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Defeating Heisenberg's Uncertainty Principle 160

Posted by CmdrTaco
from the schrodinger's-cat-is-next dept.
eldavojohn writes "As we strive closer and closer to quantum computing, physics may need to be improved. A paper released in Nature Physics suggests that the limit defined by Heisenberg's Uncertainty Principle can be beaten with quantum memory. From the article, 'The cadre of scientists behind the current paper realized that, by using the process of entanglement, it would be possible to essentially use two particles to figure out the complete state of one. They might even be able to measure incompatible variables like position and momentum. The measurements might not be perfectly precise, but the process could allow them to beat the limit of the uncertainty principle.' Will we find out that Heisenberg was shortsighted in limiting the power of quantum physics or will the scientists be surprised to find that such a theoretical scenario — once conducted — performs unexpectedly in Heisenberg's favor?"
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Defeating Heisenberg's Uncertainty Principle

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  • by Stooshie (993666) on Monday August 02, 2010 @10:19AM (#33109834) Journal
    1st and second post simoultaneously :-)
  • by XxtraLarGe (551297) on Monday August 02, 2010 @10:20AM (#33109846) Journal
    the uncertainty principle is in doubt.
  • EPR (Score:3, Informative)

    by ShakaUVM (157947) on Monday August 02, 2010 @10:24AM (#33109898) Homepage Journal

    Wasn't this the whole basis for the EPR paradox? Using two different measurements of location and momentum with entangled particles to build a complete state?

    If not, what am I missing?

    • But... Think about simultaneity. How do you ensure that the momentum and position were recorded at the same time? http://en.wikipedia.org/wiki/Relativity_of_simultaneity [wikipedia.org]
    • Re: (Score:3, Informative)

      by DMiax (915735)

      Yes, it was. The point being that after you do any measure your state is no more correlated and the second measure does not project the state of the first.

      I read the arxiv version of the paper (later I will have to go down to the library to get the journal one) and it seems that they simply reframe a lot of common knowledge in a different terminology. It is not like they show incompatible observables measured at the same time. Measuring position and momentum of different particles is not a problem since the

      • Re: (Score:3, Insightful)

        You are right. I know the paper well since I work in this area, and the article and summary are VERY misleading. Heisenberg's uncertainty principle is perfectly safe as originally articulated -- this is merely a rephrasing of it, and an extension of it. It is a nice paper, but I wish journalists wouldn't try to sensationalise things by saying Einstein/Newton/Heisenberg/CowboyNeal is wrong... Here, I suspect the authors are slightly to blame for this -- note the peer-reviewed article is much more conser
  • Who knows? Maybe both?

    • by Eudial (590661) on Monday August 02, 2010 @10:34AM (#33110036)

      Heisenberg's uncertainty principle is still a fundamental cornerstone in quantum physics. Incompatible observables remain incompatible. What the article says isn't that the principle is wrong, but that there is a work-around for a technical problem which the principle was causing. Much the same way the invention of airplanes did not imply gravity is wrong.

      That's all I can say without seeing some math.

      • by NevarMore (248971) on Monday August 02, 2010 @10:56AM (#33110344) Homepage Journal

        That's all I can say without seeing some math.

        2+2=5. There you've seen some math, now please continue.

      • Heisenberg's uncertainty principle is still a fundamental cornerstone in quantum physics. Incompatible observables remain incompatible. What the article says isn't that the principle is wrong, but that there is a work-around for a technical problem which the principle was causing. Much the same way the invention of airplanes did not imply gravity is wrong.

        That's all I can say without seeing some math.

        And more likely than not the Heisenberg uncertainty principle will prove to be a limit (in the mathematical sense) to the precision of the measurements just as classical mechanics can function as a limit to quantum mechanics. So, as more possible states are entangled the precision will improve but not to such a degree that it will violate the principle.

      • by DMiax (915735)
        I also would like to see the math. Too bad there is none in the paper... They just write inequalities and say "it can be violated" but the counterexample is missing. I wonder how that got out of peer review.
      • well, the summary makes it pretty clear: the theory remains the same (Heisenberg's "principle" is a very specific statement derived from the theory for a certain problem). It's just that in some pathological cases, by entangling particles, they can measure what one of them is doing (I assume they lose information about another part of the system).
        I think I heard of this before, about some laser pulses that they wanted to get some noise out of: they just split one pulse into one with less quantum noise, whil

      • by renoX (11677)

        I disagree: many thinks that Heisenberg's uncertainty principle are an aspect of 'reality', not a measurement limitation.
        My bet is that this paper has a flaw: remember that Einstein thought that quantum physics was incomplete due to the random nature of measurements and thought that the
        EPR paradox prooved this, but then experiments has shown that they agree with quantum physics and that the reality is non local..

  • by Anonymous Coward on Monday August 02, 2010 @10:28AM (#33109944)

    Why do people have to pitch stories like this as ego conflicts? If they get around the uncertainty principle, they'll be erasing it no more than classical mechanics. It's like Relativity is just a more accurate description, an improvement, a super theory on top of Newtonian physics. It doesn't 'defeat' Newton. We use his work as a valid framework all the time anyways. And when we need to go beyond it, we take up Einstein's work. Similarly, getting around the uncertainty principle won't really 'defeat' Heisenberg's work, it'll just build on it. These writers just sound stupid when they frame stories as simple binary conflicts.

    • by Anonymous Coward
      When someone sets a theoretical limit and then you outline a way to surpass that limit (in this case, predicting the outcomes for both possible choices of measurement to arbitrary precision), what would you call that if your method of surpassing that limit is sound? You would call that "building" on that limit?

      Someone assfuck the writer please

      Ah, I see you're looking for an academic discussion here.

    • by x2A (858210)

      Newton didn't say "these rules can never ever be broken, even if travelling at the speed of light".

      Einstein didn't say "These rules of relativity apply to absolutely everything no matter how big or small and you can never ever find anything that behaves differently" ... I'm pretty sure he was quite open to the idea that relativity wasn't encompassing everything.

      Heisenburg DID say that you CANNOT know these things, that they CANNOT be measured, that it actually kinda seems like you CAN.

      This is the difference

      • by vlm (69642)

        Heisenburg DID say that you CANNOT know these things, that they CANNOT be measured, that it actually kinda seems like you CAN.

        This is the difference. Newton/Einstein weren't really ruling anything out. Heisenburg kinda was. That changes how wrong they can be.

        close but not quite.

        A better way to phrase it is Heisenberg showed that you can take all the measurements you want of either individual measurement but (more or less) the standard deviation of a combined measurement is always going to be some small number, which turns out to be irrelevant for big things (cars, etc) yet comparatively huge for little things like electrons.

        Newton certainly ruled things out. Regardless of weight or density, organic or inorganic source, soul or soulless, gravity accelerates stu

        • by dylan_- (1661)

          Newton certainly ruled things out. Regardless of weight or density, organic or inorganic source, soul or soulless, gravity accelerates stuff downward around 10 m/s/s.

          I can kind of figure out what you're trying to say here, but it's just so horribly misleading that I'm going to call it Wrong.

    • On /. we need some simplifications, otherwise we don't know which laws of physics are better for us and society in general. Lets say Newton = good, contributed his laws under GPL. Heisenberg = evil, even used Mono-based calculator once. Now, we will do everything we can to make Heisenberg's work irrelevant.
    • Physics is not merely an evolutionary process; occasionally, the models are simply wrong, and must be replaced. For example, consider epicycles. For the purpose of calculation, they were adequate, if expensive. However, a simpler and better theory was found, and they were replaced entirely. Unfortunately, history has shown us that most people will bitterly defend the accepted theory, rather than consider possible alternatives.

      As Feynman once said, "If I were forced to sum up in one sentence what the Cop

  • ... but I thought entanglement meant for properties such as spin and polarisation, not position and momentum? Quite obviously 2 particles can't share the same position so measuring 1 will do you no good in finding out the position of the other but do they share momentum?

    • Re: (Score:3, Interesting)

      by ceoyoyo (59147)

      Generally entangled particles are created at the same place. For example, certain decay processes will fire off two complementary particles in opposite directions, at the same speed, in order to conserve momentum. If you measure the location of one of those particles, you know that the other must be the same distance from the origin point, in the opposite direction, so you know it's position as well.

    • by x2A (858210)

      If you can measure the direction two entangled particles are travelling, and you know they travelled in a straight line from the point they were entangled and went their seperate ways... can you triangulate? "Or something", ya know, if you have two readings, maybe you can infer a third using geometry?

    • by joeyblades (785896) on Monday August 02, 2010 @11:33AM (#33110900)

      The uncertainty principle originally made statements about what can be known about position and velocity. You cannot measure both position and velocity simultaneously above a certain degree of accuracy. The more accurate your measure of velocity, the less you know about position, and visa versa. Since most purists will hold this up as the true test of any theory wanting to refute the uncertainty principle, the theorists felt the need to suggest that this, theoretically could be invalidated, as well. Hence the mention of momentum.

      The fly in the ointment seems to be this part of the theory:

      ...maximally entangling a particle with a quantum memory, meaning all states and all degrees of freedom in the particle would be tied to all of the quantum memory's states.

      I'm not sure how many states and degrees of freedom would be required. The total is infinite for both, but perhaps these can be limited to ranges. Still the size of the quantum memory would be huge, I think. Also, there is the non-trivial trick of entangling the particle's states and degrees of freedom with the quantum memory states...

      I don't think Heisenberg will be turning over in his grave very soon...

      • by Chris Burke (6130)

        The uncertainty principle originally made statements about what can be known about position and velocity. You cannot measure both position and velocity simultaneously above a certain degree of accuracy. The more accurate your measure of velocity, the less you know about position, and visa versa.

        I thought the Uncertainty Principle was based on something more fundamental than our ability to measure, but on the ability to define momentum and position for a wave function. A wave with only one frequency has a p

        • Re: (Score:3, Informative)

          by joeyblades (785896)

          No, it was initially based on our ability to measure. This measurement uncertainty has certain implications (or, at least, seems to). It's these implications that have led some theorist to draw conclusions about the way things are based on the way they appear...

          Of course, not everyone agrees with Bohr's interpretation. Feynman was one of the first to speak up... well, at least one of the first to speak up and be heard (Feynman was no slouch). These days it's Lee Smolin and the quantum gravity crowd that

          • by Chris Burke (6130)

            Ah, I see. The argument as I heard it made a whole lot of sense based on the nature of waves... I just need to remind myself that in the modern conception that electrons and such are neither classical waves nor classical particles, but things that have some properties of both and other properties that aren't like either.

  • by Richard_at_work (517087) <richardprice&gmail,com> on Monday August 02, 2010 @10:32AM (#33110004)
    They demoed the Ferrari 458, and one of the "features" that Jeremy Clarkson highlighted was that the dash mounted display could show you either the speedo or the GPS Sat Nav, but not at the same time - my immediate thought was "Heh, someone at Ferrari has a sense of humour and knows what the Heisenbergs Uncertainty Principle is." :)
    • Re: (Score:3, Funny)

      by Chih (1284150)

      They demoed the Ferrari 458, and one of the "features" that Jeremy Clarkson highlighted was that the dash mounted display could show you either the speedo or the GPS Sat Nav, but not at the same time - my immediate thought was "Heh, someone at Ferrari has a sense of humour and knows what the Heisenbergs Uncertainty Principle is." :)

      OH GOD NO please don't show me the speedo!

    • by brasselv (1471265)

      ....clearly, no physics paper is worth its name without a proper car analogy. *g*

  • Its about time we started work on moving technology into the 25th century and beyond.

    After the "Heisenberg Compensator" I suggest we try to move forward on injectors.Dilythium

    • by Grishnakh (216268)

      No, we need to start with artificial gravity, then impulse engines, then inertial dampers, then warp drive. These are the technologies that are critically important. Deflector beams are probably also very important.

      After that, tractor beams, transporters (including Heisenberg compensators), replicators, phasers, and holodecks can be devised.

      Transporters aren't as important as the above technologies for space travel. Shuttlecraft are good enough for getting around while the main ship is in orbit.

  • ArXiv link (Score:2, Informative)

    by Anonymous Coward

    Nature:Physics is pay-for, but this appears to be the same paper on arXiv:

    http://arxiv.org/abs/0909.0950

  • Well, I let that darn Schrödinger guy cat-sit while I'm on vacation and everytime I call him, he refuses to tell me if "mittens" is dead or alive. And when I call Heisenberg, all he says is that my cat is really fat, not if it's moving. Hopefully this new discovery will help all of us pet owners who let their neighborhood physicists cat-sit.

  • While we're modifying physics, may I submit feature requests for anti-gravity and faster-than-light travel, please?

    Also, do they have a public bug tracker up yet? I think I found a division-by-zero bug involving a cat and butter, but I'm having trouble reproducing it (as I am running out of band-aids.)

  • Yesterday on the BBC during top-gear there was a review of the new Ferrari 458

    Apparently one of the LCD displays in the cockpit functions as EITHER the speedo, or the satnav. So you either know where you are, or how fast you are going.

    Looks like the Ferrari engineer in charge of the 458 cockpit was a Heisenberg fan :P

    • Re: (Score:1, Offtopic)

      by drinkypoo (153816)

      Looks like the Ferrari engineer in charge of the 458 cockpit was a Heisenberg fan :P

      You left a dupe of a highly-scored comment left ten minutes before yours. My god, it's full of dupes. Thanks for helping make slashdot grate.

  • Physics (Score:2, Informative)

    by Sevorus (1754146)

    IANAP, but I've read quite a bit over the years, and my understanding was that the uncertainty principle wasn't a limitation in our "measurements" per se, but rather how the world itself works. To take the classic example of momentum and position, for example: the problem isn't that we can't measure both the speed and position of an electron (like our tools aren't "fine" enough or something), but rather that an electron doesn't have both speed and position in the sense that we think about it. If we attemp

    • by iris-n (1276146)

      I am a physicist, and you are perfectly correct.

      Heisenberg's theorem is a very fundamental result of quantum mechanics, and its demise would have preposterous consequences.

      The problem with Nature Physics is that they try to be a journal for "broad audience". That means zero technical details, and zero chance of evaluating the paper for yourself. However, their referees are usually very serious.

      In a nutshell, TFA from Ars Technica is (-1) Troll. Pure sensationalistic bullshit. TFP from Nature Physics is stil

  • Is that the one where you don't know whether or not your will get shot for killing meth dealers that work for your boss or something?
  • Commenting on whether or not the uncertainty principal will be broken is like asking if i get enough fiber in my diet. No one knows for sure.

  • Bad choice of names? (Score:5, Informative)

    by Krokant (956646) on Monday August 02, 2010 @11:09AM (#33110544)
    For those interested, the preprint of the Nature article can be found at: http://arxiv.org/abs/0909.0950 [arxiv.org]

    However, I don't really see what the fuzz is about. What they are in fact demonstrating is a relationship between conditional von Neumann entropies, which they claim is a measure of "uncertainty" (it is in a specific meaning of the word "uncertainty"). However, there is a difference between von Neumann entropy and the variance of a physical observable as used in the Heisenberg uncertainty principle. On the other hand, if you label a physical property such as entropy "uncertainty" and demonstrate a relationship between those entropies, then you can indeed call that an "uncertainty relation" but that's just a cheap way of attracting attention.

    Also, I am not sure if it is possible to obtain the Heisenberg uncertainty relation from their equation. I would expect that, for example by entering pure, disentangled states in their equation, that Heisenberg should be recoverable (because of course, Heisenberg also applies to pure states). I don't immediately see how that can happen since the von Neumann entropy for a pure state is zero. Perhaps I am just missing something and perhaps my QM is a bit rusty :).
  • Now that we can build Heisenberg compensators?

  • ...that the limit defined by Heisenberg's Uncertainty Principle can be beaten with Heisenberg Compensators.
  • by Afty0r (263037)

    The measurements might not be perfectly precise

    Isn't that the whole point of Heisenbergs Uncertaintly Principle?

    That it's not possible to *PRECISELY* measure an attribute of something?

    We all know it's possible to measure it reasonably accurately... (otherwise we wouldn't have speeding tickets) but Heisenbergs is not about "reasonably accurate" but "absolutely accurate".

    • Re:Afty0r (Score:4, Insightful)

      by Sockatume (732728) on Monday August 02, 2010 @11:41AM (#33111008)

      The Heisenberg uncertainty principle puts a well-defined, quantitative lower limit on the certainty for certain pairs of variables. For example the uncertainty in momentum multiplied by the uncertainty in position for a particle must be greater than or equal to h/4pi. Breaking that limit would break Heisenberg, even if the results still weren't totally totally certain, accurate and precise.

      • by Sockatume (732728)

        Err, limit on the uncertainty I should say.

      • Re:Afty0r (Score:5, Informative)

        by pclminion (145572) on Monday August 02, 2010 @03:26PM (#33114356)

        For example the uncertainty in momentum multiplied by the uncertainty in position for a particle must be greater than or equal to h/4pi. Breaking that limit would break Heisenberg, even if the results still weren't totally totally certain, accurate and precise.

        Breaking that limit would break the mathematics of quantum physics, not just Heisenberg. The momentum and position wavefunctions are simply the Fourier transforms of each other. If position is precisely known, then the position function is an impulse, and the momentum function must be a wave that extends throughout all space. This is simply the nature of the Fourier transform. If the uncertainty relation between momentum and position did not hold, then it would mean that the momentum and position wavefunctions are NOT the Fourier transforms of each other, and that would mean that all of quantum mechanics is wrong.

        What's been demonstrated here is, very clearly, not that.

        • I think that about sums up the uncertainty principle in a nutshell, for those who don't know the specifics of QM.

        • by Sockatume (732728)

          I thought that the Heisenberg uncertainty principle was an expression of some of the mathematics of quantum physics. ;)

    • That it's not possible to *PRECISELY* measure an attribute of something?

      Not exactly. The Heisenberg uncertainty principle states precise inequalities that certain PAIRS of physical properties, like position and momentum, cannot simultaneously be known to arbitrary precision. You seem to be implying that any observable SINGLE quality can't be precisely known. And its not the the attribute of *something*. The principal is specifically relegated to the region of quantum phenomena. We can, and do, measure both position and velocity of objects in the macro world every day to an arbi

  • The Ars Technica article links to the paper on the Nature web site, where it's paywalled. The authors have posted the article here [arxiv.org], where you can access it without paying.

    The Ars summary is also inaccurate.

    First off, this paper does not "topple Heisenberg's uncertainty principle." If you look at the paper, equation (1) is the Heisenberg uncertainty relation, while equation (2) is a similar, but different, uncertainty relation. The paper claims to demonstrate a violation of (2), not (1). Since (1) was p

  • ... Schrödinger's cat found alive.
  • Would this have any useful implications?
    Any chance of this meaning the law of conservation of energy is flawed, for example?

  • Position: Where in space something is at a single time (t)
    Momentum: Mass * Velocity
    Velocity: Position[t2] - Position[t1]

    "Position" by definition requires "t" to be only one value, while "Velocity" (and so, momentum) by definition requires "t" to be more than one value.

    Meanwhile, "Velocity", by definition, requires that we know two Positions.

    So: how can we ever talk about velocity and a single position? Aren't the uses here mutually exclusive? Are we actually talking about certainty of velocity vs the certai

    • "Position" by definition requires "t" to be only one value, while "Velocity" (and so, momentum) by definition requires "t" to be more than one value.

      What you have described is the average velocity: v= delta r/delta t. (those are greek deltas signifying difference) There is also instantaneous velocity which is v=dr/dt. (those are partial differentials) In the average velocity, the object could be speeding up and slowing down at any given point along the trip. For the instantaneous velocity, it is a vector qu

  • Yes, no matter how this turns out, Heisenberg was as short-sighted as Newton in defining his laws.

    Oh wait, the scientific process involves making observations and improving on/revoking the results of others by based on repeated and varied control experiments? Nah.....

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