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Math Supercomputing Science

Making Cesium Atoms Do a Quantum Walk 117

Posted by kdawson
from the like-a-perp-walk-only-without-the-cameras dept.
An anonymous reader recommends an Ars Technica account of a breakthrough in efforts toward quantum computing. German scientists have managed to get cesium atoms in a state called a "quantum walk": basically a superposition of all the possible states of a particle. "Quantum walks were first proposed by physicist Richard Feynman and are, in terms of probability, the opposite of a random walk. A random walk might be modeled by a person flipping a coin, and for each flip he steps left for heads and right for tails. In this case, his most probable location is the center, with the probability distribution tapering off in either direction. A quantum walk involves the use of internal states and superpositions, and results in the hypothetical person 'exploring' every possible position simultaneously." In the abstract of the paper from Science (subscription needed for full-text access), the researchers say: "Our system allows the observation of the quantum-to-classical transition and paves the way for applications, such as quantum cellular automata."
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Making Cesium Atoms Do a Quantum Walk

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  • Do we have a plan for when one day, our current methods of encryption all become breakable at once?

    • Re: (Score:3, Funny)

      by Killer Orca (1373645)

      Do we have a plan for when one day, our current methods of encryption all become breakable at once?

      What a wasted opportunity, your first post is supposed to say "First post, or is it?"; well I suppose you can always wait for the next quantum computing breakthrough.

      • by Anonymous Coward on Monday July 20, 2009 @11:03PM (#28765777)

        Do we have a plan for when one day, our current methods of encryption all become breakable at once?

        What a wasted opportunity, your first post is supposed to say "First post, or is it?"; well I suppose you can always wait for the next quantum computing breakthrough.

        "3very p0st" would have been an acceptable alternative, in my opinion.

      • by SEWilco (27983)
        His first post state would have collapsed had he observed it. It was only by acting without looking that he preserved the state.
      • by sjames (1099)

        What are you talking about, that's exactly what it said here. I guess you lost the quantum coin toss.

    • Re: (Score:3, Funny)

      by slickwillie (34689)

      It could just be a lot of quantum talk.

      • by tenco (773732)
        Quantum talk? Is this like small talk, only more fuzzy?
        • Re: (Score:3, Funny)

          by Linker3000 (626634)

          No, you say every possible permutation of your sentences simultaneously and then when the other person hears this they instantly forget what they have heard.

    • by fuzzyfuzzyfungus (1223518) on Monday July 20, 2009 @11:03PM (#28765781) Journal
      A massive cash advance drawn against every credit card in the world, and a castle made of pure unicorns in a country with flimsy extradition treaties?

      That's my plan, anyway.
      • In a country? With that much cash, you can have your own country. With blackjack. And hookers!

        Aaand a huge military, making the country survive in the first place.

        Just be sure to transform all that money into gold. Because it will be worth shit, when nobody accepts it anymore.

    • Re: (Score:3, Insightful)

      by TiberSeptm (889423)
      A working AND cost effective quantum computer capable of decrypting your pr0n is still a ways off.

      If someone wants to spend that kind of money and resources to get you, then it doesn't matter what kind of decryption they have. If they can't ruin you by decrypting your secrets then they can just make something up. Fake compromising information is going to be the easier way to go for long enough that you shouldn't have to worry about it. I mean a planted local news story or thorough facebook+myspace+bl
      • by XanC (644172)

        What about all the backup tapes or laptops that are stolen, but we don't worry about it because the data was encrypted?

        Today we don't consider that data to have been compromised. But in the not-too-distant future it could be cracked instantly.

      • Re: (Score:3, Insightful)

        It's probably less about people "getting you"(I suspect that, today, relatively few people are actually being protected from a hostile superior power by the strength of their crypto) and more with things like the breakdown of electronic commerce security, the spoofability of cryptographic signatures(Goodbye SSL) and new difficulties in secure authentication(SSH would be about as useful as telnet).

        If a superior power simply wishes to ruin you that is, as you say, typically easy without any codebreaking. P
        • That, and the degree of effort required and risk is enough to make it worth their while. It's kind of like locking your car. If someone were to create a device that allowed someone to pass effortlessly through car windshields that doesn't automatically mean the device would be all that practically useful to a car thief. If it cost millions of dollars and required liquid nitrogen or helium cooling, then you're not going to see a rash of car thefts using said device, despite it appearance as a perfect tool
          • So we have another ten years left?
          • Encryption is nothing like a car lock. The cheap thieves aren't the ones we have to worry about with regard to encryption. Governments in fact are quite willing to spend many billions of dollars for a device which can crack citizens' encryption in order to help them control those citizens more effectively. Combine that with the internet -- a vast system of networks through which large amounts of data are piped and which, unfortunately, happens to contain large several bottlenecks at which governments can st
        • by plnix0 (807376)
          One important consideration you omit is that the superior power can't destroy everyone because their power depends on most people either supporting them or being rather apathetic about them. So the super power desires the means to acquire enough information about everyone to decide whom to eliminate. Now that information is (effectively) not encrypted? Their job just got easier.
      • by sconeu (64226)


        If someone wants to spend that kind of money and resources to get you, then it doesn't matter what kind of decryption they have. If they can't ruin you by decrypting your secrets then they can just make something up.

        Ob XKCD [xkcd.com]

      • by Kagura (843695)

        such as in an aluminum pole

        Another festivus miracle!!

    • I wouldn't worry. As long as there are NP problems that take extremely long unless you have a hint, we have encryption methods.

      • by XanC (644172)

        But all the encrypted data in the wild that's considered safe because it's encrypted would have to be considered compromised, right?

        • by trum4n (982031)
          Once they build, then harness this computer, we still have to wait 10 years for them to figure out how to program it without reading data, after all, once you observe the data, it will be changed. It's kinda like Safely Remove in Windows XP.

          By using Plug and Play technology as it was intended, you have corrupted all your data. They invented a technology, and couldn't implement it, so it's useless, and some day they will figure it out.
          • by Engine (86689)
            Not really. You set the initial state and read out the final results, which is in principle straightforward. The only thing you are not allowed to do is to try to measure the state in between.
        • Well, if you have used encryption for several years now, you probably made a move from 128bit over 512bit to 2064bit key size. For some encryption methods quantum computing will just be another step, but a really big one.
          For others, quantum computing may "solve the decryption" directly by the different approach (superposition, probabilistic calculations).

    • by smaddox (928261)

      First of all, only public key encryption algorithms based on factoring would be broken. Others would still be strong (until a quantum algorithm was written to break them).

      More importantly, properly applied one-time-pad encryption would still be unbreakable. I wouldn't be surprised if certain military/intelligence organisations were already using one-time-pad's that were distributed before missions (on DVD or HDD).

      It is also worth noting that public-key encryption is already breakable at typical bit-strength

      • by Engine (86689)
        Quantum key distribution is already available commercially, see for example:

        http://www.idquantique.com/

        Quantum computers do still have a very long way to go before they are useful for anything else than factorizing very small numbers. The last record I heard of was 15, which was already quite a while ago, but I find it unlikely that they have managed to do any significant improvements since then.
    • Don't start measuring your quantum particles just yet.

      We don't know that a quantum computer will be able to break every encryption scheme we have. We have the famous open problem of whether P=NP. (I'd bet against.) For those who don't know, P is the set of all problems solvable in polynomial (that is, relatively quick) time, and NP is the set of all the problems solvable in polynomial time if only it was practical to try every possible solution in parallel, or there was some fast (polynomial time or

    • I think the general plan is to lament how this could be possible, despite the fact that everyone ignored the possibility.

    • Simple Re-encrypt using the same quantum tech you are worried about.
      The issue is more of a case of which country gets there 1st.
      My money is on China
    • Re: (Score:3, Funny)

      by Linker3000 (626634)

      ROT13

    • by JSlope (1180805)
      Try to google for Post-Quantum Cryptography, only Public Key Cryptography is in danger, traditional symmetric algorithms are not affected much by quantum computers. There are public key algorithms which might be resistant to quantum computing, but only time will tell for sure :)
  • by wdef (1050680) on Monday July 20, 2009 @10:30PM (#28765581)
    "And that geodesic is not shtraight either. Sho's I'll just superimpose my states back in da car and be on my way ..."
  • by BadAnalogyGuy (945258) <BadAnalogyGuy@gmail.com> on Monday July 20, 2009 @10:31PM (#28765583)

    Cesium is an interesting element in that it is perfectly reliable. While some elements will differ in atomic weight due to random changes in their electron sphere radii and the number of neutrons in the nucleus, Cesium has a perfect vibration rate independent of external stimuli. It is so regular and reliable, in fact, that we base our entire measurement of time on clocks composed purely of Cesium.

    If, as is demonstrated here, Cesium can be used to explore multiple quantum states in a regular and reliable fashion, the possibility to build quantum computers and automata based on Cesium goes way up. Not only would these "computers" function better than our current computers, they would always be 100% perfect (unless Intel manufactures them, lol) and not prone to error or breakage.

    • by Engine (86689)
      There is different isotopes of Cesium too, it is just that they have chosen one specific isotope for the measurements. In that regard Cesium isn't unique at all. I don't know what you mean with the "random changes in their electron sphere radii", but I don't see how Cesium would be different from other alkali elements in that regard.

      The last part of your comment is just false. There are problems that quantum computers would be able to solve that you can't solve with any practical classical computer, but the
      • There is different isotopes of Cesium

        Is one of them spelled with an a?

        • by Engine (86689)
          If you are Brit, they all are.
          • Nope, we don't fill balloons with haelium.
            • by Engine (86689)
              I know that you are deliberately obtuse, but helium isn't an isotope of cesium.
              • Instead of driving your 98 litre Hummer thirty yards to the burger joint three times today, why don't you stay in your trailer and learn to spell Aluminium properly?
                • by Engine (86689)
                  You don't even know how to troll properly. I'm Scandinavian, and the only reason I chose to spell Cesium in this way was because that was how it was spelled in the post. When in Rome... You have now not only proved your illiteracy, but also your stupidity by your unfounded conclusions, you inbred gnome.
  • by DigiShaman (671371) on Monday July 20, 2009 @10:44PM (#28765669) Homepage

    As far as I know it, we have three main instruction sets. Integer, Floating Point, and Vector (SSE, MMX..etc). Would it more likely be that we would end up with the forth set being Quantum? Or, would it be possible to have an entire CPU quantum based?

    • by BadAnalogyGuy (945258) <BadAnalogyGuy@gmail.com> on Monday July 20, 2009 @10:49PM (#28765701)

      To your first question: Yes. There would be a new instruction set called "Eigen". It would contain all possible values simultaneously. The interesting thing about such a value is that it could be used to determine the correct value of any problem simply by casting it to the appropriate data type. Since the other instruction sets can only contain a single value at any time, the correct value (for our universe) is automatically saved in the other data type.

      For your other question: Yes and no.

      • For your other question: Yes and no

        *smacks my forehead*

        Of course!!! I would need a quantum CPU to get the correct answer because "Yes and No" are still undetermined. Now I understand ;)

        • With a quantum computer, the answer can be a superposition of yes and no states.
          • by weicco (645927)

            What about maybe?

            • by WarJolt (990309)

              Nope.

            • by szo (7842)

              That's what superposition means, just less fancy :)

              • No. Maybe corresponds to a 1 probability of something being true. In a quantum computer, the probability of true is 1 and the probability of false is 1, thus the "yes and no".
                • by szo (7842)

                  No. Quantum or not, the sum of the probabilities of all possibilities still 1.

              • Re: (Score:3, Informative)

                by radtea (464814)

                That's what superposition means, just less fancy :)

                Nope, and this is a good straight line for my futile quest to explain something about quantum weirdness, because it is precisely the difference between "maybe" and "superposition" that makes life interesting for a quantum mechanic.

                "Maybe" is a classical concept. If we see a cat get into a box, and then there is a sudden yowling and howling from the box, and you ask me, "Is the cat ok?" and I reply, "Maybe" we are talking about a classical situation, in whi

                • by radtea (464814)

                  Man, I sure screwed up that last sentence, which should read:

                  "...when the natural expectation would be that after a measurement had taken place we would be aware of the measurement apparatus as being in an incoherent superposition of orthogonal states."

          • by Engine (86689)
            Your answer will never be a superposition. You prepare the initial steps into superpositions and then use superpositions in the calculations, but you will get a definite answer in the end. Of course you can run your computer many times and if your programming is such then you can get different answer for each run even if the inputs were the same.
        • by WarJolt (990309)

          It's yes and no. We determined it to be both simultaneously.

      • ...the correct value (for our universe) is automat... 42

      • "The interesting thing about such a value is that it could be used to determine the correct value of any problem simply by casting it to the appropriate data type."

        This is incorrect. Determining the superposition's state won't give you the correct answer. It will give you a random answer from all of its possible states -- weighted by the chance of that being the right answer. This makes quantum computing much trickier.

        http://scottaaronson.com/blog/?p=208 [scottaaronson.com] is a great article if you want to understand how s

    • It might be inaccurate to call any quantum computer an "entire CPU" even when it is the processor of interest in a given system. While they are currently more of an experiment that is being observed and manipulated with the aid of traditional computing devices and lasers, even when they are more refined they are more likely to fill the roll of a sort of co-processor. This is because although they theoretically do certain tasks far better than a traditional processor (or, in the case of integer factorizati
    • by SEWilco (27983)
      answer = (string) ( eigen(! NULL) )
      • by SEWilco (27983)
        Oops, I had the answer and forgot to print it. I should have created a debugged program. program = (debug) ( eigen( ! NULL ) ) run( program )
    • by intx13 (808988)

      As far as I know it, we have three main instruction sets. Integer, Floating Point, and Vector (SSE, MMX..etc). Would it more likely be that we would end up with the forth set being Quantum? Or, would it be possible to have an entire CPU quantum based?

      Quantum computation is unlikely to replace classical computation. There are certain problems at which quantum computation excels (problems that involve period-finding in some way, shape, or form) and many problems that it doesn't excel at (anything else).

      A quantum encryption co-processor is most likely the first way in which quantum computation will reach the classical computing world, and for physical reasons (you need an actual quantum communication channel to attach to) I wouldn't expect it on your

    • As far as I know it, we have three main instruction sets. Integer, Floating Point, and Vector (SSE, MMX..etc). Would it more likely be that we would end up with the forth set being Quantum? Or, would it be possible to have an entire CPU quantum based?

      Sure it would. Modern processors do things with several bits at once (like 32 or 64 bits integers, floats that you mention). Quantum computer calculates with several quantum-bits (so-called q-bits) at once, using their entanglement together with quantum evolution and a measurement on the evolved q-bits. This has nothing to do with some word Eigen that other posts are mentioning, because we can simulate quantum computers classically, so Eigen is not necessarily operation that only quantum computer does--w

  • by gcnaddict (841664) on Monday July 20, 2009 @11:30PM (#28765915)
    Theoretically speaking, if we could get, say, an entire ship and all of its inhabitants to do this "quantum walk"...

    wouldn't we be well on our way towards creating an improbability drive?


    I'm probably hugely stretching this beyond what it means.
    • by intx13 (808988)

      Theoretically speaking, if we could get, say, an entire ship and all of its inhabitants to do this "quantum walk"...

      Ah, but you can't. Quantum mechanics applies only to quantum particles, not big honking spaceships. Of course nobody has integrated quantum mechanics with classical mechanics yet, so you never know ;)

      The thing is, quantum mechanics is just a mathematical system that seems to work pretty well. As in, it predicts what really tiny things will do extremely well. When a quantum particle takes on different states at a time, that is a mathematical concept that, when applied, produces a result that agrees w

      • by shermo (1284310) on Tuesday July 21, 2009 @12:17AM (#28766143)

        Quantum mechanics applies to large particles. Classical mechanics are merely an approximation of quantum mechanics when applied to large particles.

        Wikipedia to the rescue

        http://en.wikipedia.org/wiki/Correspondence_principle [wikipedia.org]

        • by Anonymous Coward

          Actually Quantum Mechanics applies to individual atoms regardless of size. Classical mechanics corresponds to the mathematical limits when the number of particles becomes large, i.e. you take the mathematical constructs of quantum mechanics and extrapolate to the number of particles being infinity and you come up with the mathematical construct for Classical Mechanics.

          So Anpheus is correct. How do I know this? Well, I have a Ph.D. in Physical Chemistry.

      • by Anpheus (908711) on Tuesday July 21, 2009 @12:27AM (#28766195)

        From what I've read on the issue, such as Feynman's books and other novels targeted toward those of us who do not have a complete grasp of quantum mechanics, you are wrong.

        Caveat emptor, this is merely what I've read:

        Classical mechanics as explained by Feynman were the result of the sum of all possible histories, among other interpretations. Regardless of one's interpretation, Feynman and others found that as you crunch the math for larger and larger quantities of particles, the results closer and closer approximate what we think of as classical physics. As a result, classical physics is an approximation of quantum mechanics, which is a theory of how the universe really works.

        • by mea37 (1201159)

          ...well, yes, until you get to really large (or fast) scales, at which point QM comes into direct conflict with relativity.

          I've heard of recent attempts to reconcile the two, but last I heard there was still no universally accepted answer.

      • Re: (Score:2, Informative)

        by mindbrane (1548037)
        If you download the 2009 intro to General Principles of Chemistry from the mit OpenCourseWare offerings you'll get some pretty good stuff on the relationship of Quantum Mechanics and Classical Physics. IIRC the wave descriptions of big league fast balls are used (lectures 4 & 5). I'll leave it there as any attempt by me to go into the particulars will go high and outside.
      • by 3waygeek (58990)

        Quantum mechanics applies only to quantum particles, not big honking spaceships.

        Not quite a spaceship, but quantum tunnelling has been shown to apply to non-quantum particles [trygve.com].

    • by JoCat (1291368)

      If we had a quantum pirate ship we could make people walk the Planck.

  • "Left! Right! Left a wife and seventeen children in starving condition with nothing but gingerbread left! Left!"
  • with me? We can explore every possible position simultaneously.
  • Please do not write further articles about quantum computing. This one was both factually inaccurate and unreadable. :P

  • fall in the same class of problems w.r.t to Quantum computing now?
    • The answer is: we don't know. Noone's devised a polynomial time quantum algorithm for any of the NP-complete problems yet.
    • by AllureFX (1602331)
      Whether polynomial time or not, "hypothetical person 'exploring' every possible position simultaneously" does sound a lot like nondeterministic TM.
  • In other news, two Cesium atoms were shot dead by Crip gang members in East Los Angeles. Eyewitnesses report the two Cesium atoms were seen performing the Quantum Walk at the time of the shooting.
  • Reading /. stories that include the phrase "...first proposed by physicist Richard Feynman..." make my head explode.
  • At my age, I have trouble with a duck walk.

  • I'm imagining something like a cross between Mancini's Baby Elephant Walk and the Hamster Dance

  • You can get the full article from the arxive:

    http://arxiv1.library.cornell.edu/abs/0907.1565 [cornell.edu]

    It is really a beautiful experiment. I have never seen such a demonstration of how deterministic the propagation of the wavefunction is. By simply running the experiment backwards they manage to get the atom to go back to it's initial position in the walk.

  • lt's not particularly quantum, is it? I'm afraid that the Ministry of Quantum Walks is no longer getting the kind of support it needs. You see there's Defence, Social Security, Health, Housing, Education, Quantum Walks ... they're all supposed to get the same. But last year, the Government spent less on the Ministry of Quantum Walks than it did on National Defence!
  • When talking about quantum computing, don't forget that someone has to write the programs. If you thing programming in a SIMD (Single Instruction Multiple Data) is difficult, try SIID (Single Instruction, Infinite Data).

    Also remember that there are a few REALLY hard problems to solve before we can have a quantum computer compute anything. For example, to factor a key, you have to have two 'registers' and somehow get them to be the superposition of all primes less than the key value. That is, all non-primes

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