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Is Quantum Computing for Real?

  1. Apr 24, 2016 #1
    This week, in Sydney, there was the announcement of not one but TWO Quantum Computing centres opening at two rival universities (UNSW and USYD). There was a feature on one of the current affairs shows here with the very charismatic guitar-playing professor of one of the centres, which has had a major funding injection by Microsoft. The other centre was opened by none other than the Prime Minister, Malcolm Turnbull. (Article is here.)

    Now I understand the very basics of quantum computing - that it is based on QBits, not binary bits, which in turn exploit the phenomena of entanglement and superposition to perform calculations that would be impossible to execute in binary systems. I understand that David Deutsch is one of the main theorists behind the field, and that he is something of a science super-star (who also happens to believe in t he Many Worlds interpretation of quantum physics, which is somehow important to his theory of quantum computing.)

    But I have also read that there is scepticism as to whether a working quantum computer can be built, because of the 'problem of de-coherence', which poses a huge technical challenge. There is a company, DWave, which Google has a stake in, which claims to have produced a working quantum computer, but others, notably a physicist called Scott Aaronson, are sceptical, saying that the output could have been produced by a common-or-garden variety super computer.

    So is the quantum computer hype? Or is it real?
     
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  3. Apr 25, 2016 #2
    Theoretically, what makes a quantum computer superior to a normal, or an analog computer?
     
  4. Apr 25, 2016 #3
    It is able to solve problems with large numbers of dimensions. It could revolutionize chemistry, since molecules are quantum systems with possibly thousands of dimensions. A quantum computer could predict what such a system could do. Nowadays chemists synthesize the molecule and then see what its properties are. Very slow.

    Non-quantum computers will never be able to do that.

    As to everyday linear if-then-else computing, quantum computers are inferior and likely to remain so.
     
  5. Apr 25, 2016 #4

    phinds

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    They can do things in cryptography at speeds vastly above what will ever be even approachable by standard computers whether they are Von Neumann architecture (normal digital computers) or modified Von Neumann architechure (such as is common is DSP chips) and that are impossible in analog computers.
     
  6. Apr 25, 2016 #5

    phinds

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    That is an excellent question and so far there is no clear-cut answer. There is a LOT of hype around them but there is also a lot of criticism and it remains to be seen whether they will fulfill their promise.

    As hornbein noted, they will never be the be-all and end-all of computers since normal Von Neumann architectures will beat them ever time on many types of problems.
     
  7. Apr 25, 2016 #6

    f95toli

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    There is no question that quantum computing is "real" in the sense that we know that it works and we can already solve (small) problems.
    However, whether or not a "general purpose" QC will ever be of practical importance is still an open question.

    However, what is somewhat more certain is that the technology for quantum simulations (which is a bit like old-time analog computers) will reach a point where it will be useful in just a few years. There are lots of problems that could be addressed using this technology, most notably in quantum chemistry and biology.
    Another class of computer is the quantum annealer which is what D-Wave sells. These computers DO work and can already solve real-world problems but can't be use for e.g. cryptography/. However, they should excel for certain (important) optimization problems although so far they all circuits are so small that they can only be used for small(ish) problem where the solution times are about the same as you would get using a purpose built signal processor. But again, we should know in a just a few years whether or not they will be of any practical importance.
     
  8. Apr 25, 2016 #7
    The computers that D-Wave produce work but it is questionable as to whether they achieve Quantum speedup. I think that is where the controversy lies. Coherence times are short and it has been shown by some that a standard computer can produce results quicker than the D-Wave machine. There is quite a bit of argument between the two camps.
     
  9. Apr 25, 2016 #8
    What programming language is used for quantum computing?
     
  10. Apr 25, 2016 #9

    phinds

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    3 seconds on Google tells me that it's special "quantum languages". Dwave has their own.
     
  11. Apr 26, 2016 #10

    Fervent Freyja

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    Probably Andrea Morello from UNSW with the guitar. I vote for him to get it first.

    :oldlove: I could watch that man talk about transistors and quantum tunneling all day -- look at those expressive, high energy hands... :oldlove:
     
  12. Apr 26, 2016 #11

    f95toli

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    There is no special "language". So far everything is very low level, so you can use whatever language you want.that can create the appropriate sequence of pulses.
    Most people will probably use Matlab or Python simply because they are the most common languages for this type of task.

    D-Wave has written their own software interface for their hardware that can then be called from another programming language. I will try to remember to ask what is actually used next time I meet someone who uses it.
     
  13. Apr 26, 2016 #12

    FactChecker

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    The current capability is certainly over-hyped, but the theoretical potential is not. If you have 500 Q-bits that can solve a problem in one step, that might solve a problem that has 2500 =~ 10150 possible outcomes in one step. No traditional computer will ever be able to solve a problem that big that unless there is some shortcut algorithm to "branch-and-bound" it. Suppose there is a problem that does not allow a "branch-and-bound" shortcut solution. No traditional computer could solve it in a billion years. I don't know if there is such a problem, but it shows the theoretical potential power of the quantum computer.

    Here is a possible example problem. It may not have any practical use. Suppose we have a function f(B), where B is a series of 500 bits. The value of f is 1 if B == B0, a particular series of 500 bits, and f is 0 otherwise. We want to maximize f. It does not give you any other information about partial matches. Then there would not be any shortcut algorithm possible, and no traditional computer could find a perfect match to B0. But, in theory, a quantum computer could.

    EDIT (CORRECTION): I realize now that the example above will not work. In order to put that function into a quantum computer, you would need to know what B0 is. If that were true, you could just read it.
     
    Last edited: Apr 26, 2016
  14. Apr 26, 2016 #13
    Dear Quotidian,

    The mathematical formalism adopted by Werner Heisenberg leaves clear that in the instant the location of the particle is made, all probabilities disappear. Strangely, since the formulation to this day, numerous discussions about the significance of this disappearance occur, maintaining that there is something misterious in it (Copenhagen interpretation). So, the problem isn't an engineering one, isn't about practical things. Quantum computers are theoretical impossibilities.
     
  15. Apr 26, 2016 #14
    There is basically DWave and everyone else. The DWave system performs a "quantum annealing" - it's basically a solution in search of a problem.

    More generally, the goal is to be able to store and manipulate "qubits". A single qubit able to be in 2 states at the same time. In some devices, it can be in more than states than that. But a collection of qubits that has been deliberately manipulated by allowing that information in them to interact can be in a large number of states. For example, using simple binary numbering, 6 bits can code for any of first 17 prime numbers. But 6 qubits can code for all of those 17 primes - as a subset of the 64 possible combinations

    Perhaps the most well-known quantum computing algorithm is "Shor's Algorithm", which factors large composite numbers - intriguing because the difficulty of such factoring is the basis for RSA encryption.

    There are certain problems that are essentially impossible with normal computers that should be possible with quantum computers. But even once perfected, they will not be suitable for all computation problems. For example, the user interface to a Quantum computer will be a normal computer.

    As far as how real they are, there have been some interesting breakthroughs recently. I would say that it is inevitable that quantum computers will be developed and prove useful within the next couple of decades - perhaps much sooner. And that is excluding the DWave device.
     
  16. Apr 26, 2016 #15

    phinds

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    That does not follow from the rest of your post. How do you arrive at that conclusion? Do you have any sources or is that just a personal opinion?
     
  17. Apr 26, 2016 #16
    Dear Phinds,

    OK, if you think so. As you know, was formulated in 1926 by Erwin Schroedinger a partial differencial equation that describes how the quantic state of a physical system changes with time. For it, in 1933, he received the Nobel Prize (together with Paul Dirac).

    It contains the factor Ψ, referred somewhat improperly as "wave function". The significance of it was not understood, until Max Born interpreted it as defining the probability of finding a particle in a determinate position of space. He received the Nobel Prize for it in 1932. The possibility can be represented by a Gauss curve, with maximum in the center and coming asymptotically to zero in the extremities. The mathematical formalism adopted leaves clear that in the instant the location of the particle is made, all probabilities disappear. Strangely, since the formulation to this day, numerous discussions about the significance of this disappearance occur, maintaining that there is something misterious in it (Copenhagen interpretation). Nevertheless, when we have a dice in hand before we throw it the possibility of each face falling upside is one to six. In the moment it falls upon the table and immobilize, to us it's clear one can no more speak of probabilities, as one of the faces was defined. Its obvious, there is nothing misterious in it, as even Einstein and Niels Bohr concurred.

    Quantum computers are imaginated to work with the innumerable possibilities that would exist before the observation was made, as if they subsisted as physical things

    It seems to me a supposed “observator's influence” is therefore nonsense.

    It's what occurs when one believes that Physics necessarily must be described by mathematical formulas, even when they are not needed, as is the case. In this love for mistery, even today is frequent the understanding that the wave function signifies that the particle is in all places at the same time, and quantum theory would make possible the creation on a computer capable of realizing simultaneously infinite mathematical operations, a thing that would be useful, for instance, in breaking cryptographed texts.

    Another common mistake that has the same origin consists in "multiple universes interpretation", that erroneously affirms the objective reality of the universal wave function, when it is a mere mathematical operation.

    That I was thinking when I wrote, I would be glad if you agree.
     
  18. Apr 26, 2016 #17

    phinds

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    I don't have the detailed knowledge to follow your logic, but I have to ask, why do you suppose that so many companies are paying a LOT of money to lots of really smart people to work on quantum computers if they are, as you say, a theoretical impossibility. That's what makes no sense to me.
     
  19. Apr 26, 2016 #18
    Dear phinds,

    I don't even imagine why so many grants are conceded, but I suppose reserchers are not really interested in Physics progress and have to pay their rent in the end of the month...
     
  20. Apr 26, 2016 #19

    phinds

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    That is EXTREMELY insulting to physicists. Do you seriously think that all those people are willing to waste their professional careers just to pay the bills? That's disgusting.

    I find it MUCH more likely that you are missing something that they are not.
     
  21. Apr 26, 2016 #20

    FactChecker

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    This is too simplified. If there are several qubits entangled, their entire arrangement has a probability distribution and the entire thing becomes determined at once. In fact, that is what gives the quantum computer its potential. A system of 500 qubits could instantly settle into one of the 2500 ~ 3*10150 possible combinations. It might give the answer to a problem that a conventional computer could never solve.. The trick is to make the quantum computer settle into a solution of a problem that we want to solve.
     
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