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Under the Hood of Quantum Computing
nanotrends writes "Gordie Rose, the CTO of Dwave Systems, the venture funded company that plans to offer paid use of a superconducting quantum computer starting in 2007, reveals secrets of his quantum computer construction. It is based on nobium superconducting 'circuits of atoms' and is not RSFQ. (Rapid Single Flux quantum)."
I read the article, but it didn't make it very clear - what will be the advantages of paid use of their quantum computer? Unless it's going to be faster than other supercomputers, I can't see the point.
Well, it's a quantum computer. Given the problem it might be like trying to make your CPU compete against a GeForce or ATI. If you try to do it all with CPU emulation, there's not much doubt who'll win. That said, I got the impression that current quantum computers have a so limited number of qbits (the computing power pretty much grows to 2^n with n bits), that it's faster and cheaper to just cycle through all 2^n possibilties one at a time. Currently the largest I've seen is a 12 qbit computer. Now 2^12 = 4096 states at once is a nice curiosity but nothing that makes my encryption keys worry. Basicly it's man vs Deep Blue at computer again - the quantum computer is great at testing many solutions at once but the sheer computing power of traditional computers takes home the victory. Now, if they can get hundreds of qbits together things will change massively. But the difficulty in keeping all those in a cohesive quantum state also raise drastically, so I think we're far off from a usable quantum computer.
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... What have I missed here?
For starters; a link to the company's website instead of somebody's "See Spot run" blog post:
http://www.dwavesys.com/quantumcomputing.php
KFG
From dwave's site: "There are many potential ways to build quantum computers (QCs). Of these, four types have emerged as being most likely to succeed. These are based on (A) assemblies of individual atoms trapped by lasers; (B) optical circuits, for example using photonic crystals; (C) semiconductor-based designs, usually including atomic-scale control of dopant atom distribution or quantum dots; and (D) superconducting electronics. D-Wave focuses exclusively on superconducting electronics. This is because superconductors have the unique property that very large structures can be built out of them that behave according to the rules of quantum mechanics. Because of this, design of superconducting QCs does not require new technology development. This is in contrast to the other three types of QCs, in which information is stored using atoms or individual photons (particles of light), and controlling and manipulating this information requires technologies that do not yet exist. The two superconductors used to build QCs are aluminum and niobium. At room temperature these materials are metals. When they are cooled down close to absolute zero, the electrons in the metals pair to form particles called Cooper pairs. These particles carry charge in the superconductor. Cooper pairs are very different from electrons. One key difference is that Cooper pairs are what physicists call bosons, while electrons are fermions. Bosons are allowed to occupy the same quantum state, while fermions are not. In a superconductor, all the Cooper pairs can (and do) exist in exactly the same state. This means that all of the charge carriers in the superconductor are fundamentally linked. They directly inherit their behavior from the scale of a single Cooper pair. One way to think of this is that a chunk of superconductor amplifies the quantum effects that exist at the level of extremely tiny individual particles up to the scale of the whole chunk, even if the chunk is very large. This amplification of quantum effects is responsible for the well-known properties of superconductors, such as zero resistance to current flow and exclusion of magnetic field. It is also extremely useful for building components of QCs. Superconductors naturally shield themselves from external noise, creating a safe haven for quantum effects. This ability to build large things that behave like small things overcomes many practical problems in building real QCs."
I think the point of the article is that D-Wave Corp claims to be able to create qbits from "large" objects (ie; large enough to be fabricated using standard IC fabrication techniques), but with niobium rather than silicon. This enables them to create a quantum computer without all the hassle of having to manipulate individual atoms as the present research lab quantum computers do. From the article:
Since supercooling is required, it's highly unlikely that you or I will be able to afford one of these things any time soon (assuming it's not all marketing hype in the first place), but you can be assured the NSA and other government "intelligence" agencies will be able to afford as many as they want because of all the tribute they demand from us on pain of imprisonment, in the form of exorbitant taxation.
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From what has been described on the blog and website, i'm not convinced that what they're working on is much more than simply a superconducting RSFQ - Rapid Single Flux Quantum - chip, which although can concievably run at a breakneck speed compared to todays Silicon CPU's, is not a Quantum Computer in the normal sense. This thing isn't going to run Shor's Algorithm. Also, i'm surprised to notice that there are people here who still consider QCs as science fiction - they're not. Quantum Computing has been practical in the lab since the 90's - and, for example, composite numbers have been factorised in polynomial time. The challenge faced by QCT research groups around the world at present is mainly building the things with a large number of qubits, and still maintaining successful operation. With regards to solid state devices such as the Kane QC model, one of the approaches being investigated involves building multiple small QCs and interconnecting them via conventional microelectronics - perhaps SETs, RSFQs, spintronics or maybe even plain old silicon microelectronics - to create a useful, many-qubit, computer.
As far as I know, only RSA-style cryptograophy is affected by quantum computing. There are other ways to do public key encryption, such as elliptical curve cryptography that should be unaffected, as they depend on a different class of problem being hard, and of course quantum computing won't help with symmetric key crypto at all.
The NSA has been advising the security community against using RSA-style encryption for some time now - it's not like they're trying to keep the weakness a secret for some nefarious reason.
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I do believe you're mistaken. Quantum bits are exactly like regular bits in their possible observable states - that is, they are either "on" or "off" when observed. The interesting part of quantum computing comes from the fact that, when they're not being observed, they exist in a superposition of both "on" and "off" states. Now, if you put 8 of these bits together, you have a 'qbyte' which, while when it's observed it can only represent the same range as a regular byte, can be used in calculations representing every single possible permutation of the data at once - i.e. every number from 0 through 255. Each bit you add doubles the number of states you can simultaneously test using this superposition property - this is what the GP meant when he said that quantum computing scales as 2^n.