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IBM casts doubt on Google's claims of quantum supremacy

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Re: IBM casts doubt on Google's claims of quantum supremacy

#91

Post by sanxiyn »

nickpsecurity wrote: post #72

I’m with them. My two problems when reading the original argument: They rigged the benchmark to be something quantum-specific before saying classical computers couldn’t do it. I get why. I’d just rather it be something they both could do, classical having great algorithms, and quantum one outperforms it many-fold. An old example was factoring. I’m sure there’s other examples out there. Maybe try to simplify them for…

Your biggest gripe can't be solved. P vs PSPACE is a great unsolved problem in computer science (almost as big as P vs NP), and since PSPACE can simulate quantum computer, any solution to your gripe immediately leads to resolution of P vs PSPACE.

Re: IBM casts doubt on Google's claims of quantum supremacy

#92

Post by lisper »

dooglius wrote: post #88
lisper wrote: post #83

Earlier quoted context omitted.

I can pre-calculate as many samples from the distribution as you can generate during the coherence time of the QC. Once you lose coherence, you have to re-calibrate, and during that time I can pre-compute another set of samples.

That's true, if you pre-sample you can beat the test. Is that the effect you think the calibration is having? > Once you lose coherence, you have to re-calibrate I didn't realize this, where did you see that?

> Is that the effect you think the calibration is having?

I have no idea. All I know (or at least I'm pretty sure of) is that you have to re-calibrate every time you lose coherence, otherwise it would not be calibration, it would be a one-time process that would be considered part of the construction of the QC.

> where did you see that?

Nowhere. I inferred it. It's possible that I'm wrong, but I'll give you long odds against. I have a pretty good understanding of how QCs work.

Re: IBM casts doubt on Google's claims of quantum supremacy

#93

Post by ehsankia »

hktuotroi wrote: post #40
mellosouls wrote: post #21

Repeating my question from the other thread: If IBM can cast doubt by describing a 2.5 day classical run, why not just do that instead, and blow the claim out of the water? There were a couple of responses (thanks) but I still don't understand - it looks like it's not as easy as they imply.

They didn't say 2.5 days on a laptop. They probably mean on a bunch of datacenters together. That is expensive. Google implied their supremacy over all of the world computers combined together.

These calculations of 2.5 day and 1000 years, they're calculations based on specific parameters, right? Could they just prove it on a smaller version of the problem instead? Can they do a version of the problem which takes maybe 1m on with IBMs algorithm and 1 year with Google's?

Re: IBM casts doubt on Google's claims of quantum supremacy

#94

Post by mellosouls »

mannykannot wrote: post #90
mellosouls wrote: post #73

Earlier quoted context omitted.

I'm sure you didn't intend snark, but no need for the tone - that's a new post and not a response to my original question. Thank you for the link to a potential explanation.

My apologies for the tone. I should have said that the best route to understanding the issue is probably via the linked post - it worked for me.

Thanks no worries

Re: IBM casts doubt on Google's claims of quantum supremacy

#95

Post by floren »

mellosouls wrote: post #21

Repeating my question from the other thread: If IBM can cast doubt by describing a 2.5 day classical run, why not just do that instead, and blow the claim out of the water? There were a couple of responses (thanks) but I still don't understand - it looks like it's not as easy as they imply.

The 2.5 day run is for Summit, the world's #1 supercomputer, owned by Oak Ridge National Laboratory. Getting use of the entire machine for 2.5 days may take some doing.

Re: IBM casts doubt on Google's claims of quantum supremacy

#96

Post by snops »

The linked paper shows the "classical system" is the Summit supercomputer[1], using 128 petabytes of disk. Still, its remarkable that the choice of a different simulation algorithm by IBM that trades memory for CPU usage cuts the time from 10,000 years to only 2.5 days.

[1] https://www.olcf.ornl.gov/olcf-resources/compute-systems/sum...

Re: IBM casts doubt on Google's claims of quantum supremacy

#97

Post by Barrin92 »

dooglius wrote: post #82
lisper wrote: post #76

Earlier quoted context omitted.

If you're going to allow cheating on calibration then it's trivial to achieve "quantum supremacy": simply precompute the answer and call that "calibration"!

There's no "answer" to precalculate, it's drawing from a distribution. Could you calibrate a non-quantum circuit to have a distribution passing the test? Supposedly, this is not possible even given arbitrary pre-computation time.

You can bring the complexity on a classical machine down to linear by allowing for large disk space, that is precisely the claim that IBM makes in response to the argument.

Re: IBM casts doubt on Google's claims of quantum supremacy

#99

Post by knzhou »

Following the quantum supremacy controversy is very frustrating. It gets constantly framed as a decisive step that changes everything, which is wrong. But then there's also an opposite and equally wrong reaction that any challenges to the claim prove that quantum computing doesn't work at all.

The reality is that quantum computing technology has been improving at the same steady pace for decades, and quantum supremacy was recently invented as a concrete but not very useful goal that people could realistically aim for in the near term. That is a totally standard and legitimate way of guiding technological progress.

The problem is that quantum supremacy is vaguely defined (what does "infeasible on any classical computer" mean? what computers can you use, and for how long?) but it is presented to the public as a sharp boundary -- which means that every company in the field has a huge incentive to claim they are the first. This IBM claim is not a fundamental objection. Given that everything they say is correct, Google could still achieve quantum supremacy by their standards just by incremental improvement, slapping a few more qubits on. So why even bother disputing Google's claim? Because it will set them back a few years, and that's enough time for IBM to make a claim of its own. That's why academics, who have no stake in what company gets the hype, will just consider this whole episode rather distasteful.

Re: IBM casts doubt on Google's claims of quantum supremacy

#100

Post by jessriedel »

atq2119 wrote: post #80
jessriedel wrote: post #74

Earlier quoted context omitted.

There are provable quadratic speedups over all possible classical algorithms.

Those are all about problems started in terms of querying some blackbox oracle. Whether the speedup holds up with a concrete instantiation of the blackbox is unknown.

Could you elaborate? You can search for the solution to any computational problem for which there is a binary function f(n) mapping candidates n to {0,1}, depending on whether it's a solution. Here, f is the "oracle", but it's only playing the role of representing the problem you're trying to solve, and I believe an f exists for all problems in NP.

If your set of solutions has N candidates, this requires only O(sqrt(N)) evaluations rather than O(N). If that function takes exponential time, then there is still of course no polynomial-time solution, but the quadratic speedup holds.

https://quantumcomputing.stackexchange.com/questions/2166/gr...

There are some NP problems for which we know techniques that are faster than brute-force search, but even then we can generally speed up those techniques in the same way.

https://link.springer.com/chapter/10.1007/978-3-540-78773-0_...

(I guess you could worry that for every problem there is an unknown techniques for classically speeding things up over brute-force search, but I thought this was known to be false, and in any case is unrelated to your point. I'm not an expert though.)

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