Quantum computers: amazing progress, but probably false supremacy claims

I couldn't disagree with you more.

The "author" you are referring to is: https://en.wikipedia.org/wiki/Gil_Kalai

He is a multi-award winner, internationally recognized researcher with several dozen publications on mathematics and computer science.

> The author raises points in contention, but they largely just seem like nitpicks to me.

I am not sure if you and I read the same post if you think that his points of contention are merely "nitpicks".

https://gilkalai.wordpress.com/2019/08/21/the-argument-again... https://gilkalai.files.wordpress.com/2019/09/main-pr.pdf https://arxiv.org/abs/1908.02499 https://gilkalai.files.wordpress.com/2019/09/cern.pptx

In the paper linked by this post, the author first very precisely defines how quantum supremacy is defined:

> if you can show that D’ is close enough to D before you reach the supremacy regime, and you can carry out the sampling in the supremacy regime then this gives you good reason to think that your experiments in the supremacy regime demonstrate “quantum supremacy”.

Author references an older paper running this experiment, brings up a very good point that there is no quantitative measurement provided of the similarity of D and D':

> The Google group itself ran this experiment for 9 qubits in 2017. One concern I have with this experiment is that I did not see quantitative data indicating how close D’ is to D.

First point of contention, doesn't seem like merely a "nitpick" and if you disagree I'd love to hear your reasoning.

> The twist in Google’s approach is that they try to compute D’ based mainly on the 1-qubit and 2-qubit (and readout errors) errors and then run an experiment on 53 qubits where they can neither compute D nor verify that they sample from D’. In fact they sample 10^7 samples from 0-1 strings of length 53 so this is probably much too sparse to distinguish between D and the uniform distribution

If they aren't sampling from D', then they can't compare it to D, and so this violates the basic definition of quantum supremacy via sampling of random circuits. The author's point about sample size being too sparse to compute the difference between D and the uniform distribution is also valid.

He made this caveat at the start

> A single run of the quantum computer gives you only one sample from D’ so to get a meaningful description of the target distribution you need to have many samples.

> What is needed is experiments to understand probability distributions obtained by pseudorandom circuits on 9-, 15-, 20-, 25- qubits. How close they are to the ideal distribution D and how robust they are (namely, what is the gap between experimental distributions for two samples obtained by two runs of the experiment.)

Seems like a big oversight to not do multiple runs and to compare the sampled D' distributions.

Scott Aaronson's description of the result made it out to be more subtle. If I understood it properly, it might be more like the kid shooting 20 arrows, which all form a particular pattern around a point that the kid can't choose or control at all. Now a regular archer can readily choose a particular point, in a way that the kid can't, but can't produce the sort of pattern that the kid does with nearly as much accuracy and nearly as little effort.

Or to make a less specific analogy, there is something about the kid's archery that regular archers can't replicate with their archery skills, but it's not really something that anyone would traditionally have described as "skilled archery". Then Aaronson and Kalai disagree about whether or not this unusual feat that's not very easy to relate conceptually to the ability to hit targets is a sign that the kid is plausibly going to be able to achieve traditional archery skill in the future.

Is that fair?

> If quantum supremacy was not possible, wouldn't that mean that something is wrong with our physics understanding?

Yes, but that's not outrageous. For instance, Shor's algorithm on a cryptographically interesting factorization problem would be testing the predictions of QM in a new regime (exact cancellation of a sum with roughly as many terms as the size of the product being factored, during the quantum fourier transform.) It's quite reasonable to think that QM is an approximation which will break down at that level of precision.

It is true that Gerard 't Hooft, the most famous proponent of superdeterminism is an asymptotic quantum supremacy skeptic, but I don't think superdeterminism implies no quantum supremacy. I'm a fan of superdeterminism, but I consider it to be in a pre-interpretation level of maturity, where the idea isn't even completely fleshed out. I hope that some day it can be turned into a proper interpretation like Many-Worlds and QBism, and at that point it will give all the standard predictions of QM, including the possibility of quantum supremacy.

What do you mean by “matching”? The bullish take is just a different take that presumably must develop answers to the points of this post to remain a viable belief option.

It actually strikes me somewhat as editorializing to place this link here with the wording you chose.

If anything in your linked discussion actually addresses the substantive points of this post, why not link to those items specifically? What would a generic link to discussion on it that’s not tied to this post’s claims be contributing? Why would it matter if that post was “bullish”? If it adds some context related to this post, what is that context?