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Is it possible to massively speed up ray tracing by representing geometry in a quantum program and then using superposition to evaluate many ray paths simultane

Is it possible to massively speed up ray tracing by representing geometry in a quantum program and then using superposition to evaluate many ray paths simultaneously? That would be exciting in <N> years for real time accurate ray tracing. This is just a wild guess without much knowledge of quantum computing at all though.

grondilu 9y ago
Ray tracing is typically the kind of things you want to do as fast as possible, ideally in real time. Quantum computers will never work fast. Also if I'm not mistaken ray tracing scales well with conventional computers : the quality of your output is proportional to the number of rays you simulate. So it's not an appropriate use case for quantum computers.
- posterboy 9y ago
  but it's not linear with the number of reflections and transissions, I guess, if you want physically correct materials. Or if you want aberations and, well, "quantum effects" like in the slit experiment.
nhaehnle 9y ago
In short, no. Quantum computers don't really compute many things in parallel. Or rather, they do, but the problem is getting the results out. To stick with your ray tracing question, you could probably indeed trace an exponentially (in the size of the computer) number of rays, but at the end you have to do go back to the classical world to actually read out data, and you'd essentially be able to only read out the result of one ray picked at random. Quantum computers are only know to provide exponential speedups in cases where there is some algebraic structure to exploit when condensing the exponentially many computations down to a single result. That's why you can get an exponential speedup for factoring or discrete logarithm, but not for symmetric cryptography or really any other useful problem (except for the kind of circular problem of simulating quantum systems). That's what makes me personally hope that quantum computers will never scale. The likely outcome of quantum computing is the worst of all worlds: all known practically useful cryptography will be broken, and practically nothing will really benefit.
- OscarCunningham 9y ago
  >The likely outcome of quantum computing is the worst of all worlds: all known practically useful cryptography will be broken, and practically nothing will really benefit. I agree with you on the technical points, but I think this is a tad pessimistic. Firstly, by the time we have quantum computing we will probably also have quantum cryptography. Quantum cryptography is secure against quantum computers and is also vastly more simple than existing crypto (no complicated algorithms to mess up). So I expect cryptography to improve. Secondly, while quantum computers won't be useful for everything, they will have amazing applications. The "simulating quantum systems" thing will be hugely useful for studying chemistry. And Grover's algorithm will provide a significant speedup for a whole host of interesting problems, especially in machine learning.
  - Moodles 9y ago
    > Quantum cryptography is secure against quantum computers and is also vastly more simple than existing crypto (no complicated algorithms to mess up). Can you explain this statement? I understand that algorithms such as RSA might require particular padding or what have you to be secure in practice, but is quantum-resistant crypto much different?
    - charlieflowers 9y ago
      It's completely different. The underlying mechanism is the fact that observing the state on one member of an entangled pair changes the state of the other member.
      - OscarCunningham 9y ago
        More specifically, the important fact is that it's impossible for three particles to be (maximally) entangled simultaneously. So you can verify that no one eavesdropped when you agreed your one-time-pad.
        Kemschumam 9y ago
cottonseed 9y ago
No. That's a common misconception about how quantum computation works. Read this: https://www.smbc-comics.com/comic/the-talk-3 https://www.smbc-comics.com/comic/the-talk-3
panic 9y ago
SIGGRAPH 2016 had a paper about "quantum supersampling" which does something like that: https://vimeo.com/180284417 https://vimeo.com/180284417
- orbital-decay 9y ago
  I've enjoyed the talk up until the liquid helium part.

grondilu 9y ago

Ray tracing is typically the kind of things you want to do as fast as possible, ideally in real time. Quantum computers will never work fast. Also if I'm not mistaken ray tracing scales well with conventional computers : the quality of your output is proportional to the number of rays you simulate. So it's not an appropriate use case for quantum computers.

posterboy 9y ago
but it's not linear with the number of reflections and transissions, I guess, if you want physically correct materials. Or if you want aberations and, well, "quantum effects" like in the slit experiment.

nhaehnle 9y ago

In short, no. Quantum computers don't really compute many things in parallel. Or rather, they do, but the problem is getting the results out. To stick with your ray tracing question, you could probably indeed trace an exponentially (in the size of the computer) number of rays, but at the end you have to do go back to the classical world to actually read out data, and you'd essentially be able to only read out the result of one ray picked at random. Quantum computers are only know to provide exponential speedups in cases where there is some algebraic structure to exploit when condensing the exponentially many computations down to a single result. That's why you can get an exponential speedup for factoring or discrete logarithm, but not for symmetric cryptography or really any other useful problem (except for the kind of circular problem of simulating quantum systems). That's what makes me personally hope that quantum computers will never scale. The likely outcome of quantum computing is the worst of all worlds: all known practically useful cryptography will be broken, and practically nothing will really benefit.

OscarCunningham 9y ago
>The likely outcome of quantum computing is the worst of all worlds: all known practically useful cryptography will be broken, and practically nothing will really benefit. I agree with you on the technical points, but I think this is a tad pessimistic. Firstly, by the time we have quantum computing we will probably also have quantum cryptography. Quantum cryptography is secure against quantum computers and is also vastly more simple than existing crypto (no complicated algorithms to mess up). So I expect cryptography to improve. Secondly, while quantum computers won't be useful for everything, they will have amazing applications. The "simulating quantum systems" thing will be hugely useful for studying chemistry. And Grover's algorithm will provide a significant speedup for a whole host of interesting problems, especially in machine learning.
- Moodles 9y ago
  > Quantum cryptography is secure against quantum computers and is also vastly more simple than existing crypto (no complicated algorithms to mess up). Can you explain this statement? I understand that algorithms such as RSA might require particular padding or what have you to be secure in practice, but is quantum-resistant crypto much different?
  - charlieflowers 9y ago
    It's completely different. The underlying mechanism is the fact that observing the state on one member of an entangled pair changes the state of the other member.
    - OscarCunningham 9y ago
      More specifically, the important fact is that it's impossible for three particles to be (maximally) entangled simultaneously. So you can verify that no one eavesdropped when you agreed your one-time-pad.
      - Kemschumam 9y ago

cottonseed 9y ago

No. That's a common misconception about how quantum computation works. Read this: https://www.smbc-comics.com/comic/the-talk-3 https://www.smbc-comics.com/comic/the-talk-3

panic 9y ago

SIGGRAPH 2016 had a paper about "quantum supersampling" which does something like that: https://vimeo.com/180284417 https://vimeo.com/180284417

orbital-decay 9y ago
I've enjoyed the talk up until the liquid helium part.