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Can someone more inclined elaborate a bit on this please? "As opposed to traditional computer bits, which can encode distinctly either a one or a zero, qubits

by readme 15y ago

Can someone more inclined elaborate a bit on this please? "As opposed to traditional computer bits, which can encode distinctly either a one or a zero, qubits can encode a one and a zero at the same time. This property, called superposition, along with the ability of quantum states to "tunnel" through energy barriers, will some day allow quantum computers to perform optimization calculations much faster than traditional computers." I get it, a qubit can store multiple states, but if someone could give a little more on how it does that, and why that means quantum computers will be faster someday, that'd be excellent.

Radzell 15y ago
I wrote a paper in highschool so take this with a grain of salt basically the idea is have truly parallel programming instead of having concurrent ones the ability of the qubit to solve for multiple states means they can solve for multiple problems at the same time while conventional computing seems parallel whats really happening is that calculation are switching states so fast they feel parallel. If I am wrong someone correct me.
- exit 15y ago
  did you also refrain from using punctuation in your report?
- buu700 15y ago
  Yeah, that's completely off (it would be a more apt description of the distinction between multiple cores and hyperthreading). The important characteristic of quantum computation is not that it's faster or more parallel than classical computation, but that it's a generalisation of classical computation. The same way that classical mechanics describes a subset of quantum mechanics rather than disjoint phenomena, all current classical CPUs are technically "quantum" CPUs (the best kind of quantum CPUs!). So, what does this mean? Well, for all the software we have today, and for almost everything we know how to code today, absolutely nothing; in fact, most of what we can do on classical computers will be slower simply because it will be quite some time before a quantum computer is anywhere near as well-engineered as, say, a Core i7 – especially when you take into account that the properties of quantum mechanics make this engineering not only different but also significantly more difficult. What we do get from the computational paradigm shift, however, is a broader set of operations which allow for a broader set of algorithms. Take Grover's algorithm (the one mentioned in the article): http://en.wikipedia.org/wiki/Grovers_algorithm#Algorithm_steps http://en.wikipedia.org/wiki/Grovers_algorithm#Algorithm_ste... If you understand the notation, what you'll see is a series of linear operations (quantum gates) being applied to vectors (qubits (classical bits are scalars)) in a quantum circuit. These can all be used to describe any operation which would be performed on, say, an x86 core (albeit more verbosely), but can also take advantage of quantum mechanical properties to manipulate non-classical information (which gets complicated to discuss). For the canonical example of how this can significantly change computation as we know it, see Shor's algorithm, which speeds up prime number factorisation from sub-exponential time to polynomial time, and thus could potentially break RSA encryption if we had a practical quantum computer): http://en.wikipedia.org/wiki/Shors_algorithm http://en.wikipedia.org/wiki/Shors_algorithm Aside from that, I'm sure people much smarter than I am could go on in technical depth about how, despite not really being an advancement of mythical proportions in and of itself, this new class of algorithms would be able to revolutionise areas like search, machine learning, physical/biological/chemical simulation, and so on.
betawolf33 15y ago
A rather quick answer from a not-totally-grasping person: the qubit stores all the possible resultant states of an interaction with it, and then collapses to one of those values when you measure it. So you can do processing really quick because you can do explore a buckload of possibilities at once. The physical reality of the phenomenon is hard to grasp, and I'm still not totally sure I get/buy it. See http://en.wikipedia.org/wiki/Double-slit_experiment http://en.wikipedia.org/wiki/Double-slit_experiment
- rbanffy 15y ago
  It's said one cannot understand quantum mechanics. Humans can merely get used to it.
  - trafficlight 15y ago
    I've read the Wikipedia pages on Quantum Computing and qubits a few times and all I can say is, "Yes, mmhmm, yes. I know some of these words." I wonder if computing, and other sciences, will become so advanced that fewer and fewer people will be able to comprehend the fundamentals or will there be a time when things like quantum mechanics are a high school subject?
    - rprospero 15y ago
      Basic quantum mechanics could be a high school subject. While solving the hydrogen atom might be out of their reach, some simple angular momentum operators and Clebsh-Gordan tables shouldn't be beyond the reach of a sophomore.
      - greeneggs 15y ago
        Basic quantum mechanics should be a high-school subject. The way physicists teach it currently, based on its historical development instead of on the modern understanding, is tragic. It just makes everyone repeat that nonsense quote, that nobody understands quantum physics. Teaching angular momentum and Clebsch-Gordan coefficients seems pointless. There should be a standard class on probability theory and statistics. Quantum theory should be introduced as a generalization of probability theory. This is the right foundation for the field, not some vague and basically meaningless statements like particles are both particles and waves.
mathgladiator 15y ago
imagine an 2-qubit unsigned integer being all four permutations at once, then you add 1, now you have manipulated all permutations at once. However, the trick is that you haven't done anything yet. So, we need new algebras to collapse wave functions in interesting way.
Sniffnoy 15y ago
I would say this explanation is essentially wrong. It makes it sound like the difference is that the computer is ternary rather than binary, which of course would not be a significant difference. Part of this is that the "more than one state at at time" applies to the whole computer, not individual bits, but the thing is that the whole "more than one state at a time" thing isn't it either. To see this, instead of a quantum computer, let's consider a probabilistic computer. Rather than having one state, the computer at any time has a probability distribution over states -- it can "be in multiple states at once", each with some probability. Only at the end of a computation do you "collapse" it back into a single value. Except that such a computer is equivalent to an ordinary computer equipped with a TRNG, which is not much more powerful than an ordinary computer at all. Quantum computers are often described as "trying everything at once", as if they were nondeterministic Turing machines, but they are not; perhaps, in some sense, they do try everything at once, but they cannot then automatically pick out whichever possibility worked. It only "tries everything at once" in the same sense the probabilistic computer does. The probabilistic computer can only pick out the right answer if you somehow set it up that the right answer has high probability and the wrong ones don't; it can't say "this answer is right, kill all the other possibilities now!". The quantum computer is the same way. What makes quantum computers faster is the fact that instead of probabilities, they use amplitudes. To each state -- well, what I was calling states above, really they would be "basis states" -- would be associated an amplitude rather than a probability. Amplitudes yield probabilities -- the probability is the square of the absolute value of the amplitude -- but they do more; in particular, they can be negative. Indeed, they can be complex, but that they can be negative is usually enough. This allows one to do many more tricks with them, in quite a few ways, but in particular, it means that it's easier to set it up for the right answer to come out with high probability, because unlike probabilities, amplitudes can cancel out. All quantum algorithms, as I understand it, are about using appropriate tricks to get the amplitudes for the wrong answers to mostly cancel out.
ajb 15y ago
The easiest way of understanding quantum computing is to have a play with Oemer's QCL: http://tph.tuwien.ac.at/~oemer/qcl.html http://tph.tuwien.ac.at/~oemer/qcl.html
pooriaazimi 15y ago
Check this video out. I watched it many years ago, and was completely baffled by it (and still am): http://www.youtube.com/watch?v=DfPeprQ7oGc http://www.youtube.com/watch?v=DfPeprQ7oGc It's just 5 minutes. Well worth watching.

by readme 15y ago

Radzell 15y ago

I wrote a paper in highschool so take this with a grain of salt basically the idea is have truly parallel programming instead of having concurrent ones the ability of the qubit to solve for multiple states means they can solve for multiple problems at the same time while conventional computing seems parallel whats really happening is that calculation are switching states so fast they feel parallel. If I am wrong someone correct me.

exit 15y ago
did you also refrain from using punctuation in your report?
buu700 15y ago
Yeah, that's completely off (it would be a more apt description of the distinction between multiple cores and hyperthreading). The important characteristic of quantum computation is not that it's faster or more parallel than classical computation, but that it's a generalisation of classical computation. The same way that classical mechanics describes a subset of quantum mechanics rather than disjoint phenomena, all current classical CPUs are technically "quantum" CPUs (the best kind of quantum CPUs!). So, what does this mean? Well, for all the software we have today, and for almost everything we know how to code today, absolutely nothing; in fact, most of what we can do on classical computers will be slower simply because it will be quite some time before a quantum computer is anywhere near as well-engineered as, say, a Core i7 – especially when you take into account that the properties of quantum mechanics make this engineering not only different but also significantly more difficult. What we do get from the computational paradigm shift, however, is a broader set of operations which allow for a broader set of algorithms. Take Grover's algorithm (the one mentioned in the article): http://en.wikipedia.org/wiki/Grovers_algorithm#Algorithm_steps http://en.wikipedia.org/wiki/Grovers_algorithm#Algorithm_ste... If you understand the notation, what you'll see is a series of linear operations (quantum gates) being applied to vectors (qubits (classical bits are scalars)) in a quantum circuit. These can all be used to describe any operation which would be performed on, say, an x86 core (albeit more verbosely), but can also take advantage of quantum mechanical properties to manipulate non-classical information (which gets complicated to discuss). For the canonical example of how this can significantly change computation as we know it, see Shor's algorithm, which speeds up prime number factorisation from sub-exponential time to polynomial time, and thus could potentially break RSA encryption if we had a practical quantum computer): http://en.wikipedia.org/wiki/Shors_algorithm http://en.wikipedia.org/wiki/Shors_algorithm Aside from that, I'm sure people much smarter than I am could go on in technical depth about how, despite not really being an advancement of mythical proportions in and of itself, this new class of algorithms would be able to revolutionise areas like search, machine learning, physical/biological/chemical simulation, and so on.

betawolf33 15y ago

A rather quick answer from a not-totally-grasping person: the qubit stores all the possible resultant states of an interaction with it, and then collapses to one of those values when you measure it. So you can do processing really quick because you can do explore a buckload of possibilities at once. The physical reality of the phenomenon is hard to grasp, and I'm still not totally sure I get/buy it. See http://en.wikipedia.org/wiki/Double-slit_experiment http://en.wikipedia.org/wiki/Double-slit_experiment

rbanffy 15y ago
It's said one cannot understand quantum mechanics. Humans can merely get used to it.
- trafficlight 15y ago
  I've read the Wikipedia pages on Quantum Computing and qubits a few times and all I can say is, "Yes, mmhmm, yes. I know some of these words." I wonder if computing, and other sciences, will become so advanced that fewer and fewer people will be able to comprehend the fundamentals or will there be a time when things like quantum mechanics are a high school subject?
  - rprospero 15y ago
    Basic quantum mechanics could be a high school subject. While solving the hydrogen atom might be out of their reach, some simple angular momentum operators and Clebsh-Gordan tables shouldn't be beyond the reach of a sophomore.
    - greeneggs 15y ago
      Basic quantum mechanics should be a high-school subject. The way physicists teach it currently, based on its historical development instead of on the modern understanding, is tragic. It just makes everyone repeat that nonsense quote, that nobody understands quantum physics. Teaching angular momentum and Clebsch-Gordan coefficients seems pointless. There should be a standard class on probability theory and statistics. Quantum theory should be introduced as a generalization of probability theory. This is the right foundation for the field, not some vague and basically meaningless statements like particles are both particles and waves.

mathgladiator 15y ago

imagine an 2-qubit unsigned integer being all four permutations at once, then you add 1, now you have manipulated all permutations at once. However, the trick is that you haven't done anything yet. So, we need new algebras to collapse wave functions in interesting way.

Sniffnoy 15y ago

I would say this explanation is essentially wrong. It makes it sound like the difference is that the computer is ternary rather than binary, which of course would not be a significant difference. Part of this is that the "more than one state at at time" applies to the whole computer, not individual bits, but the thing is that the whole "more than one state at a time" thing isn't it either. To see this, instead of a quantum computer, let's consider a probabilistic computer. Rather than having one state, the computer at any time has a probability distribution over states -- it can "be in multiple states at once", each with some probability. Only at the end of a computation do you "collapse" it back into a single value. Except that such a computer is equivalent to an ordinary computer equipped with a TRNG, which is not much more powerful than an ordinary computer at all. Quantum computers are often described as "trying everything at once", as if they were nondeterministic Turing machines, but they are not; perhaps, in some sense, they do try everything at once, but they cannot then automatically pick out whichever possibility worked. It only "tries everything at once" in the same sense the probabilistic computer does. The probabilistic computer can only pick out the right answer if you somehow set it up that the right answer has high probability and the wrong ones don't; it can't say "this answer is right, kill all the other possibilities now!". The quantum computer is the same way. What makes quantum computers faster is the fact that instead of probabilities, they use amplitudes. To each state -- well, what I was calling states above, really they would be "basis states" -- would be associated an amplitude rather than a probability. Amplitudes yield probabilities -- the probability is the square of the absolute value of the amplitude -- but they do more; in particular, they can be negative. Indeed, they can be complex, but that they can be negative is usually enough. This allows one to do many more tricks with them, in quite a few ways, but in particular, it means that it's easier to set it up for the right answer to come out with high probability, because unlike probabilities, amplitudes can cancel out. All quantum algorithms, as I understand it, are about using appropriate tricks to get the amplitudes for the wrong answers to mostly cancel out.

ajb 15y ago

The easiest way of understanding quantum computing is to have a play with Oemer's QCL: http://tph.tuwien.ac.at/~oemer/qcl.html http://tph.tuwien.ac.at/~oemer/qcl.html

pooriaazimi 15y ago

Check this video out. I watched it many years ago, and was completely baffled by it (and still am): http://www.youtube.com/watch?v=DfPeprQ7oGc http://www.youtube.com/watch?v=DfPeprQ7oGc It's just 5 minutes. Well worth watching.