[HN Gopher] Grid of atoms is both a quantum computer and an opti...
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Grid of atoms is both a quantum computer and an optimization solver
Author : isaacfrond
Score : 52 points
Date : 2023-02-16 12:56 UTC (10 hours ago)
(HTM) web link (arstechnica.com)
(TXT) w3m dump (arstechnica.com)
| Gravityloss wrote:
| If we want to simulate molecular systems that have quantum
| effects, with a quantum computer, is it a good fit?
|
| Say we want to create designer molecules for flow batteries. A
| few benzene rings and some "arms" with a few carbons and hydroxyl
| group at the end. The potential design space is absolutely
| humongous. Can a quantum computer simulate something like that
| relatively directly, and then see how that reacts in various
| situations, oxidizing and reducing? If you have a system with 20
| atoms, how many qubits would you need, and so on?
|
| Right now researchers make a best guess, then synthesize the
| material. That can take months. Then they make experiments, and
| usually there are some surprises. Machine learning has been
| proposed to help but probably has limitations...
| jlokier wrote:
| Little known fact: Simulating quantum physical systems was the
| original motivation for building quantum computers, because
| those simulations are infeasible without one, and someone
| figured out it would be, in principle, feasible to run those
| simulations using a computer based on quantum effects.
|
| There's a neat symmetry to it. We can't be certain quantum
| computers work at useful scales, until we've built one, because
| there's no feasible way to simulate the physics of a useful
| size quantum computer without using one.
| jacobr1 wrote:
| > there's no feasible way to simulate the physics of a useful
| size quantum computer without using one.
|
| What do the diverging growth curves look like? We probably
| could brute force simulate the exponential states within a
| small-n using conventional computing, just by paying for more
| parallelism and time. At some point that doesn't scale (more
| computers needed than atoms on earth, for longer than the
| heat-death of the universe or whatever) but surely there are
| interesting problems we can model before whatever inflection
| point exists? If so - what kind of scale is that?
| ta988 wrote:
| In theory yes, but we can't get one with enough qbits (you
| would need more qbits than your molecule because you need to
| encode positions and interactions of electrons at the very
| least), enough configurability (current q-computers are
| somewhat limited to which qbit can interact with which through
| which mean) and that is able to keep decoherence away (which
| limits how much it can scale).
|
| It seems that we are really hitting a wall every time we want
| to scale them to a useful size and keep the number of possible
| interactions between qbits high and noise/decoherence level
| low.
|
| So for now we don't have the technology (if ever), it is not
| just a problem of "just scaling by adding more qbits" we need a
| new approach.
| [deleted]
| whitten wrote:
| So you can make a grid with less than 40 quantum atom pairs, each
| of which is coupled in some way to another atom, and since
| measuring one atom guarantees the other atom is in the opposite
| state, you can bypass Heisenberg uncertainty.
|
| But wait. To solve an NP problem of size n, you need square(n)
| atoms. But 40 atoms is barely more than 36, so you can solve a NP
| problem of size 6, which is easy and possible.
|
| I think brute force on an NP problem is factorial(n) So
| factorial(6) == 6 ! == 6 * 5 * 4 * 3 * 2 * 1 == 720.
|
| Am I misunderstanding something here ?
| karmakaze wrote:
| The other atom is not in the 'opposite state' for all
| properties, rather it has one property which is entangled so
| whatever accuracy you just measured, you know to the same
| accuracy of the other in the entangled property only.
|
| Also 40 bits in superposition can represent 2^40 possibilities.
| petters wrote:
| > I think brute force on an NP problem is factorial(n)
|
| No, NP [?] EXPTIME, which means that exponential time should be
| enough.
| amrb wrote:
| Still find it nuts you need to operate the system at 0 kelvin. I
| assume if we had super efficient cooling equipment (not LN2) we
| could also do superconductors on a small scale?
| ta988 wrote:
| LN2 is not enough you need LHe for most superconductors. It is
| usually cooled by LHe that is itself shieled by LN2 to limit
| losses.
|
| LN2 is relatively cheap not LHe.
|
| That's why there are recylcing systems to recover the boiling
| off He in MRIs, NMRs and other supraconducting systems.
|
| There are systems that allow cooling without wasting LHe/LN2
| but they are pretty limited in size or costly:
|
| https://hexus.net/tech/news/cooling/131414-worlds-first-abso...
|
| https://www.wired.co.uk/article/mri-magnet-cooling
|
| https://en.wikipedia.org/wiki/Dilution_refrigerator
|
| edit: s/LH2/LHe
| carterschonwald wrote:
| Liquid He right? Liquid hydrogen is relatively cheap
| ta988 wrote:
| Thanks will edit
| phonebucket wrote:
| > Still find it nuts you need to operate the system at 0
| kelvin. I assume if we had super efficient cooling equipment
| (not LN2) we could also do superconductors on a small scale?
|
| Neutral atom quantum computers (the type outlined in the
| article) work at room temperature.
|
| Superconducting qubit based quantum computers do indeed require
| cooling to these levels, though.
| packetlost wrote:
| You use lasers to optically trap and cool the atoms, you can
| get them insanely cold very reliably with methods like this:
|
| https://en.wikipedia.org/wiki/Optical_molasses
|
| https://en.wikipedia.org/wiki/Polarization_gradient_cooling
|
| https://en.wikipedia.org/wiki/Doppler_cooling
|
| The components in a system like this are probably operating at
| room temperature.
| cwillu wrote:
| Smells like d-wave nonsense.
|
| <finishes reading>
|
| Yeah, it's the same nonsense.
|
| Reminder: quantum computing is not expected to be able to improve
| the solutions of NP-complete problems by more than a quadratic
| factor, unless some commonly accepted conjectures can be proven
| false. If that happens, you'll be hearing about it from more than
| just a analog computer company's marketing materials.
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