throwawaymaths 3 days ago

is there any reasoning that for besides highly reductionistic and repetitive systems like crystals, quantum computing can compute quantum properties of molecules?

it seems to me "the quantum computer you seek" is the molecule + the medium (especially the medium) itself

1
rsfern 3 days ago

So first I think I might need to apologize for some jargon collision - my background is mostly material simulation, and when I say “quantum simulation” I mostly mean using classical algorithms to solve the quantum mechanical wave equation describing a material or molecule.

I don’t pretend to have any particularly deep insight into quantum algorithms for chemistry, but [0] is a really nice review. It seems like there are a lot of possibilities for simulating general molecular and materials systems on quantum computers. The holy grail would be solving the exact quantum mechanical wave equation in sub-exponential time and space complexity. I don’t know how feasible that is, but it seems like people are making progress using quantum algorithms to accelerate approximate quantum simulation [1].

Back to all-atom c. elegans: I think quantum computing is more about accurate and scalable electronic structure modeling, and simulating enormous systems like this will still require fitting classical (meaning electrons are implicit) force fields and running them at scale for the foreseeable future. A lot of this is space complexity - I’m not sure how a quantum computer could do atomic simulations with sublinear scaling of qubits in the number of atoms being simulated, and were in the very early days of scaling quantum computers up

0: https://arxiv.org/abs/1812.09976

1: https://arxiv.org/abs/2307.07067

throwawaymaths 3 days ago

thanks for the reference.

yes. you nailed my point-that you will have to fit classical or quasi-classical fields, which is liable to require scads of qbits just to get close. qbits are just not "designed" to do that sort of thing.

in any case we ~solved protein folding heuristically and not using fields so i shouldn't be too pessimistic that it's impossible that quantum compute will help eventually.