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.

Wednesday, August 10, 2022

New Lecture on Many-Worlds

Physicist Sean M. Carroll has a new lecture on The Many Worlds of Quantum Mechanics. Here is a 2-year-old lecture on the same subject.

A question at 1:04:00 asks for observable evidence for many-worlds. For example, could you prepare a Schroedinger Cat, and somehow verify that it is alive in one world and dead in another?

The correct answer is that there is no such evidence, and the whole concept of many-worlds is unscientific and unverifiable.

He dodges the question, and says that there are experiments that could disprove quantum mechanics.

Yes, of course, but textbook (aka Copenhagen) QM does not say the two cats can be observed.

His lecture is a pretty clear explanation of QM and many-worlds.

He says, at 35:40 that many-worlds is a theory, not an interpretation. I agree with that. The interpretations of QM all have the same predictions and observations. The interpretation is just a philosophical explanation for what the variables mean, but no experiment can say that one interpretation is any better than any other.

The Copenhagen interpretation is what Bohr and Heisenberg said. And maybe Schroedinger and Dirac. The textbook interpretation is the version of it found in modern textbooks.

Many-worlds is, in essence, the theory of QM with the part about observations and predictions removed. So many-worlds cannot make predictions, and cannot be tested or verified.

Carroll is a big proponent of many-worlds, but only because he believes it gives a better explanation of what is going on. But it does not explain anything, and is an unscientific theory.

In the older lecture, he admits at 37:00 that many-worlds cannot be tested. He excuses this by saying that the assumptions that go into many-worlds can be tested. Those assumptions are the same as with quantum mechanics, so every test of QM is also a test of many-worlds.

This is just a dodge. There is no test that can show a preference to many-worlds over textbook QM.

He then goes on to say that many-worlds is an unfinished theory, maybe some day someone will figure how many-worlds could make testable predictions. With the current knowledge of the theory, it deterministically predicts that all things happen in branched universes, so all predictions come true in some universe. The theory cannot be tested.

Israeli physicist Lev Vaidman has a new paper on Why the Many-Worlds Interpretation?:

A brief (subjective) description of the state of the art of the many-worlds interpretation of quantum mechanics (MWI) is presented. It is argued that the MWI is the only interpretation which removes action at a distance and randomness from quantum theory. Limitations of the MWI regarding questions of probability which can be legitimately asked are specified.... Some speculations about misconceptions, which apparently prevent the MWI to be in the consensus, are mentioned.
I give you arguments for many-worlds, as otherwise you would not believe that the theory is as stupid as it is.

Note that he says that MWI removes randomness and fails to predict probability, as if that were an advantage.

The only part of our experience, which unitary evolution of the universal wave function does not explain, is the statistics of the results of quantum experiments we performed. ...

Thus, the MWI brings back determinism to scientific description [8]. (Before the quantum revolution, determinism was considered as a virtue of scientific explanation.) We, as agents capable of experiencing only a single world, have an illusion of randomness. This illusion is explained by a deterministic theory of the universe which includes all worlds together.

Got that? It it deterministic about things we never see and fails to predict the probabilistic events we do see.
The MWI provides simple answers to almost all quantum paradoxes. Schr ̈odinger’s Cat is absurd in one world, but unproblematic when it represents one world with a live cat and a multitude of worlds with the cat which died at different times of detection of the radioactive decay. ...

The paradoxical behaviour of Bell-type experiments disappears when quantum measure- ment does not have a single outcome [9]. ...

The reluctance of a human to accept the MWI is natural. We would like to think that we are the center of the Universe: that the Sun, together with other stars, moves around Earth, that our Galaxy is the center of the Universe, and we are unhappy to accept that there are many parallel copies of us which are apparently not less important.

There you go. Your rejection of the idea that you are constanting splitting into parallel universes is just a natural human conceit about your own self-importance. You are like those narrow-minded astronomers who put the Earth at the center of the universe.

This is crackpot stuff. It is anti-science. It is saying that you can get paradoxes out of a theory by removing all predictions.

Monday, August 8, 2022

Grad Schools to Stop Using Standardized Tests

From an AAAS Science magazine editorial:
Earlier this year, the University of Michigan became the first US university to remove the requirement that applicants to its nonprofessional doctoral programs take a standardized test—the Graduate Record Examination (GRE). This decision will not, on its own, address inequities in admissions practice, nor the broader education barriers that many applicants face. But it is a major step toward an admissions process that considers all dimensions of a candidate’s preparation and promise—a holistic view that should be adopted by all universities if equity in education and opportunities is to be achieved. ...

What are the costs for admissions committees that use the GRE in admissions decisions? In short, the loss of talented applicants at every stage of the process.

This is the dumbing down of science grad schools. The purpose is to admit incompetent women and BIPOCs. There is no example of a talented applicant being lost. The talented ones are able to score well on the tests.

Test scores are the main way that talented students get into good schools, when they have deficiencies in their records. Ignoring the scores serves no purpose, example to enable sex and race discrimination. It is amazing to see America's leading science journal going along with this nonsense.

Google Quantum Computers Failed to Prove Anything

AAAS Science magazine announces:
Ordinary computers can beat Google’s quantum computer after all
Superfast algorithm put crimp in 2019 claim that Google’s machine had achieved “quantum supremacy”

If the quantum computing era dawned 3 years ago, its rising sun may have ducked behind a cloud. In 2019, Google researchers claimed they had passed a milestone known as quantum supremacy when their quantum computer Sycamore performed in 200 seconds an abstruse calculation they said would tie up a supercomputer for 10,000 years. Now, scientists in China have done the computation in a few hours with ordinary processors. A supercomputer, they say, could beat Sycamore outright.

Such results were reported previous on this blog, and by Gil Kilai, who points out that Google was wrong by ten orders of magnitude.
“I think they’re right that if they had access to a big enough supercomputer, they could have simulated the … task in a matter of seconds,” says Scott Aaronson, a computer scientist at the University of Texas, Austin. The advance takes a bit of the shine off Google’s claim, says Greg Kuperberg, a mathematician at the University of California, Davis. “Getting to 300 feet from the summit is less exciting than getting to the summit.”

Still, the promise of quantum computing remains undimmed, Kuperberg and others say.

No, they are not 300 feet from the summit. They are still at sea level.

The whole point of quantum supremacy is to find a computation where quantum computers are demonstrably faster that classical (Turing) computers. That has been a failure. No advantage has been shown at all.

The advance underscores the pitfalls of racing a quantum computer against a conventional one, researchers say. “There’s an urgent need for better quantum supremacy experiments,” Aaronson says. Zhang suggests a more practical approach: “We should find some real-world applications to demonstrate the quantum advantage.”
They are acknowledging that no quantum computer has demonstrated any advantage.

I have said here that the whole research program is misguided and doomed. Quantum computing is probably impossible.

Even if you didn't know anything about this subject, you would have to think the program is fishy. The QC proponents are collecting billions of dollars in research funds, and making wildly exaggerated claims, only to be proved wrong later. Look at how they are in denial. The biggest result of the last ten years is proven wrong, and they still say, "the promise of quantum computing remains undimmed".

Thursday, August 4, 2022

The Prize for the Electroweak Model

The biggest Nobel Prize for the Standard Model was probably the 1979 prize to Glashow, Weinberg, and Salam for electroweak theory.

Peter Woit posted some info about bickering behind the prize. Apparently Salam's work was unoriginal and undeserving. Salam thought that he deserved to share the 1957 prize for parity violation, and lobbied heavily to get it for something else.

Apparenly also Weinberg used to be close buddies with Glashow, but did not want to share the prize with him. So Weinberg was eager to credit Salam in order to cut Glashow out.

I am not even sure Weinberg was so deserving. His contribution was a short 1967 paper that was not hardly cited by anyone, Decades later prizes were given for the Higgs mechanism and 'tHooft renormalization, and they were arguably more critical.

A couple of comments mention that Salam was the first Moslem to win a science prize. I do not know if that worked in his favor, or against him.