MIT And HP Announce Joint Quantum Computer Project

MetaCow writes: "CNN is running this article which describes a joint effort between MIT and HP to build a quantum computer. Nothing expected any time soon, though: 'Quantum computing research is farsighted, and it may take 10 years to develop a fully operational quantum computer ...'"

Comments

Some real info...article lacks it

[akiaki007]

Quite a lame article, IMO.

The article fails to make any real points. It's merely a PR article for HP and MIT.

Unlike classical bits, the qubit can be not just 0 or 1 but a superposition of both, in differing proportions.

Um...wrong. The qubit can be in the 0 or 1 state, but can also be both at the same time, and have varying rotations. Which is what makes it immpossible for us to decode them. It is the multiple state position that is what is interesting to us, and what does the parallel computing. We just don't know how to utilize it just yet. There have been various articles. Quibit.org is a great place to start reading up on this stuff. The IBM Almaden has a nice article that will actually tell you something useful.

Re:Some real info...article lacks it

[internic]

I also thought the article lacked a lot of relevent info and, what's more, said some things that were just wrong. A few additional pieces of information that might be of interest:

A quantum computer is not simply faster than a classical computer

Quantum computers use a different set of fundemental logical operations, which allow them to do all the things a classical computer (Turing machine) can, plus it allows some other operations to be done using the superpositions or entaglement of states. This means there are some problems for which fundementally different algerithms can be written to do it much faster, in polynomial time as apposed to exponential; however, there are just a few of these. There's no reason to think it will be faster for everything. For most tasks odds are its algerithms will be just as efficient as a classical computer. In addition, its logic operations will likely be slower meaning it may well be slower for the vast majority of tasks. So, don't expect a desktop QC in 20 years, it would probably be used only for specialized computational tasks for the forseable future.

A quantum computer is not right around the corner

Though the article gives little detail, the computer they're talking about making in 10 years will probably not be amongst the most powerful in the world when it is turned on. Odds are it will be more like the size of house with the power of a pocket calculator, old school mainframe style. This is due to the difficulties they mention. This is not really made very clear in the article, but the difficulties they face aren't just practical. Even theoretical calculations suggest that it's not feasible with currently theorized techniques to make a quantum computer more than about 100 qubits, due to decoherence and computer control factors. Quoth one paper, "...the absolute limit on what any practical NMR comptuer can handle remains well below 100 bits" (Cory et al., Proc. Natl. Acad. Sci. USA 94, 1997). I've read similar estimates for all forms of quantum computation currently in the works. It seems that it takes a computer with on the order of 500 to 1000s of qubits before it actually becomes more useful than a classical computer. This should not be hard to imagine. What do you think you could do with a computer that could only hold 100 bits of memory at a time? The point is that in ten years, we won't be seeing any supercomputer.

Quantum computers are not the next step in miniturization

The article says that we're reaching the limit of classical computation and suggest that quantum computers are the next step. It is true that Feynmann suggested in his original paper on the topic in 1983 that when computer technology reached the atomic scale then quantum mechanics would have to become part of computation, but quantum computers as they are talked about today have little to do with miniturization. In many of the schemes, such as atom traps quantum computers, the memory and computation elements (when control devices are included) are much larger than those for classical computers. This can also be said for RF-Squids and quantum dots. In short, the proimise of quantum computers has nothing to do with miniturization, it has to do with the fact that they can perform fundementally different algerithms.

All that being said, I think it is a good that they're doing this research, and I do think that quantum computers will likely someday be useful, both as computers and as tools for researching quantum mechanics further. I am not saying I don't think they'll work, simply that the article seems to suggest a picture which is overly optimistic. However, with the great promise they hold, I don't think we can afford not to do research like this.

Re:The Quantum Computing Swindle

[Anonymous Coward]

There exists an entire sub-culture who believe in the Great Conspiracy and those who try to refute QM are no different, tilting at windmills while the rest of us get on with our lives and work with with the best available evidence. Ultimately, the anti-Non-Locality folks have to believe in a grand conspiracy of nature to make their ad hoc models even come close to reproducing the non-local correlations observed in quite a few experiments (using different systems, methodologies). We have had experiments which closed the locality loophole (Gisin, Geneva), experiments which closed the detection loopholes (Wineland, Boulder), and there are proposals to close both at the same time.

As new experiments are done, improving on the previous ones, the results merely confirm the predictions of QM, no sign of deviation from what we should expect. Not to mention that QM is the basis of electronics, which seems to work to a remarkably high degree, for a supposedly `wrong' theory. I see a parallel to the `Creation Science' debacle, where anti-evolutionists play their `argument from incredulity' card and try to poke holes into a straw man of their devising. Those rejecting the established results of QM are our latter-day Flat Earthers. I admire their ability to perform logical and factual contortions to support their untenable position.

As for the funding situation, the amount of money spent on Quantum Computation is mere loose change, just enough to keep mainly theoreticians lean and mean, with a few small scale experiments running (we're not talking SSC here). A 10 year time-line for the development of a fully functioning quantum computer is a stretch though, the technical challenges are very formidable, and it may follow the Fusion Power story. Still, the fundamental research in Quantum Information Theory is still very worthwhile in its own right, whether or not we can build a scalable quantum computer. The outlook for quantum crypto is much better, commercialised systems may come out within a 10 year horizon.

Sure, there is a lot of hype, and I cringe everytime I read a popular account of QC for all the misunderstandings promulgated, but it is a very serious research programme. Through considerations of quantum information, we may find a way of unifying the two great pillars of modern physics, GR and QM.

Re:Wait, wait.. a "computer"?

[Insount]

These are excellent questions. I'll try to answer them as far as my knowledge of the field allows, but please bear in mind that a good answer to some of the issues you raised would significantly enhance our state of knowledge.

First, two key facts.

• A quantum computer can run any classical algorithm. There is some overhead due the reversibility constraint and due to the practical need for error correction, but it's probably a low-order polynomial overhead at worst. In particular, a quantum computer can run a Universal Turing Machine. So, it's fully programmable in respect to classical programs.
• There exists a Universal Quantum Turing Machine that acts analogously to a classical Universal Turing Machine, i.e., lets a fixed quantum computer simulate run any quantum algorithm given a description of that algorithm as additional input. (It does so to finite accuracy, but the error can be made arbitrarily small)

So yes, we're talking about a fully programmable computer. However, this universaily means an increase in the computer size, so for practical reasons you'll see two shortcuts that undermine this universatily.

First, everything that can be done classically is done outside the quantum computer -- a quantum-classical dualism, if you wish. Suppose you have an algorithm that performs operation Q on some register, and applies it 200 times in a loop. You could put the loop counter as part of the quantum computer and program it to do an increment+test+Q operation. However, currently it's much cheaper to put the loop counter outside the quantum computer and simply tell it 200 times to apply a Q operation.

Second, the hardware is made as simple and specialized as possible, and optimized for a specific algorithm.

Now, these shortcuts are clearly present in the tiny quantum computers built so far (latest is IBM's, featuring 8 qubits), and will probably be used for quite some time. But that's mere practice, not theory.

OK, so how do you program this things? All quantum algorithms to date have been expressed using one of two formalisms: either using algebra in the mathematical "Hilbert space" that represents all the states the computer can be in, or using a "quantum circuit" which is just like a normal logical circuit (with gates like AND and NOT), except the gates are different -- in fact the gates are expressed as operations in the Hilbert space, as in the first approach, but it's often easier to see the overall picture if you combine simple gates using the circuit formalism. To be truthful, there's also the "and then you do that N more times, and then you measure first register" type of formalism. :-)

So you see, currently researchers are working at a level way below assembly language, and they're pretty happy about it because the algorithms are very small too. But what about higher-level representations? All efforts I've seen so far use quantum-classical dualism: you write a classical program that manipulates a quantum register (data), but the logic is purely classical. Some do it with a dedicated programming language, some with a class library, but the idea is the same (see a comprehensive list; all of these are mere simulators for now, of course).

Now, this is a very reasonable approach, but it seems rather halfway-there -- wouldn't it beneficial to allow quantum operations in flow control, not only in data? Well, we don't know yet. Currently there are very few "patterns" used in quantum computing, and none of them seems to easier to represent that way. It's hard to design a paradigm, let alone a language, for solving problems that don't yet exist. On the other hand, if we invent such a paradigm it might help us find new quantum algorithms. This is a vast open research area.

As for your speculations on how quantum computers will be used, the answers is yet again that we don't know. Here are the two extreme cases, both easily imagined and consistent with current knowledge. First, it could be that quantum computers will be found to be good for nothing except a few very specialized tasks, and that only a few RSA-cracking devices will be built by intelligence agencies at a prohobitive cost. On the other hand, it could be that a new class of quantum algorithms will be discovered that address more common needs, leading first to something in the college basement and later to a chip in everybody's computer. No one currently knows such these chips can be good for, if at all, though there's some intuition about what's more likely. I do venture to say that which of these possibilities becomes reality depends primarly on usefulness, since long-term prospects for mass-producton seem quite real, given sufficient demand.

I hope this clears things up a bit. I wish I could be more concrete, but it really takes a few hours to get a rough grasp of how these things really work, and a full-semester course to understand the interesting algorithms. Please don't hesitate to e-mail me if you want to discuss this further.