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First Quantum Computing Gate on a Chip

Posted by Zonk on from the next-advance-is-really-tiny-stargates dept.

An anonymous reader writes "After recent success in using quantum computing for superconducting qubits, researchers from Delft have formed the first Controlled-NOT quantum gate. 'A team has demonstrated a key ingredient of such a computer by using one superconducting loop to control the information stored on a second. Combined with other recent advances, the result may pave the way for devices of double the size in the next year or two--closer to what other quantum computing candidates have achieved, says physicist Hans Mooij of the Delft University of Technology in the Netherlands. Unlike today's computers, which process information in the form of 0s and 1s, a quantum computer would achieve new levels of power by turning bits into fuzzy quantum things called qubits (pronounced cue-bits) that are 0 and 1 simultaneously. In theory, quantum computers would allow hackers to crack today's toughest coded messages and researchers to better simulate molecules for designing new drugs and materials.'"

6 of 166 comments (clear)

  1. Double the size of a single not gate? by Spazntwich · · Score: 5, Funny

    I know grammar has been taking a hit in society as of late, but now even our computers are blatantly spewing out double negatives?

    We're not in for an unrough ride, gentlemen.

  2. A solid milestone... by teebob21 · · Score: 5, Interesting

    I find it interesting that the first electronic computing gates devised were the AND/OR gates, using basic diode logic. Quantum computing research develops the NOT gate first. I think this has something to do with the esoteric nature of quantum computing. AND/OR gates require two inputs to change to a single value, where NOT is merely an inverter. The idea of entanglement makes the inversion process a likely first step in quantum research.

    For those wondering why this is important, the first true electronic gates were invented in the early 1920's. This predates point-contact transistors by about 20 years, invented in 1947. 60 years later, here we are with transistor computing in every aspect of our lives.

    At the rate quantum computing is advancing, I think we can expect to see quantum transistors (in the lab, at least) by 2020. A true useful quantum computer may be available less than 50 years from now. Hopefully by then someone will pick up the slack and have the Linux kernel ported to the Q-CPU architecture!

    --
    khasim (12/9/06): In a blind taste test, more people preferred Coke over the Pepsi that I had previously pissed in.
    1. Re:A solid milestone... by pablob · · Score: 5, Informative

      I find it interesting that the first electronic computing gates devised were the AND/OR gates, using basic diode logic. Quantum computing research develops the NOT gate first. I think this has something to do with the esoteric nature of quantum computing. AND/OR gates require two inputs to change to a single value, where NOT is merely an inverter. The idea of entanglement makes the inversion process a likely first step in quantum research.

      Keep in mind that this is a Controlled-NOT gate (a two-input gate) and not a simple NOT gate (a one-input gate). It has been proven that if you can implement two-qubit C-NOT and arbitrary one-qubit operations, you can implement a universal quantum computer (that is, one that can run an arbitrary "quantum program").

      There is a deeper reason for quantum computers not to use AND/OR gates, which is their irresibility (AND and OR are two-input to one input gate, which makes them irreversible). Quantum Mechanics is intrinsically reversible, so a quantum computer should be reversible too and that's why it is not common to hear about Quantum AND or Quantum OR.

      Pablo B.

    2. Re:A solid milestone... by asuffield · · Score: 5, Interesting

      For those wondering why this is important, the first true electronic gates were invented in the early 1920's. This predates point-contact transistors by about 20 years, invented in 1947. 60 years later, here we are with transistor computing in every aspect of our lives.


      However, it is important to realise that the theory of computation had been in development since the early 1800s (and the logic underlying that had been around for centuries); by the time the first electronic devices were created, we already had a good understanding of what they could be used for, because we had been doing exactly the same things by hand for over 50 years at that point (the word "computer" originally meant a person who performed such computations, and an "electronic computer" was just a device to replicate the task that person was doing).

      We can't do quantum computations by hand, so we have no real experience with the theory, and the underlying statistical methods are relatively recent developments: quantum computers do not use the classical logic that we're all familiar with. This is a massive setback compared to the development of the electronic computer - and advances in theory usually can't be accelerated all that much. It is likely to be between 50 and 100 years before we know enough to build non-trivial applications out of quantum computers. Not because we can't build the hardware, but because we don't know how to write any software to run on them. The entire field of software development will have to be reinvented, and we don't actually know that it will be useful for anything. Unlike the first electronic computers, which had very real and obvious applications performing the tasks that were currently being done by hand, we have only vague theories and ideas about what quantum computers might be useful for. (Even the much-quoted method for breaking certain encryption algorithms is based on various assumptions that aren't proven; we don't know for sure whether quantum computers will actually be able to run it, yet)

      We'll get there eventually, but it will probably take a long time and we can't really predict at this stage whether it'll be particularly useful. From what we know so far, these things are going to be incredibly arcane and obtuse to work with, and that is going to make it difficult. We might see it in our lifetimes, but I wouldn't place any bets on it, it might take much longer. The things we're playing with today may turn out to be the Babbage engines of quantum computing.
  3. Quantum gates? by Mikachu · · Score: 5, Funny

    They're opening the quantum gates now? They're insane! Who knows what might pour out of them... I hope they're at least doing it on the moon.

    The future of the human race is up to one lone marine now. Thanks a lot, scientists.

  4. Re:Quantum states by mindriot · · Score: 5, Informative

    Note: I am not a physicist, this is just what I remember from a quantum computing lecture I attended years ago. Of course, rather than believing 100% in what I wrote, you're probably better off double-checking on Wikipedia and Google...

    The quantum states you're referring to do have something to do with this. However, their number isn't what's important.
    The interesting thing about the quantum computing world is that such states can be in superposition, that is, it is unclear whether or not the state is one or the other. You can only know that if you measure the state, the outcome will be state A in, say, 30% of the time, and state B in 70%. Now, you could probably extend this to 32 different states, but since we're used to bits, we'll build something where we just use two (for instance linearly polarized photons -- 0 degrees = 0, 90 degrees = 1).

    Now, there exist methods (or they're being researched) that allow you to put your bit into a superposition of its states. This could, for instance, be so that measuring the state will produce a 0 exactly half the time. Maybe you could put your Schroedinger cat in the box -- dead=0, alive=1...

    This by itself is not particularly exciting. But you could do that for multiple bits (say a 32-qubit word) so that measuring it, you get uniform probability to measure any number between 0 and 4294967295. Where it really gets interesting is when you apply quantum operators to your state: They can transform the state without destroying the superposition, i.e. without measuring it. For instance, if your superposition currently gives you 30% chance for measuring a 0 and 70% for a 1, then a CNOT gate would reverse that probability.

    Note, however, that a CNOT is a "controlled not": it has two inputs, the control and the target. The control passes through unchanged, but the target is flipped if and only if the control is 1 (i.e. the target output value is identical to the XOR of the input values). In a quantum world, this lets the two bits be entangled: For instance, if the target bit is 1, then the output of the target is 1 iff the control is 0 (target = NOT control). Now suppose that we create a superposition on the control input -- then the control output will be that same superposition, but the target output will be (NOT control) for all control values. In other words, we've just computed a function for all possible input values at once. And you can build these things larger, to do more useful things, such as with a 32-qubit input.

    The problem is, you thus get all possible results at the same time, but it's a superposition, and after measuring, you'll only have one result. Why is this useful? Because for one, you can construct some algorithms that transform the problem in such a way as to give a guaranteed result; in other cases, you'll do multiple samples and after a while you'll get your result -- and for some problems, you'll get it orders of magnitude quicker, on average, than on classical computers.

    For instance, the Deutsch-Josza algorithm is such an example. Assume I have a function that does one of two things -- it is either constant over the whole input domain, or it is balanced, that is, it returns 0 for exactly half the possible inputs and 1 for the other half. The function, to you, is a black box. How do you determine quickly whether the function is constant or balanced? On a classical computer, you have to test one more than half the inputs, in the worst case, to find out whether the function is balanced or constant. Using the Deutsch-Josza algorithm, you can solve the problem in *constant* time on a quantum computer.

    In other words, quantum computing may be interesting for some number-crunching applications. Of course the true capabilities of such a system are not yet completely understood. But I would think that for desktop computing it's probably not too relevant...