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Supercomputing Science Hardware

Team Constructs Silicon 2-qubit Gate, Enabling Construction of Quantum Computers (phys.org) 92

monkeyzoo writes: A team at the University of New South Wales (UNSW) in Sydney has made a crucial advance in quantum computing. Their advance, appearing in the journal Nature (abstract), demonstrated a two-qubit logic gate — the central building block of a quantum computer — and, significantly, did it in silicon. This makes the building of a quantum computer much more feasible, since it is based on the same manufacturing technology as today's computer industry. Until now, it had not been possible to make two quantum bits 'talk' to each other — and thereby create a logic gate — using silicon. But the UNSW team — working with Professor Kohei M. Itoh of Japan's Keio University — has done just that for the first time. The result means that all of the physical building blocks for a silicon-based quantum computer have now been successfully constructed, allowing engineers to finally begin the task of designing and building a functioning quantum computer.
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Team Constructs Silicon 2-qubit Gate, Enabling Construction of Quantum Computers

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  • by Anonymous Coward

    We done got fucked out of good publicly available encryption for decades at least. The beast won. Resistance is futile.

    • Re: (Score:3, Interesting)

      by monkeyzoo ( 3985097 )

      Say goodbye to asymmetric encryption.
      Symmetric like AES can still survive quantum attacks with a doubling of key length. But all the current asymmetric algorithms are in peril once quantum computers exist.

      • by Junta ( 36770 ) on Tuesday October 06, 2015 @01:48PM (#50672513)

        Of course the issue being that AES isn't useful in many contexts without key exchange, which is generally rooted in asymmetric algorithms. Pre-shared key circumstances exist, but are exceptionally rare and not particularly feasible in most internet contexts.

        Such a strategy using username/password as foundation of the strategy can work once a relationship is boot strapped, but no good way to bootstrap a new secure relationship.

      • by Bob the Super Hamste ( 1152367 ) on Tuesday October 06, 2015 @01:50PM (#50672527) Homepage
        Well AES, Twofish, serpent, etc. were all designed with quantum computers in mind hence the 256 bit key lengths. To brute force with even with quantum computers it takes more energy than can be reasonably harvested from our sun [schneier.com]. What I wonder is if there are other weaknesses in symmetric key crypto that can be exploited with quantum computers that aren't a brute force attack. This is where the interesting results will happen.
        • I may misunderstand this -- my quantum physics are hazy at best -- but I am under the impression that "brute force" isn't the leverage that quantum computing will apply to the problem.

          Can anyone who actually understands what a quantum computer could do give us (ok, me) a lesson on the nature of the threat to encryption?

          • As others have mentioned both Grover's and Shor's algorithms which do better than regular brute force when applied to the correct type of cryptography. For symmetric key crypto it makes the problem substantially easier as in it effectively halves the key length. Even effectively halving the key length would require brute forcing the rest of the work, assuming the algorithm isn't broken in other ways. For asymmetric key crypto like RSA it is broken as prime factorization is trivial using quantum computers.
      • by slew ( 2918 )

        Say goodbye to asymmetric encryption.
        Symmetric like AES can still survive quantum attacks with a doubling of key length. But all the current asymmetric algorithms are in peril once quantum computers exist.

        Say hello to quantum encryption to replace some uses of asymmetric algorithms (which are often only used to exchange keys for symmetric algorithms).

        The real danger is to public-private key signature algorithms (such as those used to sign certificates). At some point these may need to change to use proof-of-work (e.g., bitcoin) style authentication or other cost prohibitive measures...

        • Say hello to quantum encryption to replace some uses of asymmetric algorithms (which are often only used to exchange keys for symmetric algorithms).

          Quantum computers will only be available to those that can afford them so at first you'll see yet another huge capability imbalance between the haves and the have nots. If quantum computer does eventually become cheap enough for the average consumer, I'm not sanguine it will occur in my lifetime.

        • by TechyImmigrant ( 175943 ) on Tuesday October 06, 2015 @03:42PM (#50673705) Homepage Journal

          Say goodbye to asymmetric encryption.
          Symmetric like AES can still survive quantum attacks with a doubling of key length. But all the current asymmetric algorithms are in peril once quantum computers exist.

          Say hello to quantum encryption to replace some uses of asymmetric algorithms (which are often only used to exchange keys for symmetric algorithms).

          The real danger is to public-private key signature algorithms (such as those used to sign certificates). At some point these may need to change to use proof-of-work (e.g., bitcoin) style authentication or other cost prohibitive measures...

          No, there are quantum secure public key algorithms. They are around 2X less efficient on key size than ECC. So it's not a huge problem.

        • Quantum encryption? How does that work? "The message changed when I read it!"

      • SSI ECDG signing is immune to QC:
        https://en.wikipedia.org/wiki/... [wikipedia.org]
        +
        https://en.wikipedia.org/wiki/... [wikipedia.org]

        Also, NTru encryption is immune to QC.
      • Say goodbye to asymmetric encryption.
        Symmetric like AES can still survive quantum attacks with a doubling of key length. But all the current asymmetric algorithms are in peril once quantum computers exist.

        The selling point of things like lattice crypto (e.g. NTRU) is that it is quantum attack secure.

        But don't worry. They aren't going to build a working quantum computer that can factor large numbers or solve the DLP over elliptic curves. They can't make things that cold.

      • No more locked bootloaders like Secure Boot or iBoot.

      • by delt0r ( 999393 )
        Err just no. First of all there is a lot more to running the factoring method on a quantum computer than getting enough qubits (right now you need more than 1000). You need to keep it coherent for the many many operations that have to be run on it. Also building a QC is exponentially difficult. It is not like "just add a qubit" adding a single qubit to make 3 qubits is on the order of 2x harder than 2 qubits. Going from 100 to 101 qubits is again 2x harder than the 100 qubits. You get the idea.

        So even if
    • by eexaa ( 1252378 )
      • by Junta ( 36770 )

        The challenge being that the dust is far from settled on the quantum-resistant asymmetric hashes, and none of them have been anywhere near as well researched as RSA or even elliptic curve.

        I can't reasonably today set up a website certificate using any quantum resistant algorithm. More research and consensus are required. It may be pessimistic to say no meaningful encryption for decades (it ignores symmetric encryption, this step actually isn't *practically* any closer to producing the theoretical quantum

  • by lgw ( 121541 ) on Tuesday October 06, 2015 @01:32PM (#50672379) Journal

    This step forward makes "quantum computing" real to me. Up till now, it's all been so experimental that it was divorced from engineering, and for me the target of much skepticism. Now that it's being done in silicon, however, it's on its way to being a product. Finally we might get past the hype and see what can actually be delivered!

    • by KGIII ( 973947 )

      I want to know if it can solve the N Problem. *nods* Or, really, if it can be used to play Crisys.

    • by creimer ( 824291 )

      Finally we might get past the hype and see what can actually be delivered!

      Whether the cat is alive, dead or both?

    • Re: (Score:2, Interesting)

      by Anonymous Coward

      From the article, I understand that they have managed to entangle 2 particles together in a silicon chip. In a true quantum computer, you want to have much more than 2 particles entangled together. Adding many of those 2-particle-entangled chips isn't going to create a bigger quantum computer.

      The hard problem with quantum computers is decoherence. Maintaining 2 particles entangled is easy but maintaining 10 is very hard because the particles naturally tend to "collapse" as soon as they interact with anythin

      • Measurement, collapse and entanglement are the same thing : https://www.youtube.com/watch?... [youtube.com]

        • by Anonymous Coward

          Yes. In a quantum computation, you want to set your qubits in an initial entangled state and let the computation "run". At the end of the computation, you will read the qubits, thus collapsing the state of your qubits (measure or collapse, same thing).

          Now what is very very important is that while the computation is running, the qubits need to stay entangled. If a photon (or anything else for that matter) passes through your qubit gate and collapses the entanglement, you will not read any useful results out

  • So we can try and factor 0,1,2 and 3?

    • by Anonymous Coward

      in case you need 0,1,2 or 3 factored really, reaaly fast.

      Science, huh?

  • Translation ... (Score:5, Interesting)

    by DrJimbo ( 594231 ) on Tuesday October 06, 2015 @01:53PM (#50672561)

    The real problem with quantum computers is noise and decoherence. To make a practical quantum computer you need three things:

    1) Qubits thare are very loosely coupled with the environment so they have a long decoherence time
    2) A way of coupling these qubits to each other without destroying (1).
    3) A way of reading from and writing to qubits without destroying (1) or (2).

    I *think* this paper claims to have solved (2) and (3). I believe (1) had previously been solved by the use of electron spin with atoms of Silicon-28 which this paper uses as well. Do a search for "qubit silicon 28". I think a saw a measured decoherence time of 200 microseconds. This would mean that a calcuation would need to be completed in well under this time in order to not get swamped out by noise from the environment.

    • by Anonymous Coward on Tuesday October 06, 2015 @02:10PM (#50672699)

      So if all these problems are solved why are they wasting their time publishing a paper instead of taking over the world?

      • by DrJimbo ( 594231 )

        From the fine article:

        Dzurak noted that that the team had recently "patented a design for a full-scale quantum computer chip that would allow for millions of our qubits, all doing the types of calculations that we've just experimentally demonstrated."

        He said that a key next step for the project is to identify the right industry partners to work with to manufacture the full-scale quantum processor chip.

        ISTM that if you want to find the right industry partners and avoid a lot of "it can't be done" BS, there are worse ways than first publishing a paper in a prestigious journal.

    • So... does this mean I learned binary for nothing?
      • by DrJimbo ( 594231 )

        So... does this mean I learned binary for nothing?

        Sometimes it does mean that and sometimes it doesn't mean that.

        • So... does this mean I learned binary for nothing?

          Sometimes it does mean that and sometimes it doesn't mean that.

          Are you Shor?

          • by DrJimbo ( 594231 )

            So... does this mean I learned binary for nothing?

            Sometimes it does mean that and sometimes it doesn't mean that.

            Are you Shor?

            There are several factors to consider, but just like Schroedinger's cation, I'm positive!

      • by ichthus ( 72442 )
        01001110 01101111
    • by esonik ( 222874 )

      The authors report coherence times of 120us and 61us for the two (slightly different) Qubits. Experimental evidence for Qubit Q2 is provided in the Supplementary Material and for Qubit Q1 in reference 4.

      Also, citing:
      " the error can be less than 1%, corresponding to a fidelity above 99% for the two-qubit CZ gate. The fast two-qubit operation frequency implies also that over 100,000 CZ gates can be performed within the single-qubit coherence time. [4]"

      and further

      "The tremendeous progress of quantum erro

  • by rickb928 ( 945187 ) on Tuesday October 06, 2015 @01:57PM (#50672611) Homepage Journal

    How much closer they are to a Beowulf cluster of these...

    • by myrdos2 ( 989497 )

      Wow. I just had a Pavlovian response to say something about Natalie Portman. I.. I think I need to go lie down now.

  • Quantum Computers already exist...
    http://www.dwavesys.com/d-wave-two-system

    Perhaps TFA could be more specific on what aspect this changes.

    • D-Wave's claimed quantum computers depend very much on what you call a quantum computer. D-Waves machines use a form of quantum annealing https://en.wikipedia.org/wiki/Quantum_annealing [wikipedia.org] but they are not a universal quantum computer in the traditional sense, and even for quantum annealing they are very limited in what they can do and it isn't even clear that the problems that the D-Wave machine can do are any problems where we should expect any actual speedup from a quantum computer, and certainly the D-Wav
  • by Anonymous Coward on Tuesday October 06, 2015 @09:39PM (#50676249)

    Hi everyone,

    If you don't have a subscription to Nature, you download a copy of the preprint from arxiv.org at this link.

    http://arxiv.org/pdf/1411.5760.pdf

    Enjoy! This is great Science. Even without the really cool Quantum effects, this technology has potentially far higher logic densities than CMOS.

  • Imagine a Beowulf cluster of these! Sorry, been wanting to say that for years ...
  • Sorry, but every time I dig into this, it seems to reduce to a complicated version of trying to get something out of a balanced system which won't budge due to the Laws of Reality.

    If you could just get one of those fridge magnets to turn off for half the engine cycle, you could build a truly awesome car! But fridge magnets don't give free lunches.

    Similarly, if try to pull a measurement out of your q-bit, it stops being in super position and just becomes another dumb binary switch.

    Solving a problem is

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