Slashdot Mirror
Quantum Computers
joecool12321 writes: "Although Richard Feynman spoke about quantum computers in 1981, technology is only now starting to catch up. This article at Scientific American discusses recent developments towards the goal of 'infinite computing,' and research is showing that scalibility may not be far away, and thus scalable qbits."
I remember seeing something about atom trapping. I was able to find a tone down version of the Science magazine article here: www.academicpress.com/inscight/06022000/graphb.htm
Schmiedmayer, who's mentioned in the parent story, is also in this story from mid-last year.
A recent slashdot article that I submitted also concerns the aspect of using silicon buckyballs as cages for qubits.
The crux of the matter still remains unsolved in this SciAm article, and I have yet to see any explanation on how to solve it in any of the scientific journals that I read: that is, we don't use pure quantum states to preserve the very fickle quantum condition. When we can do that - there have already been enough postulation on what a qubit can consist of - then we can seriously consider quantum computing in the future.
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I'm just an ordinary man with nothing to lose.
First, I'd like to point out that quantum computation and quantum encryption are two almost completely separate concepts. Quantum encryption is based on the fact that quantum states cannot be measured without altering. The most common example is the polarization of a photon, but it will work for any quantum state, so long as there exist, effectively, two unique states that can transmit the data.
Quantum computation, however, is much more complex and much more interesting. Quantum computers are based on the concept of quantum entanglement, the ability of a quantum state to exist in a superposition of all of its mutually exclusive states: It's a 1 and a 0. However, this is not as easy to use as one might think. While it's true that if you have n quantum logic gates you have the ability to input 2^n data values simultaneously (as opposed to only 1 piece of data if you have n digital logic gates), this is not going to be the end of classical computing for a few reasons. First, quantum computers have to be perfectly reversible. That means for every output there's an input and vice versa. And there has to be no way of knowing the initial states of the data. You don't process data, you process probabilities in a quantum computer; if you know exactly what any one value is throughout the computation, you can find out all of the values: the superposition ends and you're stuck with a useless chunk of machinery. This means YOU CAN ONLY GET ONE RESULT FROM ANY QUANTUM COMPUTATION, THE END RESULT. You can't see what the data in the middle is or the computer becomes useless. (Landauer's principle makes heat loss data loss. When your processor gets hot, it's losing data. If the same thing happened to a quantum computer, it wouldn't be quantum anymore.) Decoherence is what happens when you randomly lose data to the environment by design, not by choice, and the superposition ends. This is bad for Q.C. Oh, and quantum computers can only do *some* things faster, like prime factorization and discrete logarithms. Not multiplication or addition. Plus, the circuits that would do basic arithmetic would be bigger and slower than what you've currently got.
So what does this all mean? It means that quantum computers are going to provide some advantages (real quick big number factorization), and some disadvantages (that whole RSA standard). The most realistic initial use of quantum computers will be as add-ons to existing super-computers to resolve certain types of NP-Complete headaches that regular math can't simplify yet. At best they will someday be an add-on to your PC; but they will never replace the digital computer.~
If you want more info, check out ahttp://www.qubit.org, it's got some decent tutorials.