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Technology Science

German Scientists Create 5 qubit Quantum Register 206

Posted by timothy from the sehr-klein dept.
CMan0 writes "In the University of Bonn, a team of scientists has built a 5 qubit register, using cesium atoms trapped by a laser-beam grid, The Register reports. They've been able to install an empty 5 bit register(i.e. all bits 0), change two of them to 1, and later read those 1s back. The next goal is to create an interaction between 2 bits. The full scientific article can be found here in PDF format."
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German Scientists Create 5 qubit Quantum Register More

German Scientists Create 5 qubit Quantum Register

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  • "What's a qubit?", (Score:4, Funny)

    by Anonymous Coward on Tuesday October 12, 2004 @07:31AM (#10502232)
    Noah inquired.
    • Actually, that was Bill Cosby - or at least it was part of the act he did at the first Gator Growl he headlined (not hte one in 2002)...

    • Re:"What's a qubit?", (Score:5, Informative)

      by maxwell demon ( 590494 ) on Tuesday October 12, 2004 @08:08AM (#10502485) Journal
      A qubit (for "quantum bit") is the basic information unit for a quantum computer (just as the classical bit is for classical computers). They are actually two-state quantum systems (just as ... Ok, I'm repeating myself :-))

      The point is that quantum systems have properties which are not found in classical systems. For one, they cannot be just in the states "0" or "1" (in the usual notation for quantum states: |0> or |1>), but also in so called superpositions of those states. Such a superposition means that they are something like both states at the same time (remember Schrödinger's cat? That's exactly such a state, except that unlike atoms, cats cannot actually be brought into such a state). More importantly, such a superposition can extend over more than one qubit, in which case each single qubit doesn't have a defined quantum state at all, but only the whole set of qubit has. This is called entanglement.

      Now, why is this so useful? Well, assume you create a set of, say, 8 qubits which are all "half zero, half one". And now you perform a normal calculation on them (but with quantum operations). Then you are actually performing the calculation on all 8-bit combinations, at the same time, i.e. for all numbers between 0 and 255. This remarkable effect is called quantum parallelism.

      Now, of course there's a catch: You cannot read out more than one of the results (because reading out one destroys the superposition), and which one you get is essentially random. Ok, you now may think, I can effectively make the calculation just for one randomly selected number? So this is actually a disadvantage? Well, the point is that you can not just do "classical" calculations, but you can add operations which are not possible in classical computers. For example, there are several "half zero and half one" bit states, and you can do a quantum operation to convert one of them to |0> and one of them to |1>. Therefore you can extract properties of that result which depend not on just one of the results, but on several of them. And this allows you to actually reduce the numeric complexity of certain tasks. For example, you can search an unsorted database in O(sqrt(N)) time, instead of the classical O(N) time (N being the size of the database). The most famous algorithm is of course Shor's algorithm which allows factorizing large numbers in polynomial time, thus allowing to break public key encryption systems like PGP.

      Now, there's not too much danger yet, since AFAIK the biggest number successfully factorized with a quantum computer is 15. But then, as long as 5 qubits are newsworthy, you cannot expect too much (imagine a message that someone managed to build a classical 5-bit computer!).

      • Re:"What's a qubit?", (Score:5, Informative)

        by JohnFluxx ( 413620 ) on Tuesday October 12, 2004 @08:59AM (#10502872)
        Just to expand on this post, you can treat |0> and |1> as vectors. Well actually they are vectors.

        So |0> is [1,0] and |1> is [0,1]

        So a "superposition" is simply A*|0> + B*|1>
        = [A,B]

        Nothing particulary fancy or anything.

        The analogy I used to explain it to my dad is this:

        Imagine I have a light bulb, with a dimmer switch. I could set this to a dimmer switch to anything in between on and off. Theoritically I could store an infinite amount of information in the dimmer switch. Imagine I took a large book, converted it to hex, and turned that into one long number. Then I prepended 0. to the front.

        So you get "0.1939434....". Then I set the dimmer switch to that exact value.

        But, if I want to look at the light, for some reason, I can only see if it's on or off. The chance I see it as being on is the same as the dimmer switch setting. (So if it's set to 0.5, then I have a 0.5 chance of seeing it as on, and 0.5 chance of seeing it's off).
        I'm stretching this analogy a bit, but you can see that despite storing anything I want, I can still only read it as on or off.

        So.. how do we use this usefully? We don't really know many practical uses, but what you can do is do calculations.
        Say you put two of these lights in a room. Both are set to 0.5 brightness. With the case of the lights, the total brightness is now 1. So we've gone from having probability, to something definite. You are always going to see that as being on.

        The analogy doesn't quite fit, but you can see how you can use the underlying probability to do calculations and get a definite answer.

        • Re:"What's a qubit?", (Score:2, Informative)

          by slimak ( 593319 )
          With the case of the lights, the total brightness is now 1. So we've gone from having probability, to something definite. You are always going to see that as being on.

          Maybe I don't understand the analogy...

          Assuming that the light uses a dimmer switch as described in http://home.howstuffworks.com/dimmer-switch.htm/p r intable [howstuffworks.com] then the two lights will both be on/off at the same time (same sinusioudal source begin converted to on/off signal). So, the probably of light being on is still 1/2.

          If instead, w

          • I was kinda hoping you didn't know that a dimmer switch doesn't make the light dimmer, but rather turns it on and off rapidly.

            I was thinking along the lines of using a variable resistor, like you say.
            The intensity would then be at X/2 for each light. Then when you put both lights in the same room, the total would be X. (Where X is the full brightness for a given light).

            I agree with what you say though. It's hard to come up with perfect analogies.

    • Analysis & request for help (Score:5, Interesting)

      by tbo ( 35008 ) on Tuesday October 12, 2004 @02:08PM (#10505980) Journal
      Disclaimer: I'm a graduate student doing research on quantum computing in optical lattices. I'm not affiliated with the group that published this article.

      This result is quite exciting, because it demonstrates the feasibility of some of the techniques necessary for an optical lattice-based quantum computer. Imagine taking their 1-D lattice and turning it into a 3-D lattice, with about 30 atoms in each direction. That's a whole lot of qubits...

      So what are the next steps?
      1) A new means of addressing atoms (selecting one or two atoms on which to perform operations while excluding the rest) is necessary. Their magnetic gradient technique works fine for a small 1-D lattice, but it would likely be impractical for a large 3-D lattice (Maxwell's equation div B = 0 gives one major obstacle, which would require fancy tricks to overcome).
      2) One and two-qubit gates need to be demonstrated using an appropriate addressing scheme.
      3) Error correction, which would likely require quantum non-demolition measurements to check to see if an atom had been lost from a lattice site. Translation: we need to be able to measure if we've lost an atom from a lattice site, without disturbing the atom's state (i.e. measuring whether it's |0> or |1>).
      4) Full-blown fault-tolerant computation.

      My group plans to solve (1) using an addressable optical lattice. What that means is that the lattice spacing is sufficiently large that a laser can be focused on an individual atom (in 3-D, two lasers in orthogonal directions would be used). I'm currently doing simulations of one-qubit gates in this scheme.

      That brings me to my question for slashdot: Some of the simulations I'll be doing (specifically, studying decoherence in the one and two qubit gates) will be very computationally intensive. They're also embarrassingly parallel, as they're essentially quantum Monte Carlo simulations. Would people be interested in a BOINC [berkeley.edu]-based distributed computing project (a la SETI@home) to help develop quantum computers? If so, what kinds of things would help you get involved? Would you be interested in helping develop the software (it's C++)?

      I probably won't be at that stage for another six months to a year, but it would be helpful to me to start planning now. I have just (last night) completed the core simulation engine, and would need to add code for decoherence, as well as adapt it to BOINC. The code will be GPL'd, of course.

  • First quantum OS (Score:4, Funny)

    by Chuns ( 723979 ) <craig77atwork.hotmail@com> on Tuesday October 12, 2004 @07:31AM (#10502239) Homepage
    Should the first quantum OS be M$ or Linux? :) I like to watch people argue about OS's. Makes me smile.

    • Re:First quantum OS (Score:5, Funny)

      by fstrauss ( 78250 ) on Tuesday October 12, 2004 @07:33AM (#10502255) Homepage
      It'll be both until you boot it.

      • Re:First quantum OS (Score:5, Funny)

        by cyfer2000 ( 548592 ) on Tuesday October 12, 2004 @08:38AM (#10502701) Journal
        Are we still going to use mouse? Or a cat with two buttons labeled as "alive" and "dead"?
      • So dual booting won't be such a pain in the ass, then. Excellent!

        • Re:First quantum OS (Score:4, Funny)

          by maxwell demon ( 590494 ) on Tuesday October 12, 2004 @09:13AM (#10503001) Journal
          Except that you can't control which operating system comes up: That will be completely random. If you are unlucky, you'll get the desired operating system only after a lot of boot cycles.
          • Except that you can't control which operating system comes up: That will be completely random. If you are unlucky, you'll get the desired operating system only after a lot of boot cycles.

            But since all possible boot cycles happen simultaneously, this shouldn't be a problem.

            • But since all possible boot cycles happen simultaneously, this shouldn't be a problem.
              At least, until you observe it; at which point, it collapses down to a single boot cycle :)

          • Re:First quantum OS (Score:4, Informative)

            by pclminion ( 145572 ) on Tuesday October 12, 2004 @10:38AM (#10503703)
            Except that you can't control which operating system comes up: That will be completely random.

            That isn't even true with real quantum particles. You can manipulate force fields in order to skew the quantum wavefunctions, making it more likely for the outcome to be one option than another.

            Yes, the behavior is random in the purest mathematical sense, but just because something is random doesn't mean it's unpredictable or uncontrollable.

            Suppose I had a 12-sided die, which had the number 1 on each face except for a single face, which had the number 2 on it. Clearly, the outcome of the die toss is still randomly determined, even though the number 2 is only 1/11th as likely as the number 1. If I were betting on such a die, I would certainly bet on 1.

            Manipulating the potential to change the quantum wavefunction is sort of analogous to changing the shape of the die. If I squash the die so that one axis is longer than the other, and the "2" face happens to fall on the end of the long axis, then I have dramatically reduced the probability of the die ever coming up 2. (Try tossing a book in the air and see how many times it lands perfectly on its spine. Possible, but very, very unlikely.) It could happen, but perhaps only one in a million times.

    • You havn't heard? The OS comes in a box with only a picture of a cat on it, and you won't know what OS you have until you open the box and install the software. But if you actully figure out what OS you're using it'll change for absolutely no reason.

  • And God said.... (Score:5, Funny)

    by GillBates0 ( 664202 ) on Tuesday October 12, 2004 @07:32AM (#10502244) Homepage Journal
    Let there be light, and there was "1".

    • Re:And God said.... (Score:5, Interesting)

      by metlin ( 258108 ) * on Tuesday October 12, 2004 @07:39AM (#10502292) Journal
      Actually, there was uncertainty.

      Upon further observation, it was known to have a probability of 1 ;)

      On a serious note, this is awesome. With a 5 qubit entanglement and this, we might be able to build a primitive functional Quantum Computer, for the first time.

      The team is now working to create a quantum gate in which two or more qubits of the register will interact in a controlled way.

      Amazing. The beginnings of a first QC. We've memory, redundancy, processing capabilities and a lot more.

      Now the only problem that remains is a suitable and reliable means of error correction - which is the biggest problem thus far in QC :-(
      • On a serious note, this is awesome. With a 5 qubit entanglement and this, we might be able to build a primitive functional Quantum Computer, for the first time.

        I'm pretty sure that a "primitive functional Quantum Computer" has already been built. I recall IBM announcing that they had factored a seven bit number [ibm.com] using QC techniques.

        This seems promising because it's more likely to be scalable to higher numbers of bits than IBMs approach, from what I can tell.

        • Re:And God said.... (Score:3, Informative)

          by metlin ( 258108 ) *
          Well, I meant in a classical sense.

          IBM's factoring operation was a very specific deed - it's not really a quantum computer as much as a customized quantum operation for a very specific task.

          I meant something where you give an input, process it, store it and retrieve it -- entirely using quantum operations.

          That is a challenging.

          And IBM's task and this are two entirely different things, in terms of what they mean and what they've accomplished.
      • So, we're what 10 - 20 years away from a QC that both gives you your answer and blue screens at the same time?

        I started a book on QC and it's a mind-shredding topic.

        • Re:And God said.... (Score:5, Informative)

          by metlin ( 258108 ) * on Tuesday October 12, 2004 @07:57AM (#10502412) Journal
          So, we're what 10 - 20 years away from a QC that both gives you your answer and blue screens at the same time?

          Atleast.

          I would say maybe 50. It's not enough if you can get a system to do something - you need to make it reliable and scaleable.

          We're still tackling the very basic problems in QC, and have a very very long way to go. Error correction is still a very big problem.

          Some people, such as Alexei Kitaev [caltech.edu], have done some pioneering work but it's still in its infancy. A long long way to go.

          • It's not enough if you can get a system to do something - you need to make it reliable and scaleable.

            Or at least make sure it's fitted out with lots of blue LED's. ;-)

            Yeah, You're absolutely right, but I wouldn't be surprised if we are underestimating the rate of progress. On the other hand, we've been 50 years away from affordable fusion power for 50 years.

            • Actually, we have affordable fusion power since millions of years (ok, well, we don't, because we didn't exist that long). Indeed, the entire planet is driven by fusion power (with the exception of processes driven directly or indirectly by the heat from inside the earth, like continental drift, volcanoes, and some life forms in the deep sea).

        • Re:And God said.... (Score:2, Informative)

          by psetzer ( 714543 )
          The thing that's driving us crazy is the fact that adding more qubits is what makes a quantum computer fundamentally faster. For all intents and purposes, you can view a normal computer as a multicore 1-qubit quantum computer. That is, I have a computer that can handle a 32-bit word, so it's acting like 32 1-qubit quantum computers in parallel.

          A 5-qubit quantum computer isn't really that fast. It's about 32 times faster than a comparable 5-bit computer, assuming that both can perform a similar number o

      • Now the only problem that remains is a suitable and reliable means of error correction - which is the biggest problem thus far in QC :-( The only problem? How about making practical those things they've done at great expense with huge impractical devices in a lab? How about proving that entanglement is for real and isn't just "spooky action at a distance" like Einstein originally derided it? Quantum computers are decades if not longer from reality.

        • Re:And God said.... (Score:3, Informative)

          by qcomp ( 694740 )
          How about proving that entanglement is for real and isn't just "spooky action at a distance"

          All theories that try to explain what we observe without entanglement have been disproven time and again. Bell's inequalities have been violated to 10 (or was it 50?) standard deviations and in various physical systems.
          Quantum mechanics is is probably the most tested theory around, and entanglement is an integral and unavoidable part of this theory - I dont think there is particular need to "prove that it is for r

      • Actually, there was uncertainty.

        Well, there was Fear, Uncertainty and Doubt.

        Uncertainty was finally implemented int he basic laws of matter, while Fear was reserved to animals (including humans) and Doubt was reserved for the humans alone.

        You see, the entire creation is based on FUD.
    • Let there be light, ...and there was still nothing but, hell, you could see it.
  • Let us put a bit on in a box where it can be on or off after waiting a day, would it be on or off?

  • Older News. (Score:5, Informative)

    by modifried ( 605582 ) on Tuesday October 12, 2004 @07:33AM (#10502254) Homepage
    This was covered on New Scientist and IndiaTimes a few days ago. Their articles:

    -New Scientist [newscientist.com]
    -IndiaTimes [indiatimes.com]
  • Wow...
    I was just going to look for information on Quantum Computing and I thought that I might as well refresh Slashdot too...
    • Were you really sure the article was there when you read it?
    • I have that quite often: I need to find some information for my work, and that same day slashdot has an article about it. Sometimes it is almost as if Cowboy Neal himself had a camera in my office (he is probably sharing it with Scott Adams ;-) ).

      ...hey, it makes a great excuse to read /. during work!

  • Bill gates sez: (Score:5, Funny)

    by Anonymous Coward on Tuesday October 12, 2004 @07:34AM (#10502260)
    "a 5 qubit register should be enough for anyone"
  • What is the advantage of using caesium?
  • In other words, we won't be seeing any quantum computers "quite" yet.

  • Cesium and Laser Beams (Score:5, Funny)

    by blankman ( 94269 ) <.blankman42. .at. .gmail.com.> on Tuesday October 12, 2004 @07:37AM (#10502280) Homepage
    So in ten years I'll have to wear a lead apron and protective glasses when I turn on my new computer? New fashion trend for geeks that never shut their boxes off.
    • Darwin strikes again :)

      Darwin: Serveral billion - Humanity: Zilch

    • Caesium 133 is a stable isotope of caesium, there is no need to wear a lead apron. However, caesium is explosive in cold water and toxic. So, you rather than not install your motherboard in a plexiglas or plastic case or spilling your lemonade on your laptop.
      • Well, with 5 Caesium atoms, you'll not get much of an explosion. Even with 10^13 caesium atoms (which would be about a quantum-terabyte) the explosion would probably not be noticable at all. Also, in that amount the toxicity is probably negligible either.
        • In the original post, the commenter is talking about an hypothetical computer, not about the experiment. So, how much ceasium will there be in this hypothetical computer? And, these days 1 Terabyte is nothing more than 1/1000th petabytes.

    • > I'll have to wear a lead apron and protective
      > glasses when I turn on my new computer?

      Geeks have no need to wear a lead apron, for reasons that should be obvious after a moment's reflection. And as for protective glasses, well, most of us already wear them...
    • In ten years your computer will have known you wanted to use it and booted ten minutes ago, already displaying the google search results for what you were looking for!

      Just don't open the case for a peek, or you'll literally let the cat out of the bag (or case as the case may be).
  • What they didn't know, was that (like all good sci-fi comics prior to the graphic novels of the late 80's) there was only one way to unlock the door of the secret super evil overlords of darkness... and that was a 6 qubit register!

  • Not quite there! (Score:5, Insightful)

    by bWareiWare.co.uk ( 660144 ) on Tuesday October 12, 2004 @07:48AM (#10502355) Homepage
    Whilst I am sure this is a step forward there must still be a big step between creating a 5-qubit register and a 5-qubit entangled register. With what they have created can only do the same as a five bit digital computer, with the second you could <insert you favourite quantum hyperbole here>.
  • Qubit. [wikipedia.org]

    A qubit is not to be confused with a cubit, which is an ancient measure of length.

    A qubit (quantum + bit; pronounced /kyoobit/ ) is a unit of quantum information. That information is described by state in a 2-level quantum mechanical system, whose two basic states are conventionally labeled |0> and |1>(pronounced: ket 0 and ket 1). A pure qubit state is a linear quantum superposition of those two states. This is significantly different from the state of a classical bit, which can only take the value 0 or 1.

    A qubit's most important distinction from a classical bit, however, is not the continuous nature of the state (which can be replicated by any analog quantity), but the fact that multiple qubits can exhibit quantum entanglement. Entanglement is a nonlocal property that allows a set of qubits to express superpositions of different binary strings (01010 and 11111, for example) simultaneously. Such "quantum parallelism" is one of the keys to the potential power of quantum computation.

    --------- end quote -----------

    Quantum cryptography [wikipedia.org]
    From Wikipedia, the free encyclopedia.

    Quantum cryptography currently has two aspects. The first is quantum key exchange, a method for securing communications based on quantum mechanics. The second is the conjectured effect of quantum computing on cryptanalysis, although it is currently, like quantum computing itself, only a theoretical concept.

    The basic idea in quantum key exchange is to use the "noisy" properties of light to render incoherent an image that acts to complement a secret key. This image can be represented in a number of ways, but the ability to decode that image rests upon an understanding of how it was made. No way to intercept the transmission without changing it is possible, so key information can be exchanged with great confidence it has been transmitted secretly.

    Using quantum superposition as a part of the computation, quantum computing will considerably extend the reach of cryptanalysis, making brute force key space searches much more effective -- if such computers ever become possible in actual practice.

    ----------- end quote ----------
    NOTE: Please read the actual wikipedia articles. They have TONS of hyperlinks with full explanations!

  • Uh, what I'm reading... (Score:3, Funny)

    by nativespeaker ( 797751 ) on Tuesday October 12, 2004 @08:32AM (#10502654)
    We have to recalibrate the lateral baffles, and rotate the shield harmonics! Ziggy swears you should have leaped by now!

  • Awesome. (Score:4, Funny)

    by Bill, Shooter of Bul ( 629286 ) on Tuesday October 12, 2004 @08:39AM (#10502711) Journal
    They almost have a qubyte! Think of the power!!

  • Programming... (Score:3, Funny)

    by Anonymous Coward on Tuesday October 12, 2004 @09:35AM (#10503185)
    So do you program it using QBasic?

  • QC as a PC (Score:4, Interesting)

    by like.narly ( 794832 ) on Tuesday October 12, 2004 @09:40AM (#10503224)
    Unfortuantely, the way scientists see it now, we'll probably never have a desktop quantum computer (or at least for a very long time). The problem is that the interaction takes place in an extremely controlled environment. Granted, the first analog computers were large, but that's because solid state wasn't really around yet. The "parts" of most QC's are acctually on the nanometer scale.

    For example, one qbit setup is to use a helium superfluid, which naturally bonds electrons to the surface. The bound electrons can then be controled with a combination of microwave radiation and an electric potential from wafer posts under the fluid. Each electron (qbit) sits on top of a post, which are spaced just a few nm apart. The system is still being developed, but the nice thing is once they get it to work, they can just build a large wafer holding millions of qbits.

    However, the huge problem with the above example is that it needs to run at about 50 mK, which is very close to absolute zero and requires a dilution fridge, which is a 6 foot tall cylinder. There are similar (though more complicated) limitations to the laser trapping methods.

    For a commercial unit I suppose the QC wafer, microwave source, and dilution fridge could be packaged together nicely, but it is still 6 feet tall, heavy, not well suited for a house. Even if it were possible to make one small enough, there are currently no real benefits for a home user unless they really wanted to find elements in a large array or crack PGP codes... I suppose the first computers were also only suited for a lab environment and scientists probably thought the average person would never need a computer either, so who knows what will develop in the next 50 years...

    • Re:QC as a PC (Score:2, Interesting)

      by bratboy ( 649043 )
      I think there are two points to this - the first, being that we probably never thought that there'd be an atomic clock on a chip, but time marches on [nist.gov].

      The second, and to my mind more interesting point, is that the cat is, to a certain extent, out of the bag. Especially if the basic research is being done all around the world, and made freely available. There's going to be a point in time between when house-sized (but usable) quantum computers are available to governments, and when they become ubiquitous (

  • Misleading (Score:2, Informative)

    by James Turpin ( 789479 )
    I've taken a class in quantum computing, so I know a little bit (pardon the pun) about this.

    IMNSHO, It's not really a 5-qubit register until you have interaction between the bits. That is their next step, but until then, it just doesn't count. The reason is that, other than the third "indeterminate" state that randomly returns "1" or "0" (which they also do not appear to have tested), without interaction between bits they might as well be classical bits. There is no computing advantage (other than tru

  • The Network is the Qomputer (Score:4, Interesting)

    by Doc Ruby ( 173196 ) on Tuesday October 12, 2004 @11:03AM (#10503942) Homepage Journal
    "Qomputing" (qubit computing, get it?) is pursued independently across the globe, with separate teams reporting breakthrus in different pieces of the puzzle. One team has produced quantum entanglement, using "spooky action at a distance" to offer apparently instant communication between terminals. If each of these components in its distant lab were entangled in a quantum net, we'd get a qomputer built from the start to network in parallel while computing literally in parallel. Linux's unix heritage shows the compelling momentum derived from including networking from the beginning of the platform. Qomputing is born in the age of the network: entangled networks are natural midwives and gossips for a new qomputing qommunity.
  • Wouldn't it be quicker to wander down to the NSA and borrow some time on thier 2048 bit quantum-entangled computer array?

    Just thought I'd help.
  • ...God may or may not kill a kitten.

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