Quantum computing infeasibility due to quantum tomography?

[mok-kong shen]

It seems that both quantum error correction and quantum tomography are necessary for practical realization of quantum computing, since the hardware needs to be verified for correctness in design, manufacture and maintenance. Is that true? If yes, then since, according to Wiki, quantum tomography is practically infeasible for cases of more than a few qubits due to exponential increase of work with the number of qubits, the practical infeasibility of quantum computing would be a direct consequence IMHO.

[Joy Christian]

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You raise a good question and I do not wish to distract from it, but there are also more fundamental reasons for the non-viability of quantum computing, as discussed, for example, in this entertaining review of a book by a staunch proponent of quantum computing: http://www.amazon.com/review/R2NDP5WIYU ... r_rdp_perm
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[FrediFizzx]

It seems that both quantum error correction and quantum tomography are necessary for practical realization of quantum computing, since the hardware needs to be verified for correctness in design, manufacture and maintenance. Is that true? If yes, then since, according to Wiki, quantum tomography is practically infeasible for cases of more than a few qubits due to exponential increase of work with the number of qubits, the practical infeasibility of quantum computing would be a direct consequence IMHO.

The D-Wave system is probably the closest they will get to a QC. As Joy pointed out, there is a more fundamental reason why they won't be successful.

viewtopic.php?f=6&t=212

[minkwe]

https://en.wikipedia.org/wiki/D-Wave_Systems

A study published in Science in June 2014, described as "likely the most thorough and precise study that has been done on the performance of the D-Wave machine"[54] and "the fairest comparison yet", found that the D-Wave chip "produced no quantum speedup".[55] The researchers, led by Matthias Troyer at the Swiss Federal Institute of Technology, found "no quantum evidence" across the entire range of their tests, and only inconclusive results when looking at subsets of the tests. Several possible explanations were suggested. 1) Perhaps quantum annealing (the type of problem for which the D-Wave machine is designed) is not amenable to a speedup. 2) Perhaps the D-Wave 2 cannot realize a quantum speedup. 3) Perhaps the speedup exists but is masked by errors or other problems.[56]

[FrediFizzx]

And... not very close at all. But experimenters are very clever; they may find a way to take advantage of non-linear correlations eventually but doubtful there will be much speedup.

[minkwe]

A "gullible audience" or "clever magician"? The result is the same. I pick the former.

[Joy Christian]

A "gullible audience" or "clever magician"? The result is the same. I pick the former.

As some of you may know, there are much more sinister things going on than just the gullibility of the audience or cleverness of the magicians. Any paper that tries to challenge the prevalent dogmas is stonewalled fraudulently (as Richard Gill stonewalled my paper submitted to Nature), or attacked disingenuously (as Richard Gill tried to have my paper retracted from IJTP using bogus criticism), or the author of the paper is deprived financially (as Scott Aaronson managed to have my funding from FQXi blocked using his personal friendship with the directors of the institute). These are just a few examples of the dirty underhand tactics and political tricks being used by those addicted to mysticism within physics. I wish I was just being cynical but unfortunately these are all facts for which I have documentary evidence.

[FrediFizzx]

http://www.marketwired.com/press-releas ... 072670.htm

Labs are still buying the D-wave system for some reason. ??? Perhaps because even though there is no speedup, they use less power than other super-computers?

[Joy Christian]

http://www.marketwired.com/press-release/los-alamos-national-laboratory-orders-a-1000-qubit-d-wave-2x-quantum-computer-2072670.htm

Labs are still buying the D-wave system for some reason. ??? Perhaps because even though there is no speedup, they use less power than other super-computers?

Yes. Although theirs is not a "quantum" computer (as we know, there is never going to be one), they have been able to make some computations faster than before.

[Joy Christian]

http://9to5google.com/2015/11/11/google ... ecember-8/

[mok-kong shen]

I just want to say that I have in the meantime collected from some books a number of IMHO interesting passages that are relevant to my OP and posted them at http://s13.zetaboards.com/Crypto/topic/7457176/1/

[Joy Christian]

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Some somber thoughts on the infeasibility of quantum computing: http://www.huffingtonpost.com/steven-ji ... 04846.html

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[Q-reeus]

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Some somber thoughts on the infeasibility of quantum computing: http://www.huffingtonpost.com/steven-ji ... 04846.html

***

A recent article that appears very well balanced concludes there is finally evidence of some, limited substance to D-Waves claims after all:
http://arstechnica.co.uk/science/2016/0 ... -computer/

Someone critical of QC claims that I consider to be a true genius - http://engineering.tamu.edu/electrical/people/lkish
In addition to the points raised in first post here, he has outlined a spectrum of issues that collectively scuttle the heady claims of optimists:
http://www.ece.tamu.edu/~noise/research ... dissip.htm

At the same time, Kish maintains that noise can be the basis of actually achievable exponential computational speed up. An amazing claim, but then he and collaborators have already achieved noise-based unconditionally secure key distribution systems that beat quantum systems in all departments. Hence I'm not about to bet against him on the noise-based computation claims.

[Joy Christian]

Canada's Prime Minister has provided a great boost to the popularity of the quest for a "quantum computer." He was talking at the Perimeter Institute in Waterloo, Canada (where I was once a Visiting Professor for two years). The Prime Minister not only impressed both the journalists and the scientists at the institute, but also pledged $50 million of ongoing state support for research on quantum computing. You can watch him impress here: https://www.youtube.com/watch?v=4ZBLSjF56S8.

This reminds me of a funny story I read in an arXiv paper a few years ago about how to get a grant to teach a donkey how to read: http://arxiv.org/abs/1212.3562.

Let me quote from this paper:

The [Quantum Computer] story says a lot about human nature, the scientific community, and the society as a whole, so it deserves profound psycho-sociological studies, which should begin right now, while the main actors are still alive and can be questioned.

A somewhat similar story can be traced back to the 13th century when Nasreddin Hodja made a proposal to teach his donkey to read and obtained a 10-year grant from the local Sultan. For his first report he put breadcrumbs between the pages of a big book, and demonstrated the donkey turning the pages with his hoofs. This was a promising first step in the right direction.

Nasreddin was a wise but simple man, so when asked by friends how he hopes to accomplish his goal, he answered: “My dear fellows, before ten years are up, either I will die or the Sultan will die. Or else, the donkey will die.”

Had he the modern degree of sophistication, he could say, first, that there is no theorem forbidding donkeys to read. And, since this does not contradict any known fundamental principles, the failure to achieve this goal would reveal new laws of Nature. So, it is a win-win strategy: either the donkey learns to read, or new laws will be discovered.

Second, he could say that his research may, with some modifications, be generalized to other animals, like goats and sheep, as well as to insects, like ants, gnats, and flies, and this will have a tremendous potential for improving national security: these beasts could easily cross the enemy lines, read the secret plans, and report them back to us.

[Joy Christian]

Here is another sceptical paper on "quantum computing" by the same author: http://arxiv.org/abs/1401.3629

Prospects for quantum computing: extremely doubtful

Abstract:

The quantum computer is supposed to process information by applying unitary transformations to complex amplitudes defining the state of qubits. A useful machine needing or more, the number of continuous parameters describing the state of a quantum computer at any given moment is at least which is much greater than the number of protons in the Universe. However, the theorists believe that the feasibility of large-scale quantum computing has been proved via the “threshold theorem”. Like for any theorem, the proof is based on a number of assumptions considered as axioms. However, in the physical world none of these assumptions can be fulfilled exactly. Any assumption can be only approached with some limited precision. So, the rather meaningless “error per qubit per gate” threshold must be supplemented by a list of the precisions with which all assumptions behind the threshold theorem should hold. Such a list still does not exist. The theory also seems to ignore the undesired free evolution of the quantum computer caused by the energy differences of quantum states entering any given superposition. Another important point is that the hypothetical quantum computer will be a system of qubits PLUS an extremely complex and monstrously sophisticated classical apparatus. This huge and strongly nonlinear system will generally exhibit instabilities and chaotic behavior.

[thray]

Hi Joy,

Key statement: "This huge and strongly nonlinear system will generally exhibit instabilities and chaotic behavior."

Quantum computing based on entanglement purports to control the uncontrollable. Better to let the function continue to connected subsystems for optimum results.

Best regards,

Tom

[mok-kong shen]

By chance I saw a paper: B. M. Terhal, "The Fragility of Quantum Information?" (arXiv:1305.4004V2) but barely understand its content due to my poor knowledge. Could someone kindly say something about that article?

[mok-kong shen]

As an aside, a 1 billion Euro project has been announced by the European Commission aimed at developing quantum technologies over the next 10 years. See http://europe.newsweek.com/quantum-comp ... 2167?rm=eu

[Dirkman]

How about this ? It's IBM, its a big private company, it wouldnt mess around with it's money.

"How IBM’s new five-qubit universal quantum computer works"

http://arstechnica.com/science/2016/05/ ... ter-works/

[Joy Christian]

How about this ? It's IBM, its a big private company, it wouldnt mess around with it's money.

"How IBM’s new five-qubit universal quantum computer works"

http://arstechnica.com/science/2016/05/ ... ter-works/

There are fools everywhere. There is politics everywhere. There is opportunism everywhere. No one, IBM or no IBM, wants to be left behind the lucrative hype.

They write: "This might sound like some kind of publicity stunt; maybe it's IBM's way of clawing some attention back from D-Wave's quantum computing efforts."

They should have stopped writing right there. Calling something a "quantum computer" does not make it a quantum computer. It is anything but a quantum computer.

So don't be fooled by the IBM trick for a second. Next time wake me up when you have a commercially viable laptop that exhibits much hyped "exponential speed-up."

Meanwhile, read my paper which proves that quantum entanglement is not a fundamental feature of the world: Proposed Experiment and its Numerical Simulation.