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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

#71

Also of note is Gil Kalai's updated take on the experiment [1]. The heart of the complaint is that the quantum computer's solution to this problem relies on a calibration process, which is done on a classical computer and requires resources orders of magnitudes higher than the quantum portion of the computation: > The Google experiment actually showed that a quantum computer running for 100 seconds PLUS a classic com…

Even if the calibration process "cheats", why should we care? It's not like being practical is the goal. After the calibration is done, you still have a device that can do something believed intractable on classical computers. If it is possible for a classical computer to get comparable results just from a long calibration process, then that means the cross entropy test is flawed/limited, which is a separate argument.

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

#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 low-qubit circuits.

    The biggest gripe: basing the argument on what classical computers can’t do. Can’t is an assumption that’s been dis-proven about so many things so many times. Who knows what new algorithms people will come up with down the line doing what we previously couldn’t do. I want an argument that’s instead based on what can and has been done vs the new thing being done. I similarly preferred constructivist logic to classical since the latter was assuming things didn’t exist. Universe surprises me too often for that stance.
Another thing about these is the comparison to supercomputers. Me personally, I don’t care if the quantum computer outperforms supercomputers. I’m looking at practical QC like anything else: does it do the job more cost-effectively than alternative solutions? That cost includes hardware, any leasing/licensing, maintenance, specialists, etc. If it does, then they’ve achieved something for me. If it doesn’t, then QC was an implementation detail for a system that didn’t make the cut.

FPGA’s are already an example of how this might play out. They’re friggin amazing with all kinds of potential. I’d love to have a desktop loaded with them with libraries using them to accelerate my apps. Them being invented and improved wasn’t enough for that, though. The duopoly, esp supported by patents, has kept prices of high-performance FPGA’s way too high.

It would be better if they were priced more like flash memory with the synthesis software being more like mass-market A/V software. We’d see an explosion of use. Instead, the legal system allowed the inventors to keep competition and innovation at low levels to maximize profit. I expect the same with practical QC for at least 20 years. I’ll still be using a mix of NUMA, GPU’s and FPGA’s while early adopters mess around with quantum computers.

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

#73

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.

Such a demonstration would prove nothing of importance, partly because the issue is not how fast a particular run takes, but how running time grows with the size of the problem. More significantly, the issue is whether the paper's argument for its original claim is sound, and that would be best addressed by showing where it goes wrong. For a brief and clear explanation, read this excellent post: https://news.ycombina…

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.

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

#74
post #8

The main takeaway here is figure 1 in this article: they show that for an increasing circuit depth, computation time (on a classical computer) scales linearly. Google claims, on the other hand, that a classical calculation would scale exponentially. This is the basis for the graph in the Google blog [1], which seems to suggest that the Quantum computer can easily reach points (such as qbits=50, cycles=25) which the c…

There are many problems where the best known quantum algorithm is asymptotically better than the best known classical algorithm but, as far as I've heard, nobody has ever found a case where the best quantum algorithm can be proved to be better than the best classical algorithm. So there's always going to be a danger of this happening no matter what problem you attack.

There are provable quadratic speedups over all possible classical algorithms.

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

#75
IBM's head of research had a pretty confident statement the other day: "I’m convinced there are more quantum computers working here than the rest of the world combined, in this building," Dr. Gil said.

[1]https://www.nytimes.com/2019/10/21/science/quantum-computer-...

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

#76

Also of note is Gil Kalai's updated take on the experiment [1]. The heart of the complaint is that the quantum computer's solution to this problem relies on a calibration process, which is done on a classical computer and requires resources orders of magnitudes higher than the quantum portion of the computation: > The Google experiment actually showed that a quantum computer running for 100 seconds PLUS a classic com…

Even if the calibration process "cheats", why should we care? It's not like being practical is the goal. After the calibration is done, you still have a device that can do something believed intractable on classical computers. If it is possible for a classical computer to get comparable results just from a long calibration process, then that means the cross entropy test is flawed/limited, which is a separate argument…

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"!

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

#77
post #49

Earlier quoted context omitted.

Supremacy does not mean simply faster. That is already proven. It means impossible to do on a classical computer.

I'm sure you mean infeasible. "Impossible" goes back to a problem's decidability. If a problem is undecidable, there's no way you're going to find its solution by switching computational models; classical computers can do anything a quantum computer can do, just "slower".

Not if they use up all the energy in the visible universe or they need so much power they collapse and form a black hole.

Real quantum computers should be able to do calculations that are that powerful, assuming we can prove the best classical algorithms are really exponential.

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

#78

Also of note is Gil Kalai's updated take on the experiment [1]. The heart of the complaint is that the quantum computer's solution to this problem relies on a calibration process, which is done on a classical computer and requires resources orders of magnitudes higher than the quantum portion of the computation: > The Google experiment actually showed that a quantum computer running for 100 seconds PLUS a classic com…

Even if the calibration process "cheats", why should we care? It's not like being practical is the goal. After the calibration is done, you still have a device that can do something believed intractable on classical computers. If it is possible for a classical computer to get comparable results just from a long calibration process, then that means the cross entropy test is flawed/limited, which is a separate argument…

At issue, as I understand it, is whether the results from the 53-bit simulation (which would take 10,000 years, or 2.5 days, depending on who you believe) are valid or whether they are just so much junk because they haven't been calibrated and rely on calibrations that may or may not generalize. Kalai responds to Peter Shor making similar critiques in the comment threads in the blog, but it seems it comes down to clarifications on methodology, so may not be a fatal defect.

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

#80

Earlier quoted context omitted.

There are many problems where the best known quantum algorithm is asymptotically better than the best known classical algorithm but, as far as I've heard, nobody has ever found a case where the best quantum algorithm can be proved to be better than the best classical algorithm. So there's always going to be a danger of this happening no matter what problem you attack.

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.
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