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Quantum computers: amazing progress, but probably false supremacy claims

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Re: Quantum computers: amazing progress, but probably false supremacy claims

#71

Post by sriku »

Nokinside wrote: post #49
sriku wrote: post #43

I've had my eyes on Adrian Thompson's genetically evolved FPGA circuits for a while now - they do amazing things very economically and exploit analog circuit properties. So I've always wondered what if we make unreliable but super tiny atomic level programmable gates where we know the unreliability stems from quantum fluctuations, and then evolve circuits over millions of generations (A.T. ran thousands) to see if th…

'Quantum effects' are already exploited in analog components. TFET's work by modulating quantum tunneling. Zener reverse breakdown in Zener diode is also quantum effect. Esaki diode uses quantum effects. Unfortunately just because the single component relies on quantum effects does not have anything to do with quantum speedup in computation. Quantum computation exploits entanglement in larger scale than normal. The w…

Well, trivially that's a yes. However, the "specification level breach" property of A.T.'s work is what intrigued me - i.e. the circuits are specified to do a digital task, but work in an analog manner - constructing antennas and receivers - to the extent that the same digital circuit wouldn't work when written to another FPGA.

Also, entanglement doesn't need to be perfect. You can have 1% entanglement too and have that propagate over time and operations. The question is whether an evolved circuit can figure out pathways to use that little bit of entanglement in ways that our understanding doesn't quite admit .. in much the same way as a digital FPGA designer wouldn't think about using not-gates as antennae.

An unreliable circuit achieved this way would also be interesting I think.

Re: Quantum computers: amazing progress, but probably false supremacy claims

#72

Post by sriku »

deepnotderp wrote: post #46
sriku wrote: post #43

I've had my eyes on Adrian Thompson's genetically evolved FPGA circuits for a while now - they do amazing things very economically and exploit analog circuit properties. So I've always wondered what if we make unreliable but super tiny atomic level programmable gates where we know the unreliability stems from quantum fluctuations, and then evolve circuits over millions of generations (A.T. ran thousands) to see if th…

The main problem is that errors accumulate and your circuits are extremely "anti-robust". If you put an antenna or something next to it there was a good chance it would stop working properly for example.

Most likely yes. But, as I noted in another comment, that would still be interesting since we can test for entanglement on a larger scale. I'm kind of expecting error correction to "evolve" in the iterations. Robustness can come later.

Re: Quantum computers: amazing progress, but probably false supremacy claims

#73

Post by deepnotderp »

sriku wrote: post #72
deepnotderp wrote: post #46

Earlier quoted context omitted.

The main problem is that errors accumulate and your circuits are extremely "anti-robust". If you put an antenna or something next to it there was a good chance it would stop working properly for example.

Most likely yes. But, as I noted in another comment, that would still be interesting since we can test for entanglement on a larger scale. I'm kind of expecting error correction to "evolve" in the iterations. Robustness can come later.

I've worked a decent bit with stochastic search (not necessarily just EAs/GAs but also Metropolis-Hastings and extensions of MH) and the search process tends to favor probabilistic and inaccurate individual units but gangs many of them together for reliability.

This is wholly different from how we view computer programs today. It may work, but you'd better have a good application in mind, otherwise you'll get laughed/shooted out of the room.

Re: Quantum computers: amazing progress, but probably false supremacy claims

#74

Post by GistNoesis »

chr1 wrote: post #70
GistNoesis wrote: post #61

Earlier quoted context omitted.

If your model can't predict its limits, it is an indication that you are already past its limits. When you build a model, you build it to map the range of behaviors you are interested in. When mathematical infinities of any kind (like infinite computational power) emerge it's usually a strong hint that the model is not applicable, not an invitation to fantasize about the things you will be able to achieve following y…

All the physical theories we had so far require infinite computational power, because they work with real numbers, it's easy to say that it is wrong, but that's not really useful without saying what is right. There are several interpretations of quantum mechanics that predict quantum computers not working in different ways, to find which one of them is correct you need an experiment that is not described by tradition…

Working with real numbers, doesn't mean requiring infinite computational power. Numerical integration can make the integration error arbitrary small, even without symplectic integrators, this mean you can work with finite-precision number instead.

The thing with building a quantum computer is that the original hard test (breaking RSA) is being watered down. Until you prove that you've done it you only get non-results telling you that you are not there yet but you don't know why and require ever more funds. So the incentives are badly aligned and you prove a softer test that you try to sell as something as good as the hard test. If you are not familiar with bias you might even fool yourself into thinking you are making progress because you managed to reach the softer goal you have set for yourself while you are adding complexity to obscure your theoretical shortcomings.

>Building quantum computers is the first experiment that has a chance to show what exactly is wrong with QM.

Don't blindly trust experiments : Bell officially proved that what's very probably wrong is right. Especially when they require expensive equipment or specialized knowledge to reproduce. If there is something wrong with the protocol you can easily falsely convince yourself. Putting a non-zero prior on unknowns unknowns should be a must.

If you ever try to question the Gospel of Non-Locality, you will find yourself cast aside like many before as the vast literature show.

Re: Quantum computers: amazing progress, but probably false supremacy claims

#75

Post by computerex »

lawrenceyan wrote: post #69
computerex wrote: post #68

Earlier quoted context omitted.

I think you have serious conceptual holes in your understanding of the post. > The issues that Kalai poses as to the validity of the experiments done by Google’s Quantum AI Lab is that the difference between the ideal distribution D and sampled distribution D’ is meaningfully different enough from each other, that significant results cannot be obtained from the experiment in comparing performance to classical simulat…

> By creating a 0-1 distribution we mean sampling sufficiently many times from that distribution D so it allows us to show that the sampled distribution is close enough to D. Because of the imperfection (noise) of qubits and gates (and perhaps some additional sources of noise) we actually do not sample from D but from another distribution D’. However if D’ is close enough to D, the conclusion that classical computers…

The passage you quoted is under the:

> Achieving quantum supremacy via sampling

Headline and is simply describing some technical details of the experiment. This is not the author bringing any points of contention, there is no disagreement here at all, this is merely defining the criteria for how quantum supremacy is defined.

I highlighted his points of contention as a response to your original comment that said he is nitpicking, here: https://news.ycombinator.com/item?id=21168813

His main point of contention seems to be:

They need to understand the D' distribution more by running the experiment on lower qubit configurations, comparing the experimentally sampled distributions with one another across qubit configurations and across multiple runs of the same qubit configurations. As it is, he says that they may not have even sampled from D'. The burden of proof is on the experimenters to quantitatively show that they did.

There were other issues raised, like Google not being quantitative enough with their claims of the gains achieved in their supremacy statement.

He also brings up a more general issue with quantum computing in correlated errors, which are described in more detail in his paper here: http://www.ma.huji.ac.il/~kalai/Qitamar.pdf

But it boils down to that qubit logic gates experience positively correlated errors, which unless corrected with quantum fault tolerance will have an impact on any result.

I hope this clears up some misconceptions. In general it is a good idea to use the principle of charity and try to address the best possible interpretation of someone's argument. This is true even more so when commenting on someone who is literally close to the top in their field.

Re: Quantum computers: amazing progress, but probably false supremacy claims

#76

Post by Nokinside »

sriku wrote: post #71
Nokinside wrote: post #49

Earlier quoted context omitted.

'Quantum effects' are already exploited in analog components. TFET's work by modulating quantum tunneling. Zener reverse breakdown in Zener diode is also quantum effect. Esaki diode uses quantum effects. Unfortunately just because the single component relies on quantum effects does not have anything to do with quantum speedup in computation. Quantum computation exploits entanglement in larger scale than normal. The w…

Well, trivially that's a yes. However, the "specification level breach" property of A.T.'s work is what intrigued me - i.e. the circuits are specified to do a digital task, but work in an analog manner - constructing antennas and receivers - to the extent that the same digital circuit wouldn't work when written to another FPGA. Also, entanglement doesn't need to be perfect. You can have 1% entanglement too and have t…

Entalgement is very fragile. You can't keep even "little bit" of entanglement in any normal temperature.
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