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Computers That Solve Problems Without Being On
Iron Monkey writes: "Nature has this article about how quantum computers can theoretically solve problems without ever actually being turned on! Maybe California can use a few of these to solve their energy crisis - the ultimate in conservation."
Big deal. Take Ye Olde Quantum Two slit experiment. Cover one slit. The interference pattern disappears. Is that "counterfactual" or simple wave mechanics? Of course the particle doesn't need to hit the bomb; its wavetrain will, and create the interference whether the particle goes one way or another.
The obfuscation just kills me. It seems the more contorted the interpretation, the more likely it is to be published.
---- "If we have to go on with these damned quantum jumps, then I'm sorry that I ever got involved" - Erwin Schrodinger
The point is that this beam splitter arrangement is a simple interferometer. When the bomb is a dud, its mirror does not "measure" (interact destructively with) the photon wavetrain, so the interference pattern persists. If the bomb is set up to measure the photon, the interference pattern disappears. This is about the first thing people tried with the two-slit experiment.
Hence my question: is this configuration considered publishable? It's a no-brainer. It has no new physics, and adds nothing to the interpretation. It's a simple retelling of the old two-slit experiment, and it coins a new obfuscatory word to boot.
Here's my "counterfactual" experiment:
Set up two slits. Put a bomb with a (transparent) electron detector trigger over one of the slits. Do the two-slit experiment. If the bomb is a dud, the detector will not interact with the particles' de Broglie waves, and an interference pattern will appear. If the bomb is not a dud, the interference pattern will disappear (or the bomb will go off).
For each electron going through the apparatus, you have the same 50/50 chance of detonation if the detector is working. It's harder to measure the interference pattern, since you need more than one electron, but the mechanics are the same. You still have a non-zero chance of finding that the detector is working without activating it (if all the electrons go through the other slit, and you get enough to see that the interference pattern isn't there).
---- "If we have to go on with these damned quantum jumps, then I'm sorry that I ever got involved" - Erwin Schrodinger
The same way a radio picks the "right" frequency out of all possible frequencies. An apparatus is set up which reinforces certain (De Broglie) wave patterns while allowing others to cancel out. When a stable wave pattern arises, the "answer" is embedded in the amplitudes at various spots.
Think of it as a very complicated resonator, which settles very quickly into a stable pattern of motion.
---- "If we have to go on with these damned quantum jumps, then I'm sorry that I ever got involved" - Erwin Schrodinger
Unfortunately most people don't understand that everything that's not measurable is religion.
Einstein mainly objected to the idea that QM, which is a form of statistical mechanics, is proof that the universe is inherently statistical and non-deterministic. While there's no reason why it couldn't be, there's nothing in QM to sway things one way or another.
---- "If we have to go on with these damned quantum jumps, then I'm sorry that I ever got involved" - Erwin Schrodinger
Yes, you've grasped the essentials of quantum philosophy - making statements about things which can't be observed. "Superposition of states" is just a fancy way of saying we don't know (and can't know) which state it's in between interactions. It doesn't mean that reality is that way.
---- "If we have to go on with these damned quantum jumps, then I'm sorry that I ever got involved" - Erwin Schrodinger
Then your algorithm/program is wrong, just like with conventional computers. From what I have gathered about quantum computing, the trick is to find an algorithm that will give the correct solution (or one of a set of correct solutions) with the propability 1 and 0 for all incorrect ones.
Okay. Let's see if I understand this correctly.
They're saying that because any quantum state in the computer can be reduced to the null state, an answer can be found before the computation is made. In other words, the quantum state you must input into the computer to program a calculation can instead be used to predict the answer.
If you know how to program a quantum computer, you theoretically can already know what the answer is.
Now, it may take more effort to derive the answer from the input states than to just plug it into the computer and let it churn away. So the computer itself will probably not be superfluous. But it's still an interesting theorem. It seems to be saying that programming a quantum computer will be approximately as difficult as solving the problem you want to program!
Genocide Man -- Life is funny. Death is funnier. Mass murder can be hilarious.
2001-05-02 17:56:53 Computing with the computer turned off. (articles,news) (rejected)
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Can someone please explain to me how a quantum computer is made to pick a *right* answer out of all possible answers?
-jr
The only title of honor that a tyrant can grant is "Enemy of the State."
a computer turned off and solving problems.
My computer is off, and solves the problem of my backdoor falling closed.
Also, a computer that's turned off, and dropped from the empire state building on pauly shore's head solves a LOT of problems.
//rdj
No one can understand the truth until he drinks of coffee's frothy goodness.
--Sheikh Abd-Al-Kadir, 1587
Is a quantum computer that doesn't even have to be built to extract results from worlds where it was built and did run.
Although there might be minor limitations. But better not mention them, to avoid confusing the readers of nature. One of those limitations might even be, that you have to solve the problem (by whatever means) just to know how to extract and interpret the information.
The question is, does that quantum computer to be built and run in another world have to appear on a budget in this world, and where the money actually goes. But that will only be solved by quantum accounting.
"By the way if anyone here is in advertising or marketing... kill yourself." -- Bill Hicks
It isn't that a QC couldn't conveivably replace your desktop -- while it currently doesn't look feasable, a QC can emulate anything a classical computer can do.
However, there are some things that a QC doesn't do any better than a classical computer. In fact, most things, a classical computer does just as well as a QC. So the likelyhood of ever wanting to replace your computer with a QC is pretty small.
QCs have some real downsides that make implementing a general purpose one impractical or expensive. For one things, because of the no-cloning theorem (which states that you can't duplicate a quantum state without destroying the orignial), you cannot do a fan-out (connect one gate output to several gate inputs). There are ways around this, but I doubt it will ever be worth it.
Note that a classical computer is one that implements a turing machine, and a quantum computer is one that has a time-evolution operator given by the Schroding equation. "classical computers" implemented with silicon are obviously quantum mechanical devices. Classical computers will eventually have to face the quantum indeterminism of the extremely small scale, but they will still be classical comptuers -- even if they aren't implemented as silicon based semiconductors.
So does this mean if nobody looks at a Windows Box, it's got both UPTIME -AND- DOWNTIME?
Schrödinger 95, 98, 98SE, and ME. Going Down in TRUE RANDOM FASHION since day one!
"Everything you know is wrong. (And stupid.)"
"Everything you know is wrong. (And stupid.)"
Moderation Totals: Wrong=2, Stupid=3, Total=5.
Does this mean it's already done I Think Therefore I Am and got as far as deducing the existence of rice pudding and income tax before anyone managed to turn it off?
Smegma.
It's better than that: Nature summarise an article, then /. gives us a precis of the Nature article. According to the abstract of the original article, 'one can discover the outcome of [a] computation [...] without running the computer', and, of course, 'there are some limits on the information that can be obtained from them'.
Nature seems to have turned this into 'it should be possible to determine the outcome of a computation while the machine stays off', and not told us anything about what the limits are.
May be the Nature reporter didn't want to observe the original article for fear of collapsing its waveform.
It would be dead handy if they could extend their research to show that you don't even have to build the quantum computer in the first place. Hey, you probably didn't even need to know the results of the calculation, do you?
-- Andrem
There has been a major scientific break-in
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-- SIGFPE
preprint. It gives a pretty good account and should be comprehensible by somone who's done even a basic QM course - ie. it uses no fancy schmancy mathematics. Mod the parent up. Or read it here: Counterfactual COmputation
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-- SIGFPE
Reading that article while bored and revising for exams is not a good idea. My brain has switched off for the next few hours, which may impede my revision process. Although, there's probably a superstate in which I have both passed and failed my exams already, so does it really matter?
Can we get a "-1 Wrong" moderation option?
Extreme Programming for Quantum Computers:
Sounds a bit like that story about a chinese village, in which every inhabitant earns his money by doing no work besides doing the neighbor's laundry.
I wonder if that will be the eventual effect of quantum computing. Think about it. Currently all sorts of things that happen in our lives and determin the course of history flow through computers. Votes, Communication, work schedules, Weather forcasts ect. ect. ect. This trend continues with computerss for the next 50 years at which time quantum computers are/become the norm. So at that point everything from the train arriving on time to if this comp-country goes to war is worked out on a computer. Then someone gets the bright idea to look outside of a window and finds the exact co-ordinates of a passing pigeon. Since all the Quantum computers are tied together by the Internet 3 all probability waveforms collapse and the future of the universe is set in stone from that point foward.
Before you flame yes I know that Quantum computing doesn't work like this. Still it is a good thoght experiment. Might make a good short story by an Author who may or may not be alive. (Dick perhaps ;)
Pithy, yet ultimately meaningless, phrase expressed with gusto!
Hell, even Einstein didn't buy it. He said, "God does not play dice with the universe."
Just because Einstein was brilliant doesn't mean he wasn't an idiot.
I've always get riled when people point to Einstein and say, "See, if Albert E. says it then it must be true."
Yes he made revolutionary contributions to Physics based on his ability to comprehend, categorize, and summarize work by previous Physicists in a way that even highschool students can understand, fundamentally. Relatvity permanently tweaked human cognitive faculties; he evolved human's thought process.
However, he still was a religious man, which is more psychological than scientific. I hardly think that refuting a promising, revolutionary discipline, such as QM, simply because of Einstein's deeply rooted fear of the unknown is absurd. We all know it's easier to solve problems in a petri dish than it is to solve problems in your personal life, that's why Albert E. abandoned his wife and kids for his first cousin! (And if I remember correctly, one son renounced him and the other went nuts. So is it OK to abuse your family if you're a genius?)
Even the smartest among us still try to put the religious blinders back on again. It's my job to call them on it. Sorry tb3, I'm not directing this at you, I'm just ranting.
-S
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https://www.accountkiller.com/removal-requested
A simplistic comment to be sure, but the article also touches on the clasic example of Schrödinger's cat: Certainly one of the more trotesque example of quantum mechanics, out there, but I guess the value is you'll never forget it. I guess that makes a difference
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> Einstein's concept of relative time and all this quantum religion
...and...
> are both offensive to anyone who has the guts to think by themselves.
> fundamentally abhorrent ideas such as quantum mechanical tunneling
> or particle-wave duality do not even deserve to be commented on.
Newtonian mechanics state that barrier tunneling is impossible as a phenomenon, and Maxwell's stuff doesn't touch on it. This idea developed from Einstein's GR theory. Understanding barrier tunneling allowed for the eventual discovery of materials that allow barrier tunneling in predictable ways. When these materials allow the tunneling specifically of electrons, they are labelled semiconductors. These materials can be made into computing machines that allow you to post a message to Slashdot saying that the theory that decribes their behavior is bunk.
There, now, don't you feel dumb?
There is little "common sense" in modern physics, but that's only because the sense you decribe as "common" is based on macroscopic observation, and these rules break down badly as you go to extremes of smallness, or bigness, or fastness, or farness. If you push two big magnet "North" poles together, they push apart, even when they're touching. Push two protons together, however, and after they get within a certain distance, they attract each other. Abhorrent? Perhaps. Impossible? Tell the residents of Hiroshima that it's impossible.
Virg
My bad. I was so into my response that I let that by. I hereby accept 5 swats with Schroedinger's Cat.
Virg
My .02,
My .02,
zencode
iactivist.org/jason
How about doing calculations on a quantum computer that doesn't actually have to be built?
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Technoli
Juno must be drooling over these quantum computers!
The "quantum computer" they're talking about isn't analagous to a PC, and may never be. As I understand the state of the technology today, a quantum computer would have to be purposefully built to solve a single problem, but once constructed, could solve the problem without actually examining the data. See this article about quantum bomb detection - it give an easier to understand example that describes the physics behind "conterfactual computation".
Help find a cure for Gidget.
The White House said: White House spokesman Ari Fleischer was adamant Monday when asked whether the president would ask Americans to stop using so much energy.
"The president believes that it's an American way of life, that it should be the goal of policy-makers to protect the American way of life. The American way of life is a blessed one."
Wow. Let's see here...since Roe V. Wade abortion has also been an "American way of life," but I don't see him doing anything to protect it. Blessed my ass...
That just pisses me off when bone-headed leaders like Dubby can't figure out that change happens and that even "The American Way of Life" needs to change sometimes...
I've been using a similar method, alternately turning on and turning on my machine, to solve many daily tasks. For example, when I'm responding to a post-
"When I was young, we didn't have any o those sissy objects and icons. We had only zeroes and ones. My first assignment was a database management program, and I had to use only zeroes."
"You had zeroes? We had to use the letter 'O'."
Seriously speaking, how would the user know what was the problem he got the answer for? Maybe they would get 'segmentation fault, zeroes dumped' on every problem.
Just by meditating deeply enough, I should get Quake running on this mother any minute now!
sig sig sputnik
Thanks, now I have this even more surreal Blue Man Group thing stuck in my head. (They keep popping in and out of existence not in time to the beat.)
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www.lucernesys.comHorizon: Calendar-based personal finance
Hell, even Einstein didn't buy it. He said, "God does not play dice with the universe."
I can't even point you to a good introductory source, off-hand. All my textbooks were very dry reading.
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www.lucernesys.comHorizon: Calendar-based personal finance
Really? There is such a thing as a persistent current. Not that this has anything to do with the story...
First, I'd like to point out that quantum computation and quantum encryption are two almost completely separate concepts. Quantum encryption is based on the fact that quantum states cannot be measured without altering. The most common example is the polarization of a photon, but it will work for any quantum state, so long as there exist, effectively, two unique states that can transmit the data.
Quantum computation, however, is much more complex and much more interesting. Quantum computers are based on the concept of quantum entanglement, the ability of a quantum state to exist in a superposition of all of its mutually exclusive states: It's a 1 and a 0. However, this is not as easy to use as one might think. While it's true that if you have n quantum logic gates you have the ability to input 2^n data values simultaneously (as opposed to only 1 piece of data if you have n digital logic gates), this is not going to be the end of classical computing for a few reasons. First, quantum computers have to be perfectly reversible. That means for every output there's an input and vice versa. And there has to be no way of knowing the initial states of the data. You don't process data, you process probabilities in a quantum computer; if you know exactly what any one value is throughout the computation, you can find out all of the values: the superposition ends and you're stuck with a useless chunk of machinery. This means YOU CAN ONLY GET ONE RESULT FROM ANY QUANTUM COMPUTATION, THE END RESULT. You can't see what the data in the middle is or the computer becomes useless. (Landauer's principle makes heat loss data loss. When your processor gets hot, it's losing data. If the same thing happened to a quantum computer, it wouldn't be quantum anymore.) Decoherence is what happens when you randomly lose data to the environment by design, not by choice, and the superposition ends. This is bad for Q.C. Oh, and quantum computers can only do *some* things faster, like prime factorization and discrete logarithms. Not multiplication or addition. Plus, the circuits that would do basic arithmetic would be bigger and slower than what you've currently got.
So what does this all mean? It means that quantum computers are going to provide some advantages (real quick big number factorization), and some disadvantages (that whole RSA standard). The most realistic initial use of quantum computers will be as add-ons to existing super-computers to resolve certain types of NP-Complete headaches that regular math can't simplify yet. At best they will someday be an add-on to your PC; but they will never replace the digital computer.~
If you want more info, check out http://www.qubit.org, it's got some decent tutorials.
Suppose you have a bomb with a trigger on its tip, so sensitive that a single photon hitting it will make it explode. Suppose further that you have some good bombs and some duds with stuck triggers that don't move. Can you tell which bombs are good and which aren't? Well sure, just hit it with a photon and see if it blows up. But can you do it without blowing up the bomb? Yes! (Well, probabilistically yes.)
Here's how it works: shoot a laser beam through a beamsplitter, bounce the two beams off of mirrors (one of which is attached to the trigger of a bomb) which redirect the beams back into another beamsplitter, with detectors on the other side. You won't understand the setup without looking at the picture -- I will be referring to it.
A laser beam is a coherent superposition of a bunch of photons. What happens if you turn the intensity down so much that you're getting single photons out? When the photon reaches the first beamsplitter, you might think that the photon either goes one way or the other. But quantum mechanics says that the photon enters a superposition state in which there is a 50% probability that it took the upper path and a 50% probability that took the lower path -- you won't know until you collapse the wavefunction by measuring which path it went through (by putting a detector along the path or something). (I'm being vague here: it's not that it went one way but you don't know until you measure it; rather, "which way it went" is simply undefined until you measure it, and if you don't measure it then it's never defined.)
So anyway, the photon hits the first beamsplitter and enters a superposition. If the bomb is a dud (fixed mirror), then this is an ordinary interferometer. At the second beamsplitter, the two beam wavefunctions (representing a single photon) interfere with themselves to produce a state with 100% probability of being detected at B and 0% probability of being detected at A. (You can see this from symmetry: the beam enters the system horizontally and has to come out horizontally too since the apparatus is symmetric.) This is precisely what you would expect classically with wave interference, by the way. Nothing too odd.
However, suppose that the bomb isn't a dud. Then the the impact of a photon on the mirror is free to move the trigger and set off the bomb, so the bomb serves as a measuring device! If it a photon hits it, the bomb will explode, so you have definitely measured that the photon took the lower path. What happens here? Like I said, there's a 50% probability that a measuring device (such as the bomb) inserted into the lower beam will measure a photon. If that happens, the bomb will explode. But what if the photon is measured to not take that path (by virtue of the bomb not exploding)? Then with 100% probability it took the upper path. When it hits the second beamsplitter, it's just as if it hit the first beamsplitter, since there's no interference from the other beam -- we know that nothing went that way. So with 50% probability it goes to detector A, and with 50% it goes to detector B.
The upshot: if the bomb is a dud, then you will get a photon at B with 100% probability. If the bomb is good, then you get an explosion with 50% probability, a photon at A with 25% probability, and a photon at B with 25% probability.
The point: if you get any photons at A, then you know for sure that the bomb was good. But you didn't actually ever send a photon to the bomb to find out! This is a "counterfactual" -- you are obtaining information about something that never happened (a photon hitting the bomb), but could have!!
Of course, you don't have an infallible scheme. Half the time you have a good bomb your test blows it up, and half the time it doesn't you can't tell whether it was good or not (because you got a photon at B). But 25% of the good bombs are provably good (without blowing them up). It turns out you can cascade this process to make the probability of detecting a good bomb as high as you want.
This effect is known as "quantum non-demolition" and has been experimentally verified (not with real bombs of course). You can use it to measure things using photons without destroying the photons (normally a photon is destroyed whenever it interacts with something -- it is absorbed).
I am intrigued/scadalized/cooled out by the article and (therefore) don't have the background to dispute it.
..or is this based on probability of some kind of tunneling right under the potential energy hill from start point to endpoint in a finite amount of time? (And is there such a "hill" in quantum computing, forgot to ask that too).
But what about:
-energy required to set up initial values so that the answer is all zeroes
-energy required for cooling or otherwise insulating/maintaining computer during the time it will be computing and simultaneously off
-who's going to police those qubits and tell them not to cannabilize energy from that environment (and presumably return it.. oops don't want to go there)
-would you need a reservoir of energy attached to the thing so that it would be theoretically possible for the system to go up the energy hump if calculation (in other universe required it)?
-do you ever even turn a quantum computer on anyway? seems a delicate enough computer could get by without humans intentionally putting power to it
-(back to the question of energy required to set up the computer): is there not a law which requires energy to create or change information, or is this a silly misconception. If so, are they not just taking care of energy expenditures before getting to the calculation stage, leaving a lot of the actual energy goings on in the unfathomable, unaccountable finite time span of computation? Or is there something else going on?
** It seems there is something more interesting going on, but there is neither mathematical meat for the professional nor a real explanation for the layman. The Royal Society Proceedings are too briefly abstracted to get anywhere. Could someone paraphrase or post the text of those proceedings or is this going to be an exercise in frustration?
In particular what exactly are the limits to the kind of probing you can accomplish which was mentioned in that abstract?
You are completely misunderstanding and need to read the original paper rather than the nature article. The strategy in the paper is not about saving energy. Quantum computers already use zero energy because they are reversible computers. The authors are not in the least bit confused about what they mean by off but it's not surprising you are confused because the Nature article is describing things in a stupid manner to be sensationalist.
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-- SIGFPE
"Michison and Jozsa describe a scheme for probing all the possible states of a quantum computer, including that in which all the 'switches' are 'off' -- that is, in which the computer is not turned on."
Just because your register is zeroed doesn't mean the chip is off.
I'll accept that the computer is off if it's not using any energy.
Cheerio,
Link.
True, but calculating this proof will definately need one of those computers!
It took a bit of head scratching and squinting, but I did finally manage to figure out how the thing works.
It uses some of the same theory as I would expect the "quantum computer" to use. In this case, they use a bomb which has a trigger which is sensative to a single photon of light. A dud bomb will pass the photon, but a live bomb will stop it. The experiment shows how it is possible to detect, using quantum mechanics, whether a bomb is live or a dud, without actually exposing it to the photon of light, and thereby exploding it.
I'm sure this is a much simplified version of what they're planning for the computer, but it's described in terms that pretty much anyone can understand, even though it's not obvious at first.
Help find a cure for Gidget.
I always tended to solve my Windows problems by just not turning the box on.
The White House said: White House spokesman Ari Fleischer was adamant Monday when asked whether the president would ask Americans to stop using so much energy.
"The president believes that it's an American way of life, that it should be the goal of policy-makers to protect the American way of life. The American way of life is a blessed one."
I say: Iron Monkey, what are you smoking? It's UNamerican to conserve. It is my patriotic duty to be an energy hog. Who needs these new-fangled 'putin machines work'in without 'tricity?
How I wish I had a quantum girlfriend that could take care of my problems without me having to turn her on.. no foreplay necessary...
Will they come with a sticker "Infinite Monkeys Inside"?
And if you watch the screen while it's running, will this collapse the computer's state and break it?
One line blog. I hear that they're called Twitters now.
Does this machine run on software that doesn't have to be written?
Problem solved.
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Friends don't let friends use multiple inheritance.
I swear, anything that is published through Nature has to be the most questionable of all things. Unfortunately, this argument is missing the most important part of quantum computing, the collapsing of the states into the final results. Without that you end up with unknown states, which you can guess the probabilities for all the possible outcomes, which in the end makes you do the whole thing by hand anyway. Trust me, I've got plenty of quantum particles making up my body and I am the master and doing a whole lotta nothing. By their logic, I should not have failed differential equations.
Why, of course, it should be well-known that while nobody looks at a quantum computer, it can be on, off, or both, right?