[Xcelerate]

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) 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).

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.

[greenmountin]

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-fi... -- forgive the typography)

[alan_cx]

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]

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

[papaf]

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?

[asafira]

D.E. Shaw current is one of the leaders (if not the leader) in molecular dynamics (i.e., studying the motion of the specific atoms in a molecule, or watching the dynamics of a chemical reaction), and it's a really hard problem. Roughly speaking, you have to calculate a constant (but also fairly large) number of operations to calculate the configuration of the molecule(s) for every _femtosecond_ of time. It would be great to see things happen at a tens of microseconds, but that is a LOT of computation.

This is useful becaue it would mean that we could see exactly how reactions take place and perhaps even engineer interesting chemical/biological phenomena. Certain processes in your body depend on proteins moving certain substances or reacting in certain ways, and if we can simulate all that with a computer, we can start to build chemical/biological tools for, for example, fighting certain diseases

[adrianhoward]

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?

Well - it's more that there are entire classes of things that we can't simulate in any reasonable amount of time that (in theory) QCs should be very good at.

Protein folding for example. Finding the lowest energy state that protein's fold into is really, really hard and slow. QCs can theoretically do it very, very quickly. This opens up whole areas of experimentation and validation that are closed to us at the moment because the feedback cycle on solutions is so darn slow and/or inaccurate.

Protein folding errors are at the heart of diseases like Alzheimer’s, Huntington’s and Parkinsons. QCs capable of simulating the chemistry involved would be a huge help in attacking those problems.

[escherba]

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]

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]

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 ). 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]

Nice to see another GT person on HN! (Did my undergrad there.) Have you worked with Dr. Sherrill? It's funny you mention him; I was actually reading one of his presentations on electron-electron correlation last night.

[hagy]

Cool. I'm a grad student in another chemistry theory group. Dr. Sherrill definitely has the best notes on electronic structure calculations.