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> With quantum computing there are also no real signs that a quantum computer will beat a "classical" computer at anything any time soon. It always was and stil

by wolfgke 10y ago

> With quantum computing there are also no real signs that a quantum computer will beat a "classical" computer at anything any time soon. It always was and still is very difficult to get quantum systems to scale and you need a large enough system to make a difference and it may be impossible to do so. Again a lot of this is more of an engineering problem though admittedly the line between physics and engineering can be blurry since it's not always clear whether something can't be done because you've reached a fundamental limitation vs. having a clever enough design. The mentioning of quantum computers is very interesting in the following sense: If one were able to build a sufficiently large quantum computer, this would provide strong evidence that the (at the moment rather hypothetical) theory whether quantum mechanics is rather an emergent phenomen by a deterministic process (cellular automaton) > https://arxiv.org/abs/1405.1548 https://arxiv.org/abs/1405.1548 which the Nobel laureate Gerard 't Hooft worked on for the last years is probably wrong. To quote p. 79-80: "Such scaled classical computers can of course not be built, so that this quantum computer will still be allowed to perform computational miracles, but factoring a number with millions of digits into its prime factors will not be possible – unless fundamentally improved classical algorithms turn out to exist. If engineers ever succeed in making such quantum computers, it seems to me that the CAT is falsified; no classical theory can explain quantum mechanics." On the other hand, if we seriously get into trouble building a sufficiently large quantum computer (despite our best efforts), this would at least to me provide evidence that 't Hooft is on something - since that this is a prediction that his Cellular Automaton Interpretation of Quantum Mechanics provides.

sgt101 10y ago
I think that the largest simulation of a quantum computer on a super computer is about 40qbits. Therefore quantum supremacy (weak...) is 41 stable qbits. There are numbers of groups out there that are building (working on projects with the funding to complete) machines with 100's of stable qbits now, so my argument is that quantum supremacy of the weak sort is a matter of engineering. I think that quantum computers that factor primes with 100's of digits (like 2048 bit ones) requires 1000's of qbits, say a couple of orders of magnitudes beyond the machines that are currently in train to be built. The Hooft thing is that there are limits on computation due to the process of the universe and that if a classical computer that was at the plank scale, runs at plankian speed (help help I am using terms I can't understand!!!) and covered the whole of the universe couldn't do it from the beginning of time to heat death... then nor can an arbitrary QC. Shores algorithm does factors in (log n)^3 maybe we'll find that there are physical limits on the scale of QC which hold it below hundreds of millions of qbits where a plankian computer could be synthesised, and/or it may be that such a computer can't run at high clock speeds, and because of this BQP algorithms can't be run on problems that are not allowed in the sense that they somehow solve the universe. I don't think anyone has any reason to believe this is true in an engineering sense but there is every reason to believe that large QC will be very, very difficult in an engineering sense and I think that the people building one do expect to run into problems of this sort eventually, but at the moment they are delighted to find that they are able to do things at the lower end that will create devices that are going to be transformational for reasoning about some components of the physical universe - for example simulation of the interactions of very large molecules - maybe mapping seconds of a virus interacting with a cell membrane using months of QC ?
deleted 10y ago
[deleted]

by wolfgke 10y ago

sgt101 10y ago

I think that the largest simulation of a quantum computer on a super computer is about 40qbits. Therefore quantum supremacy (weak...) is 41 stable qbits. There are numbers of groups out there that are building (working on projects with the funding to complete) machines with 100's of stable qbits now, so my argument is that quantum supremacy of the weak sort is a matter of engineering. I think that quantum computers that factor primes with 100's of digits (like 2048 bit ones) requires 1000's of qbits, say a couple of orders of magnitudes beyond the machines that are currently in train to be built. The Hooft thing is that there are limits on computation due to the process of the universe and that if a classical computer that was at the plank scale, runs at plankian speed (help help I am using terms I can't understand!!!) and covered the whole of the universe couldn't do it from the beginning of time to heat death... then nor can an arbitrary QC. Shores algorithm does factors in (log n)^3 maybe we'll find that there are physical limits on the scale of QC which hold it below hundreds of millions of qbits where a plankian computer could be synthesised, and/or it may be that such a computer can't run at high clock speeds, and because of this BQP algorithms can't be run on problems that are not allowed in the sense that they somehow solve the universe. I don't think anyone has any reason to believe this is true in an engineering sense but there is every reason to believe that large QC will be very, very difficult in an engineering sense and I think that the people building one do expect to run into problems of this sort eventually, but at the moment they are delighted to find that they are able to do things at the lower end that will create devices that are going to be transformational for reasoning about some components of the physical universe - for example simulation of the interactions of very large molecules - maybe mapping seconds of a virus interacting with a cell membrane using months of QC ?

deleted 10y ago

[deleted]