Sunday, August 14, 2022

Still No Quantum Supremacy

Dr. Quantum Supremacy just got back from a conference on the subject, and reports:
Of course there’s a lot still to do. Many of the talks drew an exclamation point on something I’ve been saying for the past couple years: that there’s an urgent need for better quantum supremacy experiments, which will require both theoretical and engineering advances. The experiments by Google and USTC and now Xanadu represent a big step forward for the field, but since they started being done, the classical spoofing attacks have also steadily improved, to the point that whether “quantum computational supremacy” still exists depends on exactly how you define it.

Briefly: if you measure by total operations, energy use, or CO2 footprint, then probably yes, quantum supremacy remains. But if you measure by number of seconds, then it doesn’t remain, not if you’re willing to shell out for enough cores on AWS or your favorite supercomputer. And even the quantum supremacy that does remain might eventually fall to, e.g., further improvements of the algorithm due to Gao et al. For more details, see, e.g., the now-published work of Pan, Chen, and Zhang, or this good popular summary by Adrian Cho for Science.

If the experimentalists care enough, they could easily regain the quantum lead, at least for a couple more years, by (say) repeating random circuit sampling with 72 qubits rather than 53-60, and hopefully circuit depth of 30-40 rather than just 20-25.

Considering how he has staked his professional reputation on quantum supremacy, this is an admission that it has not been achieved. It will require will require both theoretical and engineering advances, and they better come quickly, or Google and a lot of big-shots are going to be very embarrassed.

I am skeptical that quantum computers will ever have any advantage over Turing machines.

There are a lot of book hyping quantum computers. Here is a skeptical one that I have not read: Will We Ever Have a Quantum Computer?, by Mikhail I. Dyakonov.


  1. There is a very simple test for the Quantum computer to achieve that has nothing to do with how many so called 'qubits' it claims supremacy of:

    It must justify it's own expense by being useful. A quantum computer must be able to do anything that makes the money (resources) poured into its development demonstrably worth while. Inventions that save time and/or money are the hallmark of what is useful vs. what is not.

    Until this test is passed, it's just a 'bullshit dressed up in science jargon exercise' looking for government funding.

  2. Someone recently mentioned to be that there is really no difference between the supposed functioning of a Quantum Computer and an 'Improbability drive' in The Hitchhiker's Guide to the Galaxy. A model is never the reality, and never will be. A model will always be separated from reality by at least one dimension. Don't get the two mixed up or you forget what the hell you are actually operating on...and it all goes to hell from there.