Slashdot Mirror


A Quantum Linear Equation Solver

joe writes "Aram Harrow and colleagues have just published on the arXiv a quantum algorithm for solving systems of linear equations (paper, PDF). Until now, the only quantum algorithms of practical consequence have been Shor's algorithm for prime factoring, and Feynman-inspired quantum simulation algorithms. All other algorithms either solve problems with no known practical applications, or produce only a polynomial speedup versus classical algorithms. Harrow et. al.'s algorithm provides an exponential speedup over the best-known classical algorithms. Since solving linear equations is such a common task in computational science and engineering, this algorithm makes many more important problems that currently use thousands of hours of CPU time on supercomputers amenable to significant quantum speedup. Now we just need a large-scale quantum computer. Hurry up, guys!"

171 comments

  1. Implications by Anonymous Coward · · Score: 0

    Does this mean they can solve P=NP?

    1. Re:Implications by Anonymous Coward · · Score: 0

      Only if P is known ;)

    2. Re:Implications by Anonymous Coward · · Score: 5, Funny

      Does this mean they can solve P=NP?

      Yes: N=1.

    3. Re:Implications by X0563511 · · Score: 1

      Or if P=0, in which case N can be any number.

      --
      For large sets, this will be our guide even unto death, for the LORD will work for each type of data it is applied to...
    4. Re:Implications by lenester · · Score: 5, Funny

      Oh come on, this deserves +P Funny.

    5. Re:Implications by Anonymous Coward · · Score: 0

      No, and neither does any other quantum algorithm because P=NP is a question about Turing machines and quantum computers are not equivalent to Turing machines.

    6. Re:Implications by Anonymous Coward · · Score: 1, Informative

      No. Or, not to the best of our knowledge.

      Quantum computers solve problems in BQP. We don't even know if that is any larger than BPP, the probabilistic algorithm class.

      We also do not know if there are any problems in BQP that are not in BPP; that is, we do not know if a quantum computer can solve any problems a classical computer (with a random source) can't.

      We *do* know that there are problems for which the solution with a quantum algorithm is exponentially better than any known solution with a probabilistic classical algorithm (Shor's factoring, and TFA). Since we happen to also care if a problem is solve in a day or in the age of the universe, instead of just whether the problem is solved at all, this matters a great deal.

    7. Re:Implications by Anonymous Coward · · Score: 0

      ... we actually don't know if they are equivalent or not.

    8. Re:Implications by Warped-Reality · · Score: 2, Informative

      You're both wrong. They're equivalent.

      From wikipedia:

      "A Turing machine can simulate these quantum computers, so such a quantum computer could never solve an undecidable problem like the halting problem. "

      --
      This is not the greatest sig in the world, no. This is just a tribute.
    9. Re:Implications by Anonymous Coward · · Score: 0

      Also from wikipedia:

      "The population of African elephants has tripled in the last six months."

    10. Re:Implications by Anonymous Coward · · Score: 0

      If P != 0

    11. Re:Implications by FrangoAssado · · Score: 1

      A nitpick to avoid confusion: the above comment is talking about the efficiency of computers. So, you should read

      Quantum computers solve problems in BQP.

      as "Quantum computers efficiently solve problems in BQP" (that is, by the way, the definition of BQP). Ditto for the following paragraph: "we do not know if a quantum computer can efficiently solve any problems a classical computer (with a random source) can't (solve efficiently)."

      It also seems a little nonsensical to ask if a quantum computer can solve P=NP. "P=?NP" is a mathematical question, so this is like asking if a quantum computer can prove Fermat's Last Theorem. I think the parent poster sensibly interpreted the question as "does this mean quantum computers can (efficiently) solve NP-complete problems? (That is, does BQP contain NP?)".

    12. Re:Implications by DavidShor · · Score: 1

      "so this is like asking if a quantum computer can prove Fermat's Last Theorem. "

      Any hopes for a speed-up on Automated-Theorem-Proving?

    13. Re:Implications by omuls+are+tasty · · Score: 1

      It's not a question of computability, it's a question of efficiency (time complexity).

      Nondeterministic and deterministic Turing machines are also equivalent in the power of expression, but most likely not equal in terms of time complexity (otherwise P=NP).

    14. Re:Implications by FrangoAssado · · Score: 1

      Any hopes for a speed-up on Automated-Theorem-Proving?

      Automated theorem proving (using propositional calculus) is NP-complete, so it's the same "no, to the best of our knowledge". (Using first order predicate calculus is even worse -- the algorithm is not even guaranteed to terminate).

    15. Re:Implications by Guignol · · Score: 1

      What an excellent reply !
      I don't think this is nitpicking at all, on the contrary, this is absolutely essential
      It is one thing to wonder is P=NP, another thing to not be bothered by whether it is true or not by 'magical' quantum tricks that will basicaly void the interest of the P=NP question for practical ends, and it is yet an entirely different thing to use this to conclude the original question.
      Your reply is very insightful, I got confused by the previous answer because I fell for the same trap in confusing the interest of the question with the question itself. thank you very much for putting me back in the right track, really !

  2. Hm by Andr+T. · · Score: 2, Funny
    Is this algorithm in Haskell or somethin'?

    I'll wait until I can program in VB. Will it take long?

    --

    Any life is made up of a single moment, the moment in which a man finds out, once and for all, who he is.

    1. Re:Hm by FrozenFOXX · · Score: 5, Funny

      Is this algorithm in Haskell or somethin'?

      I'll wait until I can program in VB. Will it take long?

      It may or may not.

      --
      "Just a fox, a whisper."
    2. Re:Hm by Anonymous Coward · · Score: 3, Funny

      Following the protocol of quantum physicists to be un-understandable by anyone but the top people in their field and 13-year-olds with too much time who watch NOVA and read Popular Science, they wrote it in Perl

    3. Re:Hm by AdmiralXyz · · Score: 5, Funny

      Quantum computing is nondeterministic and probability-based: when you put in a certain input, you have a finite probability of getting the right answer out, it could just as easily be anything else. So in other words, coming from VB, you'll be at a major advantage.

      --
      Dislike the Electoral College? Lobby your state to join the National Popular Vote Interstate Compact.
    4. Re:Hm by Anonymous Coward · · Score: 2, Funny

      Also, it may AND may not.

    5. Re:Hm by Arthur+Grumbine · · Score: 1

      Following the protocol of quantum physicists to be un-understandable...

      "Derstandable"!?
      That word is incomprehensible to me. I am unable to understand it, is what I'm trying to get at...y'know: baffling, beyond comprehension, clear as mud, cryptic, Delphic, enigmatic, fathomless, Greek, impenetrable, incognizable, inconceivable, inscrutable, mysterious, mystifying, obscure, opaque, perplexing, puzzling, sibylline, unclear, unfathomable, ungraspable, unimaginable, unintelligible, unknowable.

      --
      Now that I think about it, I'm pretty sure everything I just said is completely wrong.
    6. Re:Hm by Hercynium · · Score: 2, Informative

      This was solved in Perl a long time ago.

      No, really!!

      Quantum::Superpositions

      --
      I'm done with sigs. Sigs are lame.
    7. Re:Hm by Nethemas+the+Great · · Score: 1

      Sure it might "help" VB but just think of the possibilities with PHP...

      $numberClueless = "0";
      if(empty($numberClueless)) print("Yay for PHP");

      --
      Two of my imaginary friends reproduced once ... with negative results.
    8. Re:Hm by mikael · · Score: 1

      And used a Brownian Motion generator using a fresh cup of really hot tea..

      --
      Vintage computer adverts: http://www.vintageadbrowser.com/computers-and-software-ads
    9. Re:Hm by p!ngu · · Score: 1

      The joke is that "un-understandable" is funny. He's not being serious, obviously.

  3. Seems bogus by Anonymous Coward · · Score: 0

    Uh, in O(log n) time their algorithm can't even read all the input. Maybe they meant to compare parallel quantum vs parallel classical?

    1. Re:Seems bogus by Anonymous Coward · · Score: 4, Insightful

      Maybe you should READ the damn thing and notice how that's addressed in the first half-page.

    2. Re:Seems bogus by Bitch-Face+Jones · · Score: 4, Funny

      In O(log n) time he can't read the entire article.

    3. Re:Seems bogus by mesterha · · Score: 1

      Uh, in O(log n) time their algorithm can't even read all the input. Maybe they meant to compare parallel quantum vs parallel classical?

      Maybe you should READ the damn thing and notice how that's addressed in the first half-page.

      It's not completely addressed or at least all the implications are not spelled out. They talk about dealing with sparse matrices but they would have to be O(log n) sparse to be useful for a single application of the algorithm. For example, a matrix with n=1000000 would have to have around 15 non-zero values and a trillion zero values. I don't know if that's practical.

      It still might be useful if one needs to perform the operation repeatedly say for an iterative algorithm. As long as one only loaded the O(n) data once. However, I doubt that is likely for quantum computers since one probably needs to reset the quantum state. However, perhaps the algorithm can be adapted to solve iterative problems.

      --

      Chris Mesterharm
    4. Re:Seems bogus by adrianwn · · Score: 3, Informative

      They talk about dealing with sparse matrices but they would have to be O(log n) sparse to be useful for a single application of the algorithm. For example, a matrix with n=1000000 would have to have around 15 non-zero values and a trillion zero values.

      Wrong. An upper bound in big O notation does not give any indication as to constant factors of the "real" bound (nor to other summands which are in o(log n)). In fact, your statement doesn't even make sense, because it is an asymptotical bound and hence can't be applied to a fixed size of the input size.

    5. Re:Seems bogus by mesterha · · Score: 1

      Wrong. An upper bound in big O notation does not give any indication as to constant factors of the "real" bound (nor to other summands which are in o(log n)). In fact, your statement doesn't even make sense, because it is an asymptotical bound and hence can't be applied to a fixed size of the input size.

      It's an example, to give a feel for the order of magnitude. If the particular constant was very large, one would have to increase n to show the same effect, but the idea would hold. In addition, it has nothing to do with my argument. You can mentally delete that sentence if it bothers you. It has no impact on my point.

      --

      Chris Mesterharm
    6. Re:Seems bogus by buchner.johannes · · Score: 1

      In quantum computing, (O)(o) reads you!

      That doesn't make sense. But the smiley is nice.

      --
      NB: The message above might reflect my opinion right now, but not necessarily tomorrow or next year.
  4. Except... by Anonymous Coward · · Score: 0

    It can only solve the problems exponentially faster if no-one is looking.

    1. Re:Except... by Anonymous Coward · · Score: 0
      Ceiling cat is watchin'...

      ..ruinin' your xperiment.

  5. Re:Thoughts? by lancelotlink · · Score: 0, Offtopic

    The unfortunate darker side of online anonymity.

  6. Re:not able to be used == not useful by Andr+T. · · Score: 4, Insightful
    Maybe it's just a story, but I've read something about Faraday that made me think about what you've written.

    When the Prime Minister asked him about a new discovery, "What good is it?", Faraday replied, "What good is a newborn baby?"

    --

    Any life is made up of a single moment, the moment in which a man finds out, once and for all, who he is.

  7. Re:not able to be used == not useful by norton_I · · Score: 4, Insightful

    You think that quantum computers are not able to justify grants or PhDs? What world are you living in?

    until these quantum computers exist and are cheap enough to fill datacentres

    Yeah, because classical computers were never useful to anyone (or anyone important) until datacenters existed.

    No, to be really useful, quantum computing has to be as easy to afford and deploy as current computing technology.

    And until then, developments that bring us closer are irrelevant? Applications that could give us more reason to develop the technology are pointless?

    What exactly is your point here?

  8. Polynomial Speedup by Anonymous Coward · · Score: 0

    This is amazing research, and if it works it will be more powerful than the FFT, and maybe even quicksort.

    However, the article make a mistake in calling this an exponential improvement. Even the slowest solving algorithm (QR) is O(n^3). This promises O(log(n)). This is only a polynomial speedup.

    That being said, this still kicks ass, and I hope it works.

    1. Re:Polynomial Speedup by Anonymous Coward · · Score: 0

      No, exp(log(n^k)) = n^k, hence the term exponential speed up.

    2. Re:Polynomial Speedup by blueg3 · · Score: 4, Informative

      To rephrase the other response, log vs. polynomial is the same as polynomial vs. exponential. Moving from polynomial time to logarithmic time is an exponential speedup (just as is moving from exponential time to polynomial time is).

      O(n^3) vs. O(log n)
      ->
      O(exp(n^3)) vs. O(n)

    3. Re:Polynomial Speedup by steelfood · · Score: 1

      To clarify:
      O(n) vs. O(log n) -> O(2^n) vs. O(n)

      --
      "If a nation expects to be ignorant and free in a state of civilization, it expects what never was and never will be."
  9. Re:not able to be used == not useful by MoellerPlesset2 · · Score: 1

    It's not a 'new toy' for computer science. Computer science has pretty much nothing to do with it. Mostly, it's a toy, or rather, academic persuit for theoretical physicists.
    You will not be seeing Quantum Computers taking over general-purpose computing tasks anytime soon. Personally, I'm very skeptical to whether we will ever see such a thing happen. Because it will almost certainly never be easy and affordable to deploy; because I very much doubt you could ever get the necessary long decoherence times required for a quantum computer of any size to work, in an easily achievable environment. (by which I mean something approaching room temperatures, for instance).
    IOW, a computer that's a fancy elaboration on an NMR machine will never be a easy nor affordable.

  10. Re:not able to be used == not useful by bmwm3nut · · Score: 2, Insightful

    I see your point, but think conversely: I make a quantum computer that's cheap enough to fill a data center but there's no algorithms out there? What use is it? We need the physicists our there making the quantum computers and we need the computer scientists out there developing the algorithms. One without the other is useless. Also think of this: Dijkstra's "Go To Statement Considered Harmful" was published in the late 60's, there weren't many cheap computers to fill data centers then. He was working on the theory of algorithms not worrying about how to actually implement it. The same thing here, there are people working on the theory of these algorithms, other people will worry about actually using it when the time come.

  11. Re:not able to be used == not useful by Ambitwistor · · Score: 2, Insightful

    I know quantum is the 'new toy' in computer science, but seriously, until these quantum computers exist and are cheap enough to fill datacentres with, no-one outside of academia is going to get any useful work from them.

    Er, yes. If there aren't any quantum computers then quantum computers aren't useful. That's not the point of this work. The point of this work is primarily to present a new algorithm for which quantum computing shows exponential speedup, which is an interesting theoretical issue in computer science. If quantum computers ever become practical, then this algorithm will be too, but no one has claimed that this algorithm is useful today. (The submitter noted explicitly that it is not.)

  12. n to log(n) by rcallan · · Score: 3, Informative

    The summary cleverly omits that solving a linear equation is neither NP complete nor NP hard, the speed up is from O(n) to O(log n). I think you'd need a ginormous matrix for this to be useful depending on the constants and such (Of course it'd be crime for me to read paper instead of the abstract to actually find out the details). They already have the applications for quantum computing, it will be much more interesting when they actually figure out a way to build the damn things.

    I'm sure it's still a significant result and there's a good chance they did something new that can be used in other applications.

    1. Re:n to log(n) by popmaker · · Score: 2, Insightful

      Often, one does not need to know the solution x itself, but rather an approximation of the expectation value of some operator associated with x, e.g., xMx for some matrix M . In this case, when A is sparse and well-conditioned, with largest dimension n, the best classical algorithms can ïnd x and estimate xMx in O(n) time. Here, we exhibit a quantum algorithm for solving linear sets of equations that runs in O(log n) time, an exponential improvement over the best classical algorithm.

      This is a long quote, which is at top of the actual paper cited (I'd trim it down, but I'd need to brush op on my linear algebra to be sure not to ruin it).

      According to them, the best algorithms are O(n) and their algorithm improves that to O(log n). It has nothing to do with P vs NP but it is an exponential improvement anyway (going from n to log n), as promised in the summary.

    2. Re:n to log(n) by kvezach · · Score: 1

      If you're an evil socialist (or just a planner faced with limited resources), you can also use the exponential speedup to invert detailed Leontief matrices quickly. That's pretty useful. As for expansion, well, let's just hope there's a similar speedup to be found in linear programming :)

    3. Re:n to log(n) by hotdiggitydawg · · Score: 1

      A Slashdot summary that is still technically correct, despite the usual omission of key facts?

      I think your discovery is perhaps even more notable than the algorithm!

    4. Re:n to log(n) by Anonymous Coward · · Score: 0

      This _is_ important. You say that you'll need ginormous matrices for this to be useful... but ginormous matrices are _always_ wanting to be inverted. Pretty much all applied mathematics problems end up being reduced to a problem of linear algebra. An exponential speed-up on this problem would be a great advance for our civilization. Of course, we need real quantum computers for it to be at all useful.

    5. Re:n to log(n) by Darby · · Score: 1

      As for expansion, well, let's just hope there's a similar speedup to be found in linear programming :)

      Simplex method forever, Baby!

    6. Re:n to log(n) by Timmmm · · Score: 1

      > I think you'd need a ginormous matrix for this to be useful

      There are ginormous matrices. For example finite element analysis often uses matrices with millions of rows.

    7. Re:n to log(n) by Anonymous Coward · · Score: 0

      I think you'd need a ginormous matrix for this to be useful...
      A big matrix helps to take advantage of that yes, but in just about any scientific computing problem, the solver would like nothing more than too increase the size of the matrix by a lot. They don't b/c it imposes unreasonable time constraints. Hint: I work in scientific computing (okay not science per se, it's engineering but w/e)

    8. Re:n to log(n) by Anonymous Coward · · Score: 0

      I can think of hundreds(not joking) of examples where solving a linear system of large size is important. Ignoring the obvious ones for a moment, sparse matricies like the ones being viewed in this article are the basis for simulations of almost all types. A few examples: Quantum simulations(you know - the ones which could predict chemical qualities from a theoretically possible structure), fluid dynamic simulations(The ones we are spending billions of dollars to do to study climate change). Infact, theres a good chance that this can be applied to solveing linear programming problems - you know, the ones like, how should you arrange bus routes in your city, or run supply lines in a war, or how to invest your stokes optimally. None of these problems can be solved _well_ with current systems, because they're too large. Dropping them to logarithmic time would be one of the most important things to have happened _ever_. People talk about mores law - this beats it for advancement of the fundamentals of our society. This will have a bigger impact for us being able to advance computational problems. The fact that these aren't NP complete or NP hard is unfortunate - fine. But don't for a moment claim that this isn't a massive break through.

      My only regret here, is that this appears to largely apply to SPARSE matrices. These are common zero heavy matrices, but this algorithm isn't generally applicable.

    9. Re:n to log(n) by tcjohnson · · Score: 1

      Slow down there. Solving an NxN system of linear equations is a O(n^3) operation in the dense case. (Yes, you can speed it up with LU decomposition(if you want to solve the same matrix with lots of b matrices) for an O(n^3) once and O(n^2) after that, or might be able to get a better iterative scheme(though you can't really plan on it).) Your point still remains about not being NP-complete or NP-hard. But it's one more thing we could do with quantum computing, and I'd still be pretty satisfied with myself if I could take an O(n^3) to O(log n).

    10. Re:n to log(n) by bloobloo · · Score: 1

      Analysis of pollution monitoring stations, using historical wind flow analysis to determine where in the world pollution has been released from.

      ABSOLUTELY ginormous matrices are used for this.

  13. Political Consequences thereof... by KudyardRipling · · Score: 1

    Has anyone spoken on its applications vis-a-vis cryptography and cryptanalysis?

    --
    Submission as evidence constitutes plaintiff and/or prosecutorial misconduct.
    1. Re:Political Consequences thereof... by professorguy · · Score: 1

      I don't think any current crypto uses the solution of simultaneous equations as its trapdoor function. So this has no direct effect on the current state of affairs. Does it open up the possibility of a new trapdoor? I don't think so, but I wasn't clever enough to come up with this algorithm either.

  14. Could this break RSA/public key crypto? by gillbates · · Score: 0

    I can't help but wonder how (if?) this is going to affect public key cryptography. RSA security is dependent on the difficulty of factoring large primes, and this seems like it would reduce the time required to solve the problem considerably.

    Perhaps someone more versed in mathematics can shed some light on this.

    --
    The society for a thought-free internet welcomes you.
    1. Re:Could this break RSA/public key crypto? by Andr+T. · · Score: 1

      This has been covered in another article

      --

      Any life is made up of a single moment, the moment in which a man finds out, once and for all, who he is.

    2. Re:Could this break RSA/public key crypto? by kmac06 · · Score: 1

      Shor's algorithm (explicitly mentioned in the summary) is an old quantum algorithm to factor primes.

    3. Re:Could this break RSA/public key crypto? by Darby · · Score: 1

      RSA security is dependent on the difficulty of factoring large primes, and this seems like it would reduce the time required to solve the problem considerably.

      Factoring primes is the easiest freaking thing in the world.
      Give me a prime, any prime. Ok, its factors are it and 1.

      Perhaps someone more versed in mathematics can shed some light on this.

      HTH HAND.

  15. Re:not able to be used == not useful by Anonymous Coward · · Score: 0

    And when/if the quantum computers become ready, you want to have to wait 20 years for the basic research necessary to make them usable? All research like this is useful, even if it leads nowhere right now.

    I'm reminded of a nice little story I was told in my first year number theory course:

    There was a mathematician who was extremely proud that his particular branch of mathematics was so obscure that it had absolutely no practical use and was purely theoretical. This branch formed the basis of modern encryption that is used constantly in everyday life now.

    Anyone know the name of this mathematician, or am I completely getting this story wrong?

  16. Practical Application?! by 31415926535897 · · Score: 1

    All other algorithms either solve problems with no known practical applications

    Yes, because all quantum algorithms are hugely practical these days...

    1. Re:Practical Application?! by blueg3 · · Score: 1

      You have your word semantics wrong. Shor's algorithm has enormous practical application. However, as there are no computers to run it, it's impractical to actually put it to use.

  17. Re:not able to be used == not useful by Ambitwistor · · Score: 4, Interesting

    It's not a 'new toy' for computer science. Computer science has pretty much nothing to do with it. Mostly, it's a toy, or rather, academic persuit for theoretical physicists.

    No, it's of real interest to theoretical computer science. Quantum computing defines a new class of algorithmic complexity: there are, for instance, sub-exponential quantum algorithms for problems which have only exponential-time classical solutions. There is a whole subindustry of algorithmic complexity theory devoted to exploring the differences between algorithms that can be executed on quantum computers and those which are executed on classical computers. Scott Aaronson's lecture notes are a good introduction to this subject.

  18. Re:Thoughts? by Anonymous Coward · · Score: 0

    Survival of the fittest... these jigaboos know it, and KNOW that they are inferior to us, and will die out eventually

    lol, have you ever seen a child of a black and white couple? Is it white? No. Is it black? No.
    If anything the entire human race will become less white and less black. Maybe some day we will all be blue and these stupid racial issues will finally be behind us. Maybe then, the human race as a whole, has left its stage of infancy.

  19. Re:not able to be used == not useful by physicsphairy · · Score: 2, Insightful

    I could just as well argue that there is nothing useful about developing quantum computers until we have programs we can run on them.

    This is not tangential science. The is the real groundwork for the development of the new technology. Without this sort of work quantum computers will simply never exist.

    So pointing out its lack of present utility is like pointing out that after laying the foundation for a house that you still have nothing to live in. That may be true, but in so far as the initial step is pre-requisite to your ultimate goal, it is erroneous to dismiss it as 'not useful.'

  20. Re:not able to be used == not useful by thermian · · Score: 1, Troll

    Maybe it's just a story, but I've read something about Faraday that made me think about what you've written.

    When the Prime Minister asked him about a new discovery, "What good is it?", Faraday replied,
    "What good is a newborn baby?"

    Wrong, actually it was in reference to his new electric motor, and the proper quote is 'When asked by the kind what use it was, Faraday replied, 'One day sir, you may tax it'.

    Note also at that point the electric motor existed, quantum computers do not, not in any useful sense.

    --
    A learning experience is one of those things that say, 'You know that thing you just did? Don't do that.' - D. Adams
  21. arXiv articles - question by blind+biker · · Score: 2, Informative

    Are arXiv articles peer-reviewed?

    If not (as I suspect), that puts a serious question mark on them. On the other hadn, there are excellent non-peer reviewed scientific articles - and almost all the scientific articles produced in Europe before the 2nd WW were not peer-reviewed (back then that was an american practice, and a very good one I would add). However, nowadays peer review is a valuable and available resource that should be utilized.

    THAT SAID again... some of the best, most innovative scientific articles are not being, nowadays, accepted for publication because the reviewers are one degree too dumb for the article. Eventually they do get published, but with an unnecessary 5-6 year delay.

    Also, I have read in my life thousands of published peer-reviewed articles, and many of them contain incredible imbecillities where I have to question whether all the reviewers were high on hallucinogens. Very very high on hallucinogens.

    --
    "The agriculture ministry is not in charge of Gundam" - Japanese ministry official.
    1. Re:arXiv articles - question by MozeeToby · · Score: 1

      I thought it had been nearly proven that peer review for highly specialized complez subjects was pretty much worthless, since most reviewers will not understand the subject matter and also won't be willing to admit that they don't understand it. Didn't some students at MIT create a giberish generating program that was able to produce papers that pass peer review?

      The basic problem is, for truly ground breaking research, there often isn't a ready supply of peers to do the review. There are plenty of subjects in science where litterally a dozen or less people in the world qualified to do the review. And in all likelyhood, 4 of them collaborated on the research in question and another 6 were consulted at some point during the research.

    2. Re:arXiv articles - question by fph+il+quozientatore · · Score: 4, Funny

      Are arXiv articles peer-reviewed?

      No, they aren't.

      --
      My first program:

      Hell Segmentation fault

    3. Re:arXiv articles - question by Chocky2 · · Score: 1

      arXiv holds preprints, so no -- they've not been peer-reviewed.

      However it has moderation and endorsement systems which (in theory) spot any Archimedes Plutonium wannabes.

    4. Re:arXiv articles - question by Anonymous Coward · · Score: 0

      Wow, you've read thousands of published peer-review articles, but you don't know whether or not arxiv articles are peer-reviewed?

      Colour me skeptical.

    5. Re:arXiv articles - question by Chocky2 · · Score: 1

      Didn't some students at MIT create a giberish generating program that was able to produce papers that pass peer review?

      I doubt it, unless they were sociologists :)

      Peer review may not be able to reliably tell for certain if something is correct, but it's often a good mechanism for spotting things that are wrong.

      You don't need ten years post-doc work in QCD to spot an error in addition, though if you're trying to extend the number of colours in a gauge theory you probably do :)

    6. Re:arXiv articles - question by Saysys · · Score: 1

      I thought it had been nearly proven that peer review for highly specialized complex subjects was pretty much worthless, since most reviewers will not understand the subject matter and also won't be willing to admit that they don't understand it.

      No. Speaking as a scientist involved in esoteric areas: That program was a farce, it was accepted for "review" at a scientific conference, a much lower standard. When it comes to a conference someone who is simply interested in the title might allow the paper in.

      As for important research: If you are publishing in a good journal, something that has more citations than articles published, then you will have someone who knows enough about the subject to give it a reasonable review.

    7. Re:arXiv articles - question by Anonymous Coward · · Score: 0

      heh...most of those were not a paper attempting to prove the riemann hypothesis, and those that were had tons of reviews pointing out mistakes. At least one was withdrawn by the author once the mistake was pointed out.

      Sounds like a more thorough peer-review than most other journals. I think arxiv is the future.

    8. Re:arXiv articles - question by blind+biker · · Score: 1

      Didn't some students at MIT create a giberish generating program that was able to produce papers that pass peer review?

      I don't know. But sure as heck would like to - any more info on this so I can look it up?

      --
      "The agriculture ministry is not in charge of Gundam" - Japanese ministry official.
    9. Re:arXiv articles - question by blind+biker · · Score: 1

      Wow, you've read thousands of published peer-review articles, but you don't know whether or not arxiv articles are peer-reviewed?

      Colour me skeptical.

      I have never read a single arXiv article. I've seen a few titles and abstracts, though.

      --
      "The agriculture ministry is not in charge of Gundam" - Japanese ministry official.
    10. Re:arXiv articles - question by XchristX · · Score: 1

      Peer-review isn't always what it's cracked up to be. Read about the Bogdanov controversy that erupted in my uni some years back that exposes some serious flaws in the peer-review process.

      http://en.wikipedia.org/wiki/Bogdanov_Affair

      --
      l'Homme n'est Rien l'Oeuvre Tout: Gustave Flaubert to George Sand
    11. Re:arXiv articles - question by LeadSongDog · · Score: 1

      Try clicking on that thingamabob that says "PDF".

      --
      Oh, I'm sorry sir, I thought you were referring to me, Mr. Wensleydale.
    12. Re:arXiv articles - question by Helios1182 · · Score: 2, Interesting

      Yes and no. It was a program called SciGen. The purpose was to weed out conferences that are crap. The ones that exist to take, and make money, rather than really promote scholarly work.

      ---

      About:

      SCIgen is a program that generates random Computer Science research papers, including graphs, figures, and citations. It uses a hand-written context-free grammar to form all elements of the papers. Our aim here is to maximize amusement, rather than coherence.

      One useful purpose for such a program is to auto-generate submissions to conferences that you suspect might have very low submission standards. A prime example, which you may recognize from spam in your inbox, is SCI/IIIS and its dozens of co-located conferences (check out the very broad conference description on the WMSCI 2005 website). There's also a list of known bogus conferences. Using SCIgen to generate submissions for conferences like this gives us pleasure to no end. In fact, one of our papers was accepted to SCI 2005! See Examples for more details.

      http://pdos.csail.mit.edu/scigen/

    13. Re:arXiv articles - question by 1729 · · Score: 1

      Peer-review isn't always what it's cracked up to be. Read about the Bogdanov controversy that erupted in my uni some years back that exposes some serious flaws in the peer-review process.

      http://en.wikipedia.org/wiki/Bogdanov_Affair

      Or read about the ongoing El Naschie affair:

      http://golem.ph.utexas.edu/category/2008/11/the_case_of_m_s_el_naschie.html

    14. Re:arXiv articles - question by tehgnome · · Score: 1

      Before I begin, let me mention that I am speaking about the mathematical world(one of the fields in which this paper was written). The following comments may not apply to other fields as I have no expertise. First of all, as the other reply mentions, no in fact they are not peer reviewed. That being said, arXiv is a preprint server and thus the content is fairly respectable. Additionally, this paper is by two authors at MIT the third at Bristol (fairly respectable schools).

      Second, in the modern mathematical community, an enormous amount of important papers are not published. This is not a result of dumb reviewers, in fact most journals have a system for preventing this sort of issue. Their system is simple, most papers are reviewed by two people, each an expert in the field. I cannot argue that sometimes the paper will be beyond the scope of the reviewer, but with the connectedness of the mathematical community at present day, it is highly unlikely. The reason many papers go unpublished now, is because of arXiv and other preprint servers. Older faculty members have no need to boost their publication count so the actual publication is unnecessary. Additionally, most papers are only readable by a small subset of the mathematical community, and they are contacted directly. Also, nearly all mathematicians at this point are familiar with arXiv and use it as their main source of current research, thus reducing the need of publication. Third,

      Also, I have read in my life thousands of published peer-reviewed articles

      I am calling bullshit on this. I am currently in graduate school at a major university. There are several world famous professors here and one in particular is known for his ability to sift through papers extremely quickly. He doesn't read them, just skims to get the basic idea. He only gets through a paper a week maybe two. Assuming you are more consistent than him, and read two per week. And being more generous you blaze through 100 a year. You would be working at this pace for 20 years. While not impossible, highly unlikely. Especially since you mentioned that you "read" them not skim, and furthermore you are able to check them for trivialities, which takes considerable more time considering that you would have to evaluate the status of the paper.

      --
      She must be a TIGER in the bathroom... I mean bedroom... ~Ryan
    15. Re:arXiv articles - question by blind+biker · · Score: 1

      I read about the WMSCI 2005 fiasco. That's not really a merit of the paper generated by SCIgen, I think, but the fact that WMSCI 2005 did not actually review the submitted papers. Correct me if I'm wrong. In any case, WMSCI 2005 comes out as total losertown.

      I briefly read through the WMSCI 2009 call-for-papers, and they now seem to have a double-boind review, and something strange: "a non-blind, open reviewing by means of 1-3 reviewers suggested by the submitting authors." I can see potential for abuse in the latter.

      Oh well. I wouldn't consider WMSCI an appropriate place at this point in my career anyway.

      --
      "The agriculture ministry is not in charge of Gundam" - Japanese ministry official.
    16. Re:arXiv articles - question by Anonymous Coward · · Score: 0

      It obviously depends on the reviewers and the journal. I remember seeing that story on the MIT papers, but it's not relevant here.

      there are other MIT researchers that have been at the ground floor of quantum computation, and some of them got tenure out of it. So, not everything is inscrutable or trivial.

    17. Re:arXiv articles - question by blind+biker · · Score: 1

      I am calling bullshit on this. I am calling bullshit on this. I am currently in graduate school at a major university. There are several world famous professors here and one in particular is known for his ability to sift through papers extremely quickly. He doesn't read them, just skims to get the basic idea. He only gets through a paper a week maybe two. Assuming you are more consistent than him, and read two per week. And being more generous you blaze through 100 a year. You would be working at this pace for 20 years. While not impossible, highly unlikely. Especially since you mentioned that you "read" them not skim, and furthermore you are able to check them for trivialities, which takes considerable more time considering that you would have to evaluate the status of the paper.

      And if I was thoughtless and narrow-minded like you, I'd call bullshit on what you just wrote there, because my experience is completely different. I read (not just skim through) one to two papers a day on a normal day, and more when I'm writing. I read more than a hundred papers when I wrote my review. I read (and work in) the field of nanotechnology, materials science, (integrated and semiconductor) chemical and other sensors, and chemistry in general is extremely important for my research. The reason I don't call bullshit on what you wrote, even though I did read thousands of papers (not just skimmed through) is because I can imagine that mathematics papers require more time to understand, than for example materials science.

      I would suggest for your experience as a human person, to talk with colleagues in your graduate school's institution that are in other fields than your own, and see what their experience as well as paper-reading "performance" can be. If you do, I am guessing that you will be somewhat amazed. I am assuming that you did not, in fact, bullshit me about

      There are several world famous professors here and one in particular is known for his ability to sift through papers extremely quickly. He doesn't read them, just skims to get the basic idea. He only gets through a paper a week maybe two.

      which I find almost incredible, but being that you're in math, I will take your word for it.

      For the record, my advisor (actually, I prefer to call him boss) is more focused and can read more papers than me, per unit time. I have a mild problem of ADD that hampers my efforts sometimes. It's related to my Aspergers syndrome.

      --
      "The agriculture ministry is not in charge of Gundam" - Japanese ministry official.
    18. Re:arXiv articles - question by tehgnome · · Score: 1

      I apologize, I was acting pretty narrow-minded. In my first draft of my post I didn't even include the disclaimer first paragraph, but then i realized the possibility that other fields have more homogeneous techniques. I applaud you and am jealous that you are able to sift through that volume of material, even only reading 6 papers currently for my Ph.D., I find the amount of material enormous and ridiculously daunting.

      --
      She must be a TIGER in the bathroom... I mean bedroom... ~Ryan
    19. Re:arXiv articles - question by Anonymous Coward · · Score: 0

      Are arXiv articles peer-reviewed?

      No.

    20. Re:arXiv articles - question by blind+biker · · Score: 1

      Apology very much accepted. This behaviour shows honesty and a lack of ego (both important in science... and life).

      Now.. are you telling me your PHD work will only have 6 references? That's, again, almost incredible to me. A colleague of mine and I have come up with a rough number of references per PHD: it's about the number of pages, including appendices. In your field, it seems it's about the tenth or less than that. Which explains the one-paper-per-week or less. I love maths, but I am glad I'm where I am and let you be where you are :o)

      First thing on Monday I'll try to get in touch with some math people I know and ask them about this whole issue. Seems like I would never be able to get through an average contemporary maths paper, which is quite disconcerting as I always thought I'm a polyvalent scientist and person.

      --
      "The agriculture ministry is not in charge of Gundam" - Japanese ministry official.
    21. Re:arXiv articles - question by Anonymous Coward · · Score: 0

      It's not peer reviewed, but it's typical to post pre-prints of articles on arXiv before they get published in a peer-reviewed journal they've been submitted to (some journals don't allow this). Also, Seth Lloyd's group is well known and respected, so it's not a paper from some crackpot.

    22. Re:arXiv articles - question by tehgnome · · Score: 1

      please don't misconstrue my explaination. Most phds have somewhere between 20-50 references and pages is the least important criteria. The six I speak of are what my work is based off of. Many other papers give important definitions examples or inspirations, but I won't read these, nearly extract the tidbit I need. Furthermore, I am currently in the first step of the PhD which is background literature review. I am taking a detailed survey of work done previously on quantized Schubert cell(my research area). Additionally many papers will be cited for their influence on the field and papers I am using, to provide a bed of expected knowledge for those wishing to read the PhD.

      --
      She must be a TIGER in the bathroom... I mean bedroom... ~Ryan
    23. Re:arXiv articles - question by Anonymous Coward · · Score: 0

      Are arXiv articles peer-reviewed?

      No, but the vast majority of them are either finished with peer review or in the process of peer review for a published journal. Articles on ArXiv are by-and-large comparable in quality to peer reviewed articles, and this is probably because researchers still need to pass peer review elsewhere.

      Eventually they do get published, but with an unnecessary 5-6 year delay.

      It isn't that bad. Usually.

      Also, I have read in my life thousands of published peer-reviewed articles, and many of them contain incredible imbecillities where I have to question whether all the reviewers were high on hallucinogens.

      I really think you ought to be more careful about criticizing others' work. It's very difficult to evaluate a scientific paper if you aren't qualified to act as a reviewer. To be honest, I doubt you're qualified to evaluate thousands of papers at that level. I'm not trying to be rude, but I do wish people would think twice before saying things like that.

    24. Re:arXiv articles - question by Anonymous Coward · · Score: 0

      Arxiv.org is not peer reviewed but you're missing the point. Arxiv.org is a website that people post their papers before they get published. Of course some of them might be gibberish and will never be published but every scientist that respects himself and his work, will put his paper on arxiv.org so that it is available to everyone. As you may know, getting the journal itself is extremely expensive (unless your university has a subscription) so the website is an excellent way to share your work. Now this is an important finding in the area of quantum computing, so if it is correct (which it looks like it is but I'm not a reviewer) it will be published. If it wasn't on arxiv.org you probably wouldn't have been able to read it.

    25. Re:arXiv articles - question by omuls+are+tasty · · Score: 1

      So?

  22. Re:not able to be used == not useful by Andr+T. · · Score: 3, Informative

    I think he liked to say things like those, because I just found a page quoting him just like I said.

    --

    Any life is made up of a single moment, the moment in which a man finds out, once and for all, who he is.

  23. Looks like a big deal to me. by jonniesmokes · · Score: 4, Informative

    Finally a cool article on /. This is extremely cool! There are a lot of problems in the real world that have extremely large sparse matrices that need to be inverted. Fluid dynamics and solutions to Maxwells equations come to mind. But I am sure there are other applications in relativity and plasma physics. Estimating a solution to a linear dynamic system of say 2^128 degrees of freedom in only 128 cycles would change a lot of things.

    And... Yes, we are working very hard on building the computers.

  24. Re:not able to be used == not useful by thermian · · Score: 1

    You think that quantum computers are not able to justify grants or PhDs? What world are you living in?

    One where I read peoples comments properly before replying to them. I did not say that at all.

    Yeah, because classical computers were never useful to anyone (or anyone important) until datacenters existed.

    We use datacentres *now* we didn't use them before. These days people in the real, working world need access to computing power in ways that we didn't before. I am talking practicality. The kinds of applications that get companies investors.

    And until then, developments that bring us closer are irrelevant? Applications that could give us more reason to develop the technology are pointless?

    What exactly is your point here?

    Irrelevant is not the same as useless. It is, 'a lack of relevance', look it up. Academia will continue to explore the issue, but until we see deployments of quantum computers in large enough numbers to start basing the computer 'economy' on them they lack real world relevance.

    --
    A learning experience is one of those things that say, 'You know that thing you just did? Don't do that.' - D. Adams
  25. Quantum Computing needs a language by linzeal · · Score: 1

    Do you realize, that until they begin solving these problems in academia that there will be no industry-ready solution? I mean this is a whole new advent of computing really with three-dimensional processors coming online at around the same time we may see the same sort of increase in computational power that they did with the first electric computers.

    This are some workable challenges that lay ahead in the next few years.

    1. Not only will a lot of algorithm design need to be hacked out but I think Quantum Computing needs its own language to really shine and that can be worked on now.

    2. A lot of work can be made possible with a clever and cheap single or dual qubit hardware solution that is yet to be designed. Please make the connection USB. The boys and girls down in applied physics may be able to help you. Like Morlocks they usually are underground and desire a eloi/hippy for snackerfice.

    3. The ability to run an exponentially greater amount of calculations is going to lead to revolutionary engineering breakthroughs across the board. Lattice work in concrete is particularly linear, curvilinear or hodge-podge; now imagine lattice inside a concrete pylon like a fractal tree, it could be made to withstand force vectors that would turn a standard pylon to dust, sure we have the computing power to do a pylon like that now but not all the components of a 1000 story building.

    1. Re:Quantum Computing needs a language by cnettel · · Score: 1

      2. There is no problem in doing single or dual qubits in hardware for desktops. You can simulate all of it far cheaper. After all, that's how we test the algorithms right now, and we could easily handle even 20 or so qubits within realistic time.

  26. Avinatan Hassidim and Seth Lloyd by aram.harrow · · Score: 5, Informative
    are my coauthors, and the ordering of author names was alphabetical, and doesn't reflect our level of contributions (which were more or less equal).

    So please cite this as "Harrow, Hassidim and Lloyd" and not "Harrow and coauthors."

    That said, we're pleased about that attention. :)

    In response to one question: the matrix inversion problem for the parameters we consider is (almost certainly) not NP-complete, but instead is BQP-complete, meaning that it is as difficult as any other problem that quantum computers can solve. We plan to update our arXiv paper shortly with an explanation of this point.

    1. Re:Avinatan Hassidim and Seth Lloyd by saburai · · Score: 2, Insightful

      I work in CFD, so this is all thrilling to me. I suspected it was only a matter of time before methods were discovered for applying quantum computation to large systems of linear equations, and I certainly hope your work stands up to peer review. Cheers!

      --
      All stated opinions are subject to further review
    2. Re:Avinatan Hassidim and Seth Lloyd by wolfemi1 · · Score: 2
      Aram,

      It's Mike Wolfe, congratulations on making Slashdot, if this is your first time. What a happy surprise seeing your name there!

      -Mike

    3. Re:Avinatan Hassidim and Seth Lloyd by JohnFluxx · · Score: 1

      It's awesome that you posted here :)

      A quick question if I may..

      Could raytracing be done efficently on quantum computers?

    4. Re:Avinatan Hassidim and Seth Lloyd by LeadSongDog · · Score: 1

      So what we really want to know is, will this work for weather forecasts. One wants to put the butterfly in the right place, after all.

      --
      Oh, I'm sorry sir, I thought you were referring to me, Mr. Wensleydale.
    5. Re:Avinatan Hassidim and Seth Lloyd by joe_frisch · · Score: 1

      As the size of the linear equation problem increases, does the quantum state become more "fragile" (I'm sorry, I don't know the correct terminology). Would a hypothetical quantum computer need to operate at lower temperature, and does this create a limit on the size of problems that could be solved with this technique?

    6. Re:Avinatan Hassidim and Seth Lloyd by khallow · · Score: 1

      Does this solution help with the more general case of finding the solution to a dense, well conditioned system of linear equations? I briefly glanced over the Andrew Childs paper you cited, but enlightenment did not sink in.

    7. Re:Avinatan Hassidim and Seth Lloyd by MoxFulder · · Score: 1

      Great work, Aram! I can't believe you managed to get your name on slashdot. I seethe with jealousy.

      Heck, I'd settle for having a decent paper to put on arXiv!

      -Dan Lenski

    8. Re:Avinatan Hassidim and Seth Lloyd by aram.harrow · · Score: 1
      The dense case is an interesting open question. We'd really like to know more about that.

      I don't know much about ray-tracing, but I thought it used 3x3 and 4x4 matrices, so for that our speedup wouldn't be particularly useful. More generally, measurement in quantum computers is likely to be painful, so we think the most dramatic quantum speedups will occur when the answer is a few bits, rather than megabytes, as occurs in ray tracing.

      Chaotic systems we also probably can't do much with yet, but my friend Tobias Osborne is working on something that may be applicable.

      As for fragility, this is addressed through fault-tolerant quantum computing techniques, just like for any other quantum algorithm. It's not easy, but it's in principle possible.

      Dan and Mike: Hi! :)

    9. Re:Avinatan Hassidim and Seth Lloyd by bloobloo · · Score: 1

      I see a new sci-fi channel B-movie in your post...

  27. Re:not able to be used == not useful by Anonymous Coward · · Score: 0

    I think you're just grumpy that you're wrong. Wrong about each of the responses that you've made to people replying to yours. Stop while you're at least a little ahead.
     
    Practical use, eh...I guess prime numbers aren't all too practical, with their many uses in crypto. Just a single example from the summary - maybe you should read the summary properly before replying to it.

  28. Re:not able to be used == not useful by DeadDecoy · · Score: 1

    I for one cannot wait until all the appropriate reading materials come out: Knuth's Fundamental Quantum Algorithms, Quantum Algorithms for Dummies, and Quantum Algorithms in a nutshell. :)

  29. Re:not able to be used == not useful by Anonymous Coward · · Score: 0

    It seems you didn't think quite through.

    Quantum computing would be a waste of time if you couldn't do anything with it.
    And as the article stated, before this algorithm, there wasn't much practical things that could be done, it's possible the practical use is very limited.

    You are saying people should focus on developing the hardware first because those algorithms are useless now. After developing the hardware, how dumb would you feel if you discovered there is not much practical use for that?

  30. Re:not able to be used == not useful by MoellerPlesset2 · · Score: 1

    No, it's of real interest to theoretical computer science. Quantum computing defines a new class of algorithmic complexity: there are, for instance, sub-exponential quantum algorithms for problems which have only exponential-time classical solutions.

    That implies putting the results of a physical measurement on equal footing with 'classical' methods, i.e. what can be done using pure math. If you do that, I think you're turning Computer Science from having been a branch of Mathematics into some completely different animal.

    Algorithms are math. They can be proven mathematically, etc. These 'quantum algorithms' are something different - even if they're derived mathematially (which is how physics works nowadays), they're essentially a statement of: Put this physical system in a certain state letting certain properties of the system represent your input. Manipulate it a certain way, and the 'algorithm' shows us that you can achieve a resulting state which - probabilistically - provides a measurable value representing the result of the 'calculation' you wanted to perform. It is not mathematically proven or provable (beyond the proof that the most probable state is the desired result).

    Which makes the methods essentially heuristics, not algorithms. And while that's perfectly good and useful for doing calculations and getting results, it is not a new kind of math, or any kind of math.

  31. Bzzzt, wrong! by fph+il+quozientatore · · Score: 1, Informative
    I can spot the first error in the abstract:

    In this case, when A is sparse and well-conditioned, with largest dimension n, the best classical algorithms can find x and estimate x^\dag M x in O(n) time

    First of all, "with largest dimension n" means nothing because if we are solving a linear system, we need A to be square. Then, the complexity of the best classical algorithms does not depend only on the size "n" of the matrix but also on the number "nnz" of non-zero entries.

    --
    My first program:

    Hell Segmentation fault

    1. Re:Bzzzt, wrong! by pablomme · · Score: 3, Interesting

      if we are solving a linear system, we need A to be square

      No. You can "solve" an under-determined system (i.e., reduce it). You can also "solve" an over-determined system via a least-squares fit. Both are common problems in scientific computing.

      --
      The state you are in while your HEAD is detached... - wait, what?
    2. Re:Bzzzt, wrong! by Anonymous Coward · · Score: 0

      No. You can "solve" an under-determined system (i.e., reduce it). You can also "solve" an over-determined system via a least-squares fit. Both are common problems in scientific computing.

      yes, but you only get a "solution" then

  32. Re:not able to be used == not useful by shoor · · Score: 1

    I read an autobiography of Benjamin Franklin which said that when Franklin was in France either negotiating the Treaty of Paris (that's the one where England actually recognized the USA as a separate country, ending the Revolutionary War), or maybe he was still just getting the French to back us, he was observing one of the first balloon flights of the Montgolfier bros, and someone wondered aloud what good was it, and his reply was "What good is a newborn baby?"

    BTW, I don't have "heroes", but if I did, Franklin would be my nr 1.

    --
    In theory, theory and practice are the same; in practice they're different. (Yogi Berra & A. Einstein)
  33. Re:not able to be used == not useful by Mr.+McGibby · · Score: 1

    So you're basically saying that probabilistic computation isn't math? That doesn't make any sense. Just because we have computers that are extremely reliable doesn't mean that probabilistic methods are unimportant. Quantum computers are showing us that they are.

    Richard Feynman would disagree. Please read his work on the Manhattan project.

    --
    Mad Software: Rantings on Developing So
  34. Re:not able to be used == not useful by nog_lorp · · Score: 2, Insightful

    Eh, in that case your post is irrelevant. It amounts to saying "Until we have x, people won't be able to use x, so it will only be of interest to people studying creating x". It goes without saying, and people on Slashdot are clearly interested in this.

  35. Re:not able to be used == not useful by Steneub · · Score: 2, Funny

    That depends. What is its tensile strength?

  36. Re:not able to be used == not useful by FrangoAssado · · Score: 3, Informative

    If you think quantum computing is about putting a physical system in a certain state and manipulating it, then you should also think classical computing is about setting a tape in a certain way and manipulating it.

    When Turing first described a computer (a turing machine), it was essentially a mechanism where you put a tape in a certain state, manipulate it according to certain rules and in the end you get the tape in another state containing the "result" of your computation. What was so interesting about it it that it was theoretically possible to build a machine that would be able to do the manipulations automatically.

    Quantum computation is analogous: get a certain vector in an n-dimensional Hilbert space, multiply it by these certain matrices in this specific order, and in the end you get a vector that corresponds to the "calculation" you did. This is absolutely only math, it has nothing to do with physics. What's exciting about this is that we expect to be able to build (real) machines that perform these operations way faster than any computer today can, because the specific operations with which be built our algorithm are exactly the things nature is capable of doing fast.

    Of course, we only discovered this when we discovered quantum mechanics -- that's the relation to physics.

  37. Re:not able to be used == not useful by Chris+Burke · · Score: 1

    Did you know that the foundations of computer science were laid down before the existence of the first electrical computer?

    Did you know that, when electrical computers came into existence, having this science all laid out already was actually pretty useful? Kept people from standing around going "Okay now what do we do?" for several years.

    In short, your view of utility is short-sighted and lacks vision.

    --

    The enemies of Democracy are
  38. Re:Thoughts? by MikeDirnt69 · · Score: 1

    Can we have a Quantum Linear Racist Resolver? This guy need help!

    --
    Am I eval()? - http://www.monst3r.com.br
  39. Re:not able to be used == not useful by canajin56 · · Score: 1

    First, go read the paper and then say that it doesn't contain "any kind of math."

    Second, explain how shooting electrons through doped silicon crystal gates, and then measuring the voltage across the end terminals isn't a physical measurement being put on equal footing with "pure math." I think that it is, so deterministic algorithms aren't algorithms either by your definition.

    Third, you're wrong. Lets take a 65536 bit long encryption key, the product of two very large primes. Lets factor them! The best known deterministic algorithm is going to take longer than the universe will last. But I bet it takes well under a second to check an answer for correctness! Let's say you have a quantum "algorithm" Q. You are correct, you can't prove Q(key) will produce the correct factorization. But you can CHECK it in only a second. So, run Q(key) until your check passes. There, that's an algorithm by your definition. You just used math to prove that if you run your quantum + classical hybrid computer on that input, it will always output the correct result.

    Fourth, an algorithm isn't a mathematical statement, stop redefining words just so you can get all riled up with righteous indignation. An algorithm is near universally defined as "a finite sequence of computational instructions, usually towards the end of computing a certain value or accomplishing a certain task." It's useless if you can't mathematically prove something about the answer. Deterministic algorithms you can always prove the answer is right (hopefully?). With randomized algorithms, you can mathematically prove that the answer is right too (in most cases) but not how long it takes. Conversely, you can usually also prove that it takes a finite amount of time, but then you can only prove a bound on it's probability of success, rather than being 100%. You're saying that it's "pure math" to prove (using math) that a sequence of instructions computes a correct answer in 1 year deterministically, but it's not pure math to prove (using math) that a sequence of instructions computes a correct answer in 1 year with probability of 1 - 1e-900. I submit that while the two are different proofs, for all intents and purposes, the two algorithms are equivalent, since you cannot have a computer that runs with 0 probability of errors, deterministic or not.

    --
    ASCII stupid question, get a stupid ANSI
  40. Re:Thoughts? by Anonymous Coward · · Score: 0

    If anything the entire human race will become less white and less black.

    Not really, everybody hates the mongrel bastards.

  41. Humor via moderation... by Hurricane78 · · Score: 0, Redundant

    ...FOR THE WIN! :D

    No, I will not explain this! :P

    --
    Any sufficiently advanced intelligence is indistinguishable from stupidity.
  42. A quantum linear equation by Hognoxious · · Score: 1

    I don't have a clue what a quantum linear equation is or why I'd need to solve it, let alone know how to.

    --
    Confucius say, "Find worm in apple - bad. Find half a worm - worse."
  43. Progress Bar? by Fujisawa+Sensei · · Score: 1

    What kind of side effects will a progress bar have since you can't know what its doing if you know where it is?

    --
    If someone is passing you on the right, you are an asshole for driving in the wrong lane.
  44. Re:not able to be used == not useful by MaskedSlacker · · Score: 2, Insightful

    He's my number 1 for being a genius AND a manwhore.

  45. Quantum of Solvethis by Anonymous Coward · · Score: 0

    Quantum of Solvethis.

  46. Other algorithms by Teppy · · Score: 1

    A cool algorithm that should be possible on a quantum computer is "perfect" data compression. IOW, "what is the smallest turing machine + input string that outputs the following string in less than 1 billion steps?"

    Such an algorithm would need a quantum computer to run, but the decompression could happen on a classical computer.

    Anyone aware if such an algorithm exists? The summary would seem to indicate not.

    1. Re:Other algorithms by Anonymous Coward · · Score: 0

      NP is not the same as BQP, as far as we know.
      So I am going to guess, no.

  47. Comparing Apples to Apples by internic · · Score: 3, Interesting

    This looks like a really interesting result, but having look a little at the paper it's not 100% clear to me what the quantum algorithm is being compared to. First a caveat, I study quantum physics but not CS, so my knowledge of algorithms and complexity theory is quite limited. Anyway, in solving problems on a good old classical computer, you can seek to solve a linear system exactly (up to the bounds of finite arithmetic) or you can seek to solve it approximately to within some error.

    So the thing I'm wondering is what classical algorithm are they comparing their result to, and is this comparing apples to apples? They say

    In this case, when A is sparse and well-conditioned, with largest dimension n, the best classical algorithms can find x and estimate x* M x in O(n) time. Here, we exhibit a quantum algorithm for solving linear sets of equations that runs in O(log n) time, an exponential improvement over the best classical algorithm. ... In particular, we can approximately construct |x> = A^-1 |b> and make a measurement M whose expectation value x* M x corresponds to the feature of x that we wish to evaluate.

    So it looks like the authors' algorithm gives an approximate solution to the linear system and they're comparing it to a classical algorithm that gives an exact solution to the problem. This seems like comparing apples to oranges. Perhaps someone who knows more about the features of the various classical algorithms can comment on whether it looks like the correct comparison to make and why.

    I bring this up because I recall that given a matrix representing the density matrix of a bipartite quantum system, determining whether it represents an entangled or separable quantum state is in general NP-Hard, but IIRC there exist semi-definite programming techniques to get the answer probabilistically in polynomial time. The point is that in that case there's a big gain for accepting an answer that will be wrong every once in a while. I was just curious if settling for an approximate answer in solving linear systems changes the complexity of that problem drastically as well.

    --
    "You call it a new way of thinking; I call it regression to ignorance!" -- Operation Ivy
    1. Re:Comparing Apples to Apples by BZ · · Score: 1

      Of course any quantum computing algorithm (including Shor's) has the same issue.

      In practice, once the probability of the answer being incorrect is smaller than some threshold (e.g. the probability of the classical computer giving a wrong answer due to cosmic rays) it really doesn't matter that you're using a probabilistic algorithm.

    2. Re:Comparing Apples to Apples by ASkGNet · · Score: 1

      Let's say the probability is 1/2. The solution to the system can be verified in polynomial time. If the solution is incorrect, run the algorithm again.

      After you run it N times, the probability of error is 1/(2^N), and you only wasted polynomial time on verification. Clearly, when your probability of error is smaller than the cardinality of possible outcomes, the algorithm will perform as designed in a sane amount (polynomial) of time.

    3. Re:Comparing Apples to Apples by internic · · Score: 1

      It's true that something like Shor's algorithm is probabilistic, and so, yes, you're always sort of comparing apples to oranges. So in that situation you can define a probability distribution on the amount of time it will take to get the correct answer. To compare apples to apples you simply compare some number like the mean time for solution, or the 95th percentile longest time for solution (there's also the question of best- and worst-case scenarios) for the two algorithms. If the classical algorithm is deterministic, it's probability distribution is just simpler. I assume that in the case of factoring there's no faster non-deterministic classical algorithm so that it's a moot point.

      In this case it looks like they're talking about solving the system to within accuracy epsilon and comparing that to solving exactly, which seems a bit different than the question of solving exactly but sometimes being wrong. Mostly, in this case you're "wrong" most of the time but only a little wrong, and you don't go back and correct it. So my question is whether in this case there is a faster classical algorithm if we let it also get the answer only to within epsilon; this is the classical algorithm we would wish to compare to.

      So, I think you're right that you're always sort of comparing apples to oranges, but it seems like here we're doing so to an unnecessary degree. In all likelihood, relaxing the condition on the classical solutions doesn't admit any known faster solution, and the authors just assumed the reader knows this. But I don't know it, and I am hoping someone on /. does.

      --
      "You call it a new way of thinking; I call it regression to ignorance!" -- Operation Ivy
    4. Re:Comparing Apples to Apples by aram.harrow · · Score: 4, Informative

      This is a great question. Here's how I like to think about it: If A is a stochastic matrix and b is a probability distribution that we can sample from, then given a few assumptions, we can sample from Ab efficiently. This is more or less the idea behind so-called Monte Carlo simulations, which are a tremendously useful tool in classical computing. However, we don't know how to get sampling access to A^{-1} b. Our algorithm gives us something like sampling access to A^{-1} b. Not exactly, because we're talking about quantum amplitudes, rather than probabilities. But more importantly, taking the inverse can make a sparse matrix dense, and (as we often see for problems admitting quantum speedups) sampling-based approaches to computing it fail because the samples have alternating signs.

    5. Re:Comparing Apples to Apples by internic · · Score: 1

      I'm not sure the number of possible outcomes has anything to do with it. These quantum algorithms can in principle give the same wrong answer over and over again (though this is extremely improbable), so it's not like you exhaust the set of wrong answers or something. In any case, it is certainly true that you can put a probability distribution on the time it will take the algorithm to get the answer, and you ask how long it will take to get a solution on average or that it will take less than T operations 99.999% of the time. Clearly, if you're comparing a polynomial to an exponential time growth, at any level of confidence the quantum polynomial algorithm will win asymptotically.

      But that's all beside the point, because my question is really more about the classical problem. By my (admittedly not thorough) reading, it looks like all they're requiring of the quantum algorithm is to find the solution vector up to an relative error epsilon in the 2-norm. (i.e., it appears epsilon is a distance in the vector space, not a probability) To wit:

      we can approximately construct |x> = A^1 |b>...
      ...then our residual state (up to relative error O(t_1^2 kappa^2 )) is A^-1 |b> = |x> . Taking t1 much less than 1/kappa gives a good success probability.

      What I'm wondering is whether similarly relaxing the requirements on the classical computation (so that you only require such an approximate solution in the same sense, not an exact solution) will reduce the classical computational complexity of the problem significantly.

      --
      "You call it a new way of thinking; I call it regression to ignorance!" -- Operation Ivy
    6. Re:Comparing Apples to Apples by aram.harrow · · Score: 1
      What I'm wondering is whether similarly relaxing the requirements on the classical computation (so that you only require such an approximate solution in the same sense, not an exact solution) will reduce the classical computational complexity of the problem significantly.

      We plan to soon update our arxiv post to explain that the matrix inversion problem (with the parameters we consider) is BQP-complete, meaning it is as hard as anything that quantum computers can solve in polynomial time. This is strong evidence that classical computers need exponentially more time to solve the problem in general. Of course, there may be special cases, some of practical interest, where good classical algorithms exist.

  48. Re:not able to be used == not useful by Ambitwistor · · Score: 1

    If you do that, I think you're turning Computer Science from having been a branch of Mathematics into some completely different animal.

    Algorithmic complexity theory has always depended on what you define a "computer" to be. An algorithm is an algorithm, but its space and time requirements require assumptions about what is executing the algorithm. That doesn't mean that the algorithm is non-mathematical. It means it uses different assumptions about what a computer is. That doesn't make quantum computing any less mathematical than classical computing. It just makes the mathematics different.

    It is not mathematically proven or provable (beyond the proof that the most probable state is the desired result).

    Non-deterministic algorithms have probabilistic correctness guarantees, not absolute guarantees. That's one of the reasons why they're theoretically interesting to computer scientists.

    And while that's perfectly good and useful for doing calculations and getting results, it is not a new kind of math, or any kind of math.

    Of course it is math; just read any paper on the subject, or the lecture notes I linked. The mathematics of quantum algorithms is different from the mathematics of classical algorithms. That's why they have different computational complexities.

  49. Re:not able to be used == not useful by BZ · · Score: 1

    I don't see a big difference in mathematical content between "if you start with this state, and perform these transformations you will have this other state" and "if you start with this state, and perform some transformations, then you will have this other state".

    Those are descriptions of classical and quantum algorithms, basically.

    Now the only question is how to translate the final state into "the answer". In the case of classical algorithms the translation is usually very simple. In the quantum case, the final state is a probability distribution, and "the answer" is the mean of the distribution.

    That's if you're talking about the computer science aspect of the whole thing. If you're talking about actually building a computer, that's a different story, and you need to worry about your distribution's standard deviation, etc, but let's not mistake that for the theory part.

    I should note that there is a long tradition of probabilistic algorithms in classical computer science, by the way.

    I should also note that probability theory is generally considered "pure math".

  50. Re:not able to be used == not useful by SleepingWaterBear · · Score: 1

    Third, you're wrong. Lets take a 65536 bit long encryption key, the product of two very large primes. Lets factor them! The best known deterministic algorithm is going to take longer than the universe will last. But I bet it takes well under a second to check an answer for correctness! Let's say you have a quantum "algorithm" Q. You are correct, you can't prove Q(key) will produce the correct factorization. But you can CHECK it in only a second. So, run Q(key) until your check passes. There, that's an algorithm by your definition. You just used math to prove that if you run your quantum + classical hybrid computer on that input, it will always output the correct result.

    Well, technically all we know is that it will never output an incorrect result. It could just continue to run until the sun goes nova, though of course this result is vanishingly improbable. Not that I disagree with your main point at all, I just like nitpicking!

    That said, I think what the GP is concerned about is that with traditional algorithms you can, if you have enough time and paper, sit down and follow the same steps the computer does to do the calculation by hand. What he doesn't realize is that Quantum algorithms can also be performed on pencil and paper, they would just be extremely inefficient without the particularities of the hardware of a quantum computer.

  51. Re:not able to be used == not useful by cnettel · · Score: 1

    That's like saying GPGPU is useless, just because GPUs are not very useful for serving web content, or files, or being used for databases (what fills most datacenters). They are great for some (not all) HPC applications, though. A practically useful quantum computer, even if unbelievably expensive, would still be useful for those things that quantum computers do exceedingly well. In the 50s, a small firm would never get a computer to replace accountants. Government agencies and some companies would still get them for the most demanding computation tasks of the time. As a quantum computer moves us firmly outside the von Neumann paradigm, and to some degree outside Turing as well, we can't just look at the cost and whether large deployments are feasible, because even one machine will be useful for those tasks that no machine, or only a million or more machines, can do within a realistic amount of time today.

  52. Re:Thoughts? by Anonymous Coward · · Score: 1, Funny

    Is it white? No. Is it black? No.

    Actually, it's the next president.

  53. Re:not able to be used == not useful by z-j-y · · Score: 1

    At the very least it can be regarded as pure math, and it can be quite interesting.

    On the other hand, the fundamentals of quantum mechanics are still very muddy, quantum measurement is very un-well-defined, nobody has any idea how many qubits you can put together before the system becomes a decoherent macroscopic classical system. Are quantum computers even *theoretically* possible? Or are there some basic laws of nature that deprive Human the access to the computing power that Universe obviously posesses?

  54. Weather? by Anonymous Coward · · Score: 0

    Would weather simulation be an applicable problem?
    Because if they could use this to predict tomorrow's weather even 5% more accurately that'd be nice.

  55. Quantum Algorithm Zoo by n01 · · Score: 1

    Here is a long list of problems that have superpolynomial i.e. more than polynomial speedup compared to classical computation. Even though the author doesn't think so many do have practical applications.

  56. Re:not able to be used == not useful by TerranFury · · Score: 1

    "All cats are gray in the dark."

    (Franklin on the advantages of older women. He wrote a whole essay on the subject. His basic thesis was that the "juices" -- I think that was his word -- move down in the body as a woman ages...)

  57. It IS bogus (probably) by l2718 · · Score: 3, Interesting

    The weak point to me is where they "map A to a quantum-mechanical operator". They completely ignore the timing of this step, which amounts to assuming assuming that multiplication by A takes time O(1). With that assumption I'm sure you can do linear algebra blazingly fast.

    1. Re:It IS bogus (probably) by aram.harrow · · Score: 2, Interesting
      This is explained in the technical appendix. We assume that A has at most s non-zero entries per row, and that A is stored in a data structure that efficiently answers "return all non-zero entries in a row" queries. For example, an array of lists would work. Our run-time then has an O(s^2) dependence.

      Basically we need to assume random-access memory. There has been some preliminary work on models for quantum RAM, some of which we cite in our paper. But as a sign that the model isn't too powerful, we know that classical computers with RAM are not exponentially faster than weaker models, like single-tape Turing machines or 1-D cellular automata.

      Alternatively, there might be a short algorithm that generates the entries of A. In this case, we could simply use it as a subroutine without having to make any assumptions about the quantum computer's architecture.

  58. Re:Thoughts? by Anonymous Coward · · Score: 0

    Survival of the fittest... these jigaboos know it, and KNOW that they are inferior to us, and will die out eventually

    i know jigaboo is a racial slur, but it always makes me giggle. jigaboo sounds like a pokemon.

    "jigaboo, i choose you! use your spear chuck attack!"

  59. Re:not able to be used == not useful by Anonymous Coward · · Score: 0

    BTW, I don't have "heroes", but if I did, Franklin would be my nr 1.

    Well don't bother, Sylar just killed him in the last episode.

  60. Dammit! by actionbastard · · Score: 1

    Where is the on-line version of the 'Quantum Linear Equation Solver' built with hookers and blackjack?

    --
    Sig this!
  61. Re:Thoughts? by Anonymous Coward · · Score: 0

    TELL ME IF I AM WRONG. PLEASE! I DO NOT LIKE BEING HATEFUL, AND I DO NOT WANT TO BE HATEFUL ANYMORE, BUT THE EVIDENCE IS JUST OVERWHELMING. I CANNOT HELP IT.

    You're wrong. When you're strolling through the hood for whatever reason and your pasty overweight white ass is quivering in fear and disgust you might just get mugged for the hell of it. Grow some balls, lose some weight, carry yourself like a man and not some pussy and you can go wherever you want.

  62. I need no solver! by Mister_Stoopid · · Score: 1

    Like all real mathematicians, I solve my quantum linear equations by hand.

  63. Re:Thoughts? by twitchard · · Score: 1

    Except there are white urban thugs too... Don't even bring race into the matter. Direct your hate at thugs, not a race.

  64. Encryption? by Anonymous Coward · · Score: 0

    Couldn't this break certain encryption schemes? Or am I confused here?

    Maybe I was thinking of discreet logarithms or something else instead.

  65. Where are mod points when you need them? by mosel-saar-ruwer · · Score: 1


    Also, I have read in my life thousands of published peer-reviewed articles, and many of them contain incredible imbecillities where I have to question whether all the reviewers were high on hallucinogens. Very very high on hallucinogens.

    Could someone mod the parent up +1 whatever [insightful, informative, funny - really, a "tragicomic" mod point would be most appropriate here].

    Back in the day, Goro Shimura used to say that something like 50% of all published mathematics is simply rank nonsense, but these days, I'd say that the proportion is closer to 99%.

    1. Re:Where are mod points when you need them? by blind+biker · · Score: 1

      I don't read maths articles. My field of research is in nanosciences, materials science, physical chemistry etc. etc. (chemistry is really quite important for my research on multiple levels). In the kinds of articles I read, the nonsense is easy to spot - for me. I'm quite pedantic (or anal, if you prefer) when it comes to scientific rigour.

      I take it you're a maths researcher? I just had a nice mini-thread/discussion with a maths grad student, he tells me it takes quite a long time to read a maths article. I believe him. The articles I read, I can read easily one or two per day, and when I'm writing something then that goes up to three or more(though I don't go as deep into the material). I've written two reviews (both unpublished, as far as I know - one is part of an inter-project initiative, so the collective work may have been submitted somewhere), and the amount of articles per day was just simply ridiculous. It's harder to spot the BS when you read them at that tempo, I admit. But when I take my time, I find some awful nonsense quite often - and really, I just imagine these two, allegedly world-class experts in the subject, reading carefully (???) through this paper and giving the nod to this steaming pile of ****, and I just don't get it. I think reviewers should be held accountable in some way.

      --
      "The agriculture ministry is not in charge of Gundam" - Japanese ministry official.
  66. Re:not able to be used == not useful by MoellerPlesset2 · · Score: 1

    When Turing first described a computer (a turing machine), it was essentially a mechanism where you put a tape in a certain state, manipulate it according to certain rules and in the end you get the tape in another state containing the "result" of your computation. What was so interesting about it it that it was theoretically possible to build a machine that would be able to do the manipulations automatically.

    You miss the point entirely. Turing's machine _always_ gave the same result for the same data and could be mathematically proven to do so.
    You can NOT predict the result of a quantum 'calculation'. You can predict the _probabilities_ of the various possible results.
    This abandoning of what is mathematically provable is not a casual thing.

  67. Re:not able to be used == not useful by FrangoAssado · · Score: 1

    Ah, so your problem is not with physics, but with probability.

    The thing is, there's no "abandoning of what is mathematically provable" in studying probabilistic algorithms. Computer science has studied for decades complexity classes like BPP (bounded-error, probabilistic, polynomial time) which contains many useful algorithms, like for instance the Miller-Rabin primality test, which is used by OpenSSL to check if a number is prime.

    So, whether you like it or not, it's already part of computer science.

  68. Quis custodiet ipsos custodes? by mosel-saar-ruwer · · Score: 1


    I think reviewers should be held accountable in some way.

    Quis custodiet ipsos custodes?

    The truth of the matter is that the problem is inherently intractable.

    If you have good people writing papers, then you will get good papers.

    If you have lousy people writing papers, then you will get lousy papers.

    What people need to realize [and what almost all people in the grant-writing racket lack the strength of character to admit] is that most published "research" is simply false.

    And if to "false" you were to add "trivially tautological or essentially meaningless" then you would have classified almost all of published "research" nowadays.

    But the grant-writing racket is very powerful politically, and the milk from the teat of that sow tastes oh so good...

    1. Re:Quis custodiet ipsos custodes? by blind+biker · · Score: 1

      By grant-writing racket, do you mean grant-application-writing racket, or grant-granting (uh, what's the verb, help me out..) racket? Two separate sets of people. That said, I agree with the general idea of your post. Though I strongly disagree that almost all published research is either false or "trivially tautological or essentially meaningless". There's plenty of good stuff out there. At least in natural sciences.

      C'mon now - "almost all"? You didn't really mean it, did you?

      --
      "The agriculture ministry is not in charge of Gundam" - Japanese ministry official.