale quantum computers could easily factor large numbers thus rendering perhaps all of our current encryption systems obsolete. I have no idea what they would be replaced with but it seems at least possible that anyone who wanted to communicate securely would need to use a quantum computer.

I don't think that it's likely that quantum computers (if built) will be necessary for secure communication. There are cryptosystems (check out McEliece [wikipedia.org] ) that can be run relatively fast in classical computers and are based on the difficulty of solving NP-hard problems. Quantum computers would not offer exponential speedups for these kinds of problems (that's not actually proved, but it's even more certain than P!=NP, I think).

Re:Lies, Damned Lies, and Science Popularizations (1)

DrJimbo (594231) | more than 3 years ago | (#34030064)

Thanks for the info. As I said, I had no idea what would replace current encryption schemes.

Returning to my original critique of the article, do you see any reason why banks would need quantum computers while bank customers would not?

Er, bytes? (1)

tqk (413719) | more than 3 years ago | (#34030330)

I'm not a professional scientist. I'm a CS geek. I've also only made it through page one so far.

This struck me as very underwhelming, even disappointing:

Instead of having bits, as a classical computer does, which represent either a one or a zero, a quantum computer has quantum bits - qubits - which can represent zero, one, or a superposition of both - that is, any amount of either zero and one
simultaneously. As a result, unlike a traditional computer which can only store one number in a single register at any one time, a quantum computer can store more than one.

Doesn't that mean going from bits that hold either one or zero, to bits that hold floating point values of anywhere between zero and one, containing "percentages" of the present value between 0 and 1? What's so Earth shaking about that? Those are bytes, yes?

WTF?!?

Do I understand this correctly (0)

Anonymous Coward | more than 3 years ago | (#34030414)

If you build 2 8 qbit systems you could use them as basically a wireless NIC that'd teleport the data between the cards with no wires or range limits? You could get real time data from a probe orbiting Jupiter or even further out? That is a bit mind twisting.

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