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Supercomputing Science

Research Team Makes Quantum Computing Progress 125

Posted by ScuttleMonkey from the zero-one-two dept.
Timogen writes to tell us Wired is reporting that a research team is reporting that they have found a way to "controllably couple qubits" bringing us one step closer to quantum computing. "In classical computer science, bits -- or binary digits -- hold data encoded as ones and zeros. In quantum computing, data is measured in qubits, or quantum bits. As such, a qubit can have three possible states -- one, zero or a "superposition" of one and zero. This unique property theoretically makes quantum computing able to solve large-scale calculations that would dwarf today's supercomputers. But qubits in isolation are not very useful. It's only when they can be connected to one another that large-scale processing becomes possible."
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Research Team Makes Quantum Computing Progress More

Research Team Makes Quantum Computing Progress

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  • You know what else was measured in qubits? (Score:5, Funny)

    by Anonymous Coward on Monday May 07, 2007 @03:22PM (#19025637)
    The Ark. That's right: Noah's Ark.

    • Re: (Score:2, Funny)

      by holden caufield ( 111364 )
      Riiiiight. What's an ark?

    • Re: (Score:2, Funny)

      by MindKata ( 957167 )
      "The Ark. That's right: Noah's Ark."

      What so the quantum state animals were both inside and outside the ark, until he counted them?

      I guess he must have also had some Schrödinger Cats onboard as well then.

    • Re: (Score:3, Funny)

      by Afecks ( 899057 )
      I'm not sure if you realize it but none of that stuff actually happened.

      Sorry to be the one to break it to you...

      • Re: (Score:3, Funny)

        by Alsee ( 515537 )
        Damn atheists.

        I bet you don't even believe in talking snakes either.

        -

    • Re: (Score:1)

      by Tablizer ( 95088 )
      The Ark. That's right: Noah's Ark.

      So, how many arks can fit on the head of a pin?
           

  • Three states? (Score:5, Informative)

    by Anonymous Coward on Monday May 07, 2007 @03:22PM (#19025647)
    Qubits can have an infinite number of states between 0 and 1 (inclusive). "Superposition" does not describe a single state, it just means that it's somewhere in between.

    • Re: (Score:2, Interesting)

      by darkwing_bmf ( 178021 )
      Would this not describe an analog computer?

      • Analog vs Quantum (Score:2, Interesting)

        by Anonymous Coward
        Kind of. But then you can still create qubits in entangled states, like, upon measuring two qubits you get always one "1" and one "0" , but you don't and cannot know which is which until you measure. You can't do that with an analog computer.

      • Re: (Score:3, Informative)

        by Stevecrox ( 962208 )
        Modern computers are analogue, in fact all digital electronics are analogue. We call it digital because threshold voltages are chosen, so if a bit's voltage was 1.2volts it would represent a '0' bit, however if its voltage increased to 1.8volts the computer will see it as a '1' bit.

        You can use tri-state in modern computers (and I believe it is used) the problem comes from interference, modern microprocesser's already battle quantum effect and bulk effect, adding anouther layer make things much harder.

        Quantu

        • Re:Three states? (Score:5, Interesting)

          by AKAImBatman ( 238306 ) * <akaimbatman AT gmail DOT com> on Monday May 07, 2007 @03:56PM (#19026227) Homepage Journal
          Try reading the schematics to the Atari 2600 sometime. Tristate logic all over the bloody place. (At least, to my poor, untrained eye.) Tristate is still used, but almost always in support of digital-binary logic. I don't think there's too much interest in creating a trinary logic computer. Such a device would be more trouble than it's worth.

          As usual, Wikipedia has an article [wikipedia.org].

          • Re: (Score:2)

            by rbanffy ( 584143 )
            That's very interesting. I didn't knew the 2600 used the high-impedance state as a state in itself. Where is this used in the 2600?

          • Re: (Score:2)

            by mattr ( 78516 )
            Curious why it would be so much trouble besides difficulty in building it in 2D. There must have been some reason why Heinlein wrote (in description of the far future spaceship Dora, in The Number of the Beast) that they used trinary logic which (I think was implied) was more efficient and a math genius replied "Then you must be using triphase electrical current". For that matter, wouldn't many more than 2 states be even better, if we had some kind of optical transistor?

        • Re: (Score:2)

          by wass ( 72082 )
          You can use tri-state in modern computers

          Well, tri-state isn't really trinary per se, although outputs still have zero, one, and a high-impedance output state. The purpose of that high-impedance output is so you can stack multiple output lines (ie, multiple devices) on a bus, without them trying to overwrite each other, and you just un-tristate the relevent device through some sort of addressing.

          Despite having what appears like three output states, tristate is not trinary for a few reasons. Firstly, the c
        • You can use tri-state in modern computers (and I believe it is used) the problem comes from interference, modern microprocesser's already battle quantum effect and bulk effect, adding anouther layer make things much harder.

          As another poster mentioned, the "tri-state" used in computers isn't trinary, it's binary with a 3rd state which is "off", as in not driving any output voltage at all.

          The reason why we use binary and not trinary is because binary is simple circuit-wise -- you drive the output as hard as y

    • Re: (Score:1)

      by Phylarr ( 981216 )
      Superposition is sort of its own state in that a qubit can be taken out of superposition and put into 0 or 1 by measuring it.

      But you're right that there are an infinite number of superposition states.
    • A better way of putting it is that a Qubit has all states simultaneously. For example, both zero and one. You can talk about the probability that it will collapse to zero or one, but you can't average the probability to say that it is between 0 and 1 since there aren't any states between 0 and 1.

    • I think Wired's simplification is appropriate. My understanding of quantum computing is that a qubit can collapse to a 1, or it can collapse to a 0, or it can be in a superposition of 1 and 0. The one and zero states are pretty easy to understand--they're basically classical. It's the superposition that's the weirdo "state", and it's also the thing that makes quantum computing fundamentally different from classical computing. So, for a magazine that is trying to explain the forefront of quantum computin

    • Re: (Score:2)

      by wass ( 72082 )
      "Superposition" does not describe a single state, it just means that it's somewhere in between.

      No, a state in a superposition REALLY IS in it's own state, the Zero and One states it's a superposition of only act as a basis, but a qubit really is in a single state that happens to be a linear combination of those basis states. You can choose any two points on the Bloch Sphere to be a basis, and if you want you can even rewrite the superimposed state as being a well-defined ZERO in the newly-defined basis.

      The

  • Right what we needed (Score:5, Funny)

    by Opportunist ( 166417 ) on Monday May 07, 2007 @03:26PM (#19025705)
    The tri-state computer: Yes, no and "maybe".

    Then again, every time I use Windows, I already have the hunch that this "maybe" has already been implemented. If only in software so far.
    • I think it's more like Yes, No, Neither

    • Re: (Score:3, Interesting)

      by mandelbr0t ( 1015855 )
      Or Red, Green, and Blue.

      Or Yes, No, Cancel.

      A, B, Both.

      It's a third state. We can interpret only in context. Heck, not everything can even be expressed as having 3 states. (On, off, no power?) And many can be expressed as having more.

      Ultimately it's just another set of physics which can represent a state machine. It seems that the progress made is that a quantum 'gate' can be created. However, lacking any kind of timing mechanism (anyone know a periodic oscillater than can produce microwave radiation?), it s

      • It is much stranger than trinary values like red,green,blue.

        The implication is that all the solutions are in there and when you pick the input states everything stabilizes to the correct answer *PPOPOOF*.

        The best doc on the subject that I read is the instructions for the perl module docs for Quantum::Superpositions [cpan.org]. It is not in any way necessary to know (or even like perl) to read the pod pages for the module.

        It was fashionable in perl, for a while, to try to solve problems with superpositions. I

      • The magic happens when the bits are linked. If we use 1, 0 and B, we can evaluate an eight qubit number as BBBBBBBB, which is all of the values 0-255 at the same time. Ternary logic has no equivalent - the number '22222222' is just that - a set figure, not a multitude of values.
    • Well you know...In Soviet Russia... [wikipedia.org]

    • Re: (Score:3, Insightful)

      by $RANDOMLUSER ( 804576 )
      The Progress 4GL (and database) has a tri-valued boolean: true, false and unknown. There are times when it's useful, rather than saying "assume true" or "assume false", you can say "don't know yet".
    • enum Bool
      {
              True,
              False,
              FileNotFound
      }; :)

      http://worsethanfailure.com/Articles/What_Is_Truth _0x3f_.aspx [worsethanfailure.com]
    • Or, True, False, FileNotFound [worsethanfailure.com]
    • Funny...but...Back in the early days of computing, the Soviets were experimenting with a "tri-state" computer. IIRC it used zero and 2 different voltage settings on the "flip flop" circuit. I am talking REAL early days here. The tale was that the Russians stole an entire OS/360 model 30 mainframe from a Berlin bank and based their later computer systems on that tech dropping the earlier work.
    • True, False, and File Not Found. [worsethanfailure.com]

      -the hermit

  • Made Progress? (Score:5, Funny)

    by MarkLewis ( 593646 ) on Monday May 07, 2007 @03:26PM (#19025723)
    There are two possible end states: the researchers made progress or not.

    But until you actually make an observation by clicking on the link and reading the article, the outcome will still be indeterminate.

  • Listen up everybody! (Score:5, Funny)

    by Doctor Memory ( 6336 ) on Monday May 07, 2007 @03:27PM (#19025731)
    Slashdot's got an article that says "Timogen writes to tell us Wired is reporting that a research team is reporting that"...

  • Interesting (Score:2, Insightful)

    by nlitement ( 1098451 )
    It feels as if we were recreating computing, making the first steps again that were made during the 1920s-1940s in computing.

    • Re: (Score:1)

      by deviceb ( 958415 )
      The same seems true for me. Will we need to rewrite all software to really be able to use the power? i hope quantum pcs are out before im dead.
  • I love the idea of quantum computing but I'm tired of seeing articles that say "Progress has been made in QC" or "Breakthrough in QC". Why don't we have a checklist available so that we can cross something out on the checklist every time progress is made. This way we can see exactly how much closer we are to getting QC to the market.

    • Re: (Score:3, Funny)

      by jddj ( 1085169 )
      Why don't we have a checklist available so that we can cross something out on the checklist every time progress is made.
      • Features Quantum Entanglement - Yes and No.
      • Scalable? - Yes and No.
      • Low Power? - Yes and No.
      • Will it run Linux? - Yes and No.
      • Beowulf Cluster? - Yes and No.
      • DRM-Free? - Yes and No.

      ...I could go on all day...

      • Re: (Score:2)

        by thewils ( 463314 )

        Features Quantum Entanglement - Yes and No.

        You mean: Features Quantum Entanglement - Yes, No and Maybe.
    • Actually there is one list of criteria that is widely accepted in the quantum computing research community.

      David DiVincenzo, of IBM, listed the following requirements for a practical quantum computer:
      - scalable physically to increase the number of qubits
      - qubits can be initialized to arbitrary values
      - quantum gates faster than decoherence time
      - Turing-complete gate set
      - qubits can be read easily

      This is from wikipedia's quantum computer [wikipedia.org] entry.

      Unfortunately the article itself does not use that list, so their progress is hard to judge...

    • Here you go!

      1. Propose a quantum computer
      2. ???
      3. ???
      4. ???
      5. ???
      6. ???
      7. (etc) ...
      n. Profit!

      I think we're up to 3.

  • Dr. Tsai says the NEC group is working on a more complex, five-step procedure that will allow some basic logic to be carried out. He hopes it will be completed by the end of the year.

    .

    My understanding was that for example, if you had an encrypted file, quantum computers could decrypt it by passing all possible keys at the same time, giving you the "answer" (0 or 1) near instantaneously. If the researchers have just "one" logic gate, isn't that enough to solve the decryption problem?

    • Quantum decryption (Score:5, Informative)

      by wurp ( 51446 ) on Monday May 07, 2007 @04:17PM (#19026615) Homepage
      Quantum computers don't turn NP into P. I.e. they don't let you solve NP problems (where recognizing a correct answer is very easy but you have to test all answers to see which is correct) in an amount of time that is a polynomial function of the size of the input.

      There are two specific algorithms for quantum computers that have a big impact on encryption:

      Shor's algorithm [wikipedia.org] lets a quantum computer factor a number in polynomial time. It requires a number of qubits that is some multiple (greater than 1) of the number of bits in the number. So, once we have quantum computers with a few thousand qubits, all encryption mechanisms based on the difficulty of factoring numbers (which is most mechanisms) are broken.

      Grover's algorithm [wikipedia.org] lets a quantum computer look up an entry in an unordered dictionary in N^.5 time, where N is the number of entries in the dictionary.

      Grover's algorithm, if I understand it properly, is a Big Deal. When they say "look up an entry in a dictionary", they really mean "give an entry for which an arbitrary algorithm returns a desired value". Essentially, it means you can solve any NP problem in N^.5 time. For example, with a simulation algorithm you could find a satisfactory design out of 100,000,000,000,000 different computer designs in 10,000,000 applications of the simulation algorithm, as opposed to the 100,000,000,000,000 applications it could take on a normal computer.

      Another example of applying Grover's algorithm would be cracking a password (regardless of the encryption algorithm used). Let N be the number of possible password combinations. On average cracking a password would take N/2 applications of the encryption algorithm using a normal computer; it would take N^.5 applications using a quantum computer.

      Quantum computing doesn't invalidate encryption, but real QC would essentially invalidate encryption algorithms based on the difficulty of factoring large numbers and substantially reduce the difficulty to crack any other algorithmic encryption.

      Of course, one time pads are still totally unbreakable if used properly...

      • Re: (Score:1, Informative)

        by Anonymous Coward

        Essentially, it means you can solve any NP problem in N^.5 time.

        Not quite. Grover's algorithm will give you a quadratic speed up in searching problems. This means if a search can be completed in O(f(n)) time then with Grover's algorithm it can be completed in O(f(n)^.5) time. If f(n) is superpolynomial, then f(n)^.5 will also be superpolynomial, so this won't let you calculate anything polynomial time that wasn't already calculable in polynomial time.

        Grover's algorithm is still a huge deal though. It can be

        • Re: (Score:3, Informative)

          by wurp ( 51446 )

          Essentially, it means you can solve any NP problem in N^.5 time.

          Yeah, crap, I shouldn't have said that. I think the rest of the post is on target, though...

          I wasn't trying to claim that Grover's algorithm would let you solve problems in polynomial time. I may well have expressed the time taken incorrectly... hmm, it seems to me that saying "it takes N^.5 applications of the algorithm versus N applications for a classical computer" is equivalent (in terms of the speed) to what you said.

          I do think that qual

          • Re: (Score:3, Informative)

            by wurp ( 51446 )
            OK, double crap, I think what I said was mostly OK.

            Remember, here the N I'm talking about is the number of possibilities, not the amount of data it takes to represent those possibilities. So for 16 million possibilities the N I'm talking about is 16 million, not 24 (the number of bits it takes to represent 16 million possibilities, and the typical usage of N in the O(N) notation).

            Of course, you're right that my comment there didn't include the time it takes for f(x) to execute, but for many applications th
      • In terms of private-key encryption, it's very easy to counter the improvement given by Grover's algorithm - just use double sized keys. Instead of using AES-128, use AES-256... This is because sqrt (2^256) = 2^128.

        • Re: (Score:2)

          by wurp ( 51446 )
          Sure, but the problem is that as far as I know all private key encryption currently in wide use is based on factoring large numbers. Which means Shor's algorithm applies. Which means that there's no longer that asymmetric relationship between the difficulty of encrypting data and decrypting it, which makes the encryption worthless.

          I imagine that there are well known non-factoring based private/public encryption (elliptical, etc.). We could switch to those. That doesn't help with data that's already out

  • Can someone please explain this to me... (Score:5, Interesting)

    by powerpants ( 1030280 ) * on Monday May 07, 2007 @03:48PM (#19026075)
    TFA states:

    ...a qubit can have three possible states -- one, zero or a "superposition" of one and zero. This unique property theoretically makes quantum computing able to solve large-scale calculations that would dwarf today's supercomputers.
    Trying to understand this claim better, I followed wired's link to this article [wired.com], which states:

    ...in a QC, the bit is upgraded to a quantum bit, or qubit, that doesn't need to choose between 1 and 0. It can be both at once. As a result, a memory array of n qubits can represent every number between 1 and 2^n simultaneously. A QC's capacity doubles with each additional qubit. It may be humbling that the world's largest QC is currently only 7 qubits in size, and can barely process single-digit numbers. But a QC of 333 qubits would be able to perform operations instantaneously on every number between 1 and a googol (10^100), a value considerably larger than the number of atoms in the universe. To carry out addition or multiplication on every positive integer between 0 and 10^100 would take one of today's supercomputers several quadrillion years as it marched through one number at a time. But a QC would perform the calculation all at once, and it'd be done.
    I can (kinda) understand how n qubits can store every number between 1 and 2^n, and I can (very vaguely) imagine how that allows one to perform calculations on all those numbers simultaneously. Assuming all of that is true and good, what would one do with the output? For example, let's say I take sqrt(1 to 2^n) and get glurg as a result. Does glurg really hold the sqrt of all those numbers, and if so, how do I access them individually?
    • It can compute the solution instantaneously, but reading the answer will take several quadrillion years.

    • Re: (Score:3, Informative)

      by Anonymous Coward
      You can't access them individually.

      You can measure your system and observe the value sqrt(k) for some random k between 1 and 2^n. This doesn't buy you anything as it is trivial clasically to choose a random k and compute its sqrt.

      Or you can take "glurg" and apply some funky quantum gates to it and *then* measure your system and get n strange bits out of it. This can buy you something if you take a quantum computing class to learn how to design a useful quantum post-operation and analyze exactly what the out

    • Re: (Score:3, Informative)

      by locofungus ( 179280 )
      I can (kinda) understand how n qubits can store every number between 1 and 2^n, and I can (very vaguely) imagine how that allows one to perform calculations on all those numbers simultaneously. Assuming all of that is true and good, what would one do with the output? For example, let's say I take sqrt(1 to 2^n) and get glurg as a result. Does glurg really hold the sqrt of all those numbers, and if so, how do I access them individually?

      Those aren't the sorts of problem you ask to a quantum computer. Even if

      • Re: (Score:2)

        by wurp ( 51446 )
        That is not entirely true - a quantum computer can't just test all bit combinations at once and tell you which one has the property you want. See my other post [slashdot.org].

    • Re: (Score:3, Informative)

      by BlueParrot ( 965239 )
      Simply put, for SOME calculations you MIGHT be able to get ONE answer, the shiny part is that it is sometimes possible to make the computer give you the interesting answer and none of the ones you don't care about. I.e if you try to factorize a large integer you can set up a QC to calculate the result of dividing it by every other integer, and if you do things right you can make it output only those integers which yield a result of 0. I'm not completely sure, but I think this is possible for only certain pr
    • Let us say you have 64 qubits representing all possible keys. Now do the encryption and xor with known ciphertext. Now you have 64 new qubits, with a superposition of 2^64 states, only one of which is all zeroes. However when you put that together with the 64 bits representing all possible keys, you don't have a superposition of 2^28 states, only of 2^64 states, since each state in the result corresponds to exactly on "key state".

      Now consider the 128 qubits together as a set. You have to pull out the one

    • Re:Can someone please explain this to me... (Score:4, Informative)

      by filou007 ( 911971 ) on Monday May 07, 2007 @06:04PM (#19028313)
      You can't access the results individually, and that's the catch. QC does not lead to an exponential speed-up because, even though the "model" says every computation is performed simultaneously, you can only access ONE of the result. As soon as you read one result all the others "collapse" to that result. Imagine a 256 pages book containing the square root of the first 256 integers. Then the only thing you can do is randomly open the book to any page. Say you get sqrt(4)=2. Then every other page of the book holds a 2. You can still use QC to an advantage, but you have to be tricky: waiting as long as possible to read the output and making "interference" operations to increase the probability of the desired answer to show up. That is how a QC can theoretically search an unsorted array in a time proportional to SQRT(n).
  • Unforgivable!

    - Mensa Grammar Police
  • I tried to read the article, but my qubits started aching and my quantum bits started acting up. Somebody summarize me whats going on in this article please.
  • As you know, quantum computers require a recoding of applications to take advantage of the qubits.
    As an example, our research group has beeen working feverishly on porting Q-Bert [yimg.com] to Qubits.
  • When these texts compare bits to qubits, they use to say that the former has two possible values (1 and 0) while the later has an additional superposition state. This makes sense when you consider the bit as pure information. But AFAIK then we're comparing apples to oranges, since qubits are physical entities, while bits are logical ones. IMHO, a more correct comparison would be between qubits and electrical gates, which are bits' physical counterparts. And, guess what? Gates actually have 3 states too (0,

    • Maybe I'm wrong in doing this, but at least it makes the whole subject a little more intuitive for me.

      You're wrong in doing that, but you're also wrong in assuming that it can be made intuitive. It just isn't, in much the same way that if you think quantum mechanics is intuitive, you probably don't understand it. Nothing personal; this stuff really is that complex.

  • Couldn't you actually summarize what is new in this development instead of going on and on about qubits?

    So let me try to quote the relevant bits (hehe) from the article:

    Until late last year, if you had qubit A and you needed it to be coupled to qubit B in order change the state of qubit B, you'd have to keep that link constantly active. This link -- the coupling -- is made possible by quantum entanglement. But keeping the link active is a problem because it will also change the state of qubit A -- when y

  • First, the team took a qubit A in superposition and a qubit B in either state zero or one. Next, they coupled the two qubits using a microwave focused on a third qubit, which entangled the other two. Nearly instantaneously, both qubits would be in superposition and the coupling would be turned off. Finally, the superposition for qubit A would remain -- preserving its initial quantum state. I have been staring at this for quite a while wihtout quite getting it. Did the superposition of A get transferred to
  • I need Ted Stevens to provide me with a simple explanation of how this works!
    • The quantum computer is a big truck driving around in a series of tubes. I had an Internet on order to be delivered to my quantum computer next Friday, but I got it yesterday.

  • But What Direction? (Score:3, Funny)

    by Flwyd ( 607088 ) on Monday May 07, 2007 @06:01PM (#19028279) Homepage
    The more progress we know the researchers made the less we can know about how close they are to a solution.
  • Here's where they're at... they know exactly how close they are to success. They just don't know how fast they're getting there.
  • "Wired" is reporting that the journal "Nature" is reporting on this. Why do we insist on going through middle men?

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