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D-Wave's advancements are very interesting to me for a few reasons. The first is that initially many people suspected D-Wave was a scam, because the most succe

D-Wave's advancements are very interesting to me for a few reasons. The first is that initially many people suspected D-Wave was a scam, because the most successful research efforts in quantum computing used just a few qubits, and D-Wave claimed a massive improvement (something like 128 or 256). Scott Aaronson (http://www.scottaaronson.com http://www.scottaaronson.com) was perhaps the most vocal critic. Over the years, the criticism has softened, and D-Wave has managed to get a paper or two into Nature. I think the truth of what they've achieved is somewhat less than what their marketing machine would like to suggest, but it's nevertheless very impressive (and D-Wave is certainly a place I'd like to work at if I could). To clarify, D-Wave has not developed a general-purpose quantum computer, and in fact the term "general purpose" is kind of ill-defined for quantum computing anyway. Right now, there are a lot of different quantum effects that are used in different ways to accomplish specific tasks. I believe D-Wave's device uses quantum annealing to solve certain optimization problems, but someone check me if I'm wrong. The little I do know about quantum computing relates to my area of study: simulation. The computation required to exactly solve the Schrodinger equation scales with 2^N for the number of particles (or whatever basis the equation is set in). Even the largest supercomputers are incapable of doing more than a few atoms [which, incidentally, is actually what I'm attempting to accomplish right now for a project that I should be working on instead of posting on here...] Anyway, with quantum computers, the scale would be O(N) instead of O(2^N), so you could perform incredibly accurate simulations that reach chemical accuracy. Chemical accuracy is kind of the holy grail of simulation, because what it means is that you can predict actual, macroscopic chemical properties of a variety of substances without doing any real-world experiments whatsoever. I believe it has been accomplished for things like pure hydrogen and quite a few bosonic systems (bosons are easier to simulate since they don't suffer from the fermion sign problem - http://en.wikipedia.org/wiki/Numerical_sign_problem http://en.wikipedia.org/wiki/Numerical_sign_problem). Anyway, I probably sound like I know more than I really do, but hopefully this gives you an idea of what kind of applications a real, working quantum computer could be used to achieve.

papaf 14y ago
Out of interest, when the chemically accurate simulations are made are there any surprises? Or do the estimations that are normally used good enough for most purposes?
- escherba 14y ago
  I'm not an expert on Comp Chem, but you might want to rephrase your question. If the simulation is "chemically accurate", of course it will match the real-world, by definition of "accurate"...
  - papaf 14y ago
    My understanding of these things is that the dynamics of the real world are not easily measurable at this scale. An alternative is to simulate using using packages such as Gromacs: http://www.gromacs.org/About_Gromacs These packages are truly incredible but use relatively crude approximations and are in wide use. It is possible to get a decent paper out that uses a simulation as evidence to support an idea. The aim of my question was to see if chemically accurate simulations come up with significantly different answers or to see if the current way of doing things is a good enough approximation.
    - hagy 14y ago
      You bring up an excellent point, papaf. The accuracy of the empirical force fields used in molecular dynamics simulation engines (such as Gromacs) is a hotly debated topic. Even without quantum computing the issue can be addressed with conventional computers that perform quantum mechanical calculations on interacting molecular fragments. The forces calculated from quantum mechanics can then be compared with those calculated from molecular dynamics force fields (as an example see Sherrill et al. http://onlinelibrary.wiley.com/doi/10.1002/jcc.21226/full http://onlinelibrary.wiley.com/doi/10.1002/jcc.21226/full ). Such studied have shown that current force fields fail to model certain chemical interactions and need improved. Specifically, the underlying functional forms used to model molecular forces need revised. Currently such investigations are limited in scope by the large computational resources required to perform a single quantum mechanical calculation on a molecular fragment. With quantum computers, tens of thousands of such calculations could be performed and the results could be used to optimize new molecular force fields through multivariate regression.
      - Xcelerate 14y ago
alan_cx 14y ago
Disclaimer: I have no idea what I'm talking about in this area. So I reserve the right to dumb questions!!! Is it possible that in the future rather than having a sort of general "quantum computer", something like quantum processors will be built for specific computing tasks? Each very different in config and unique, specifically designed and used for one thing and one thing only?
- asafira 14y ago
  Sure it's possible, and that's probably what will happen with the first few quantum computers. =D
greenmountin 14y ago
People keep referring to Scott Aaronson like he changed his mind, and it's pretty clear he didn't. He just didn't want to be the Chief Naysayer anymore; he has more important things to do and frankly that shouldn't be his calling card. I think the only part of "general-purpose quantum computer" D-Wave can claim is the "computer" part. They have not proven that any part of their annealing is "quantum". They have pretty epic lithography/fabrication skills, and are barreling ahead without any regard for coherence. They also have just an insane number of control lines, so there's some innovation there. But their net worth becomes negative if you count the bad press for quantum computing in having a charlatan claim they have 1024 qubits and are "500,000" times faster at solving Sudoku. Other fields are having this PR problem too, where even careful program reviews are getting brutalized by the PR news cycle (see recent dark-matter experiment: http://profmattstrassler.com/2013/04/03/ams-presents-some-first-results/ http://profmattstrassler.com/2013/04/03/ams-presents-some-fi... -- forgive the typography)

papaf 14y ago

Out of interest, when the chemically accurate simulations are made are there any surprises? Or do the estimations that are normally used good enough for most purposes?

escherba 14y ago
I'm not an expert on Comp Chem, but you might want to rephrase your question. If the simulation is "chemically accurate", of course it will match the real-world, by definition of "accurate"...
- papaf 14y ago
  My understanding of these things is that the dynamics of the real world are not easily measurable at this scale. An alternative is to simulate using using packages such as Gromacs: http://www.gromacs.org/About_Gromacs These packages are truly incredible but use relatively crude approximations and are in wide use. It is possible to get a decent paper out that uses a simulation as evidence to support an idea. The aim of my question was to see if chemically accurate simulations come up with significantly different answers or to see if the current way of doing things is a good enough approximation.
  - hagy 14y ago
    You bring up an excellent point, papaf. The accuracy of the empirical force fields used in molecular dynamics simulation engines (such as Gromacs) is a hotly debated topic. Even without quantum computing the issue can be addressed with conventional computers that perform quantum mechanical calculations on interacting molecular fragments. The forces calculated from quantum mechanics can then be compared with those calculated from molecular dynamics force fields (as an example see Sherrill et al. http://onlinelibrary.wiley.com/doi/10.1002/jcc.21226/full http://onlinelibrary.wiley.com/doi/10.1002/jcc.21226/full ). Such studied have shown that current force fields fail to model certain chemical interactions and need improved. Specifically, the underlying functional forms used to model molecular forces need revised. Currently such investigations are limited in scope by the large computational resources required to perform a single quantum mechanical calculation on a molecular fragment. With quantum computers, tens of thousands of such calculations could be performed and the results could be used to optimize new molecular force fields through multivariate regression.
    - Xcelerate 14y ago

alan_cx 14y ago

Disclaimer: I have no idea what I'm talking about in this area. So I reserve the right to dumb questions!!! Is it possible that in the future rather than having a sort of general "quantum computer", something like quantum processors will be built for specific computing tasks? Each very different in config and unique, specifically designed and used for one thing and one thing only?

asafira 14y ago
Sure it's possible, and that's probably what will happen with the first few quantum computers. =D

greenmountin 14y ago

People keep referring to Scott Aaronson like he changed his mind, and it's pretty clear he didn't. He just didn't want to be the Chief Naysayer anymore; he has more important things to do and frankly that shouldn't be his calling card. I think the only part of "general-purpose quantum computer" D-Wave can claim is the "computer" part. They have not proven that any part of their annealing is "quantum". They have pretty epic lithography/fabrication skills, and are barreling ahead without any regard for coherence. They also have just an insane number of control lines, so there's some innovation there. But their net worth becomes negative if you count the bad press for quantum computing in having a charlatan claim they have 1024 qubits and are "500,000" times faster at solving Sudoku. Other fields are having this PR problem too, where even careful program reviews are getting brutalized by the PR news cycle (see recent dark-matter experiment: http://profmattstrassler.com/2013/04/03/ams-presents-some-first-results/ http://profmattstrassler.com/2013/04/03/ams-presents-some-fi... -- forgive the typography)