Hartmut Neven, the founder and lead at Google Quantum AI, says Google's new Willow quantum chip is so fast it may be borrowing computational power from other universes in the multiverse.

It does not lend credence to the notion at all, that statement doesn't even make sense. Quantum computing is inline with the predictions of quantum mechanics, it is not new physics, it is engineering, the implementation of physics we already know to build stuff, so it does not even make sense to suggest engineering something is "discovering" something fundamentally new about nature.

MWI is just a philosophical worldview from people who dislike that quantum theory is random. Outcomes of experiments are nondeterministic. Bell's theorem proves you cannot simply interpret the nondeterminism as chaos, because any attempt to introduce a deterministic outcome at all would violate other known laws of physics, so you have to just accept it is nondeterministic.

MWI proponents, who really dislike nondeterminism (for some reason I don't particularly understand) came up with a "clever" workaround. Rather than interpreting probability distributions as just that, probability distributions, you instead interpret them as physical objects in an infinite-dimensional space. Let's say I flip four coins so the possible outcomes are HH, HT, TH, and TT, and each you can assign a probability value to. Rather than interpreting the probability values as the likelihood of events occurring, you interpret the "faceness" property of the coin as a multi-dimensional property that is physically "stretched" in four dimensions, where the amount it is "stretched" depends upon those values. For example, if the probabilities are 25% HH, 0% HT, 25% TH, and 50% TT, you interpret it as if the coin's "faceness" property is physically stretched out in four physical dimensions of 0.25 HH, 0 HT, 0.25 TH, and 0.5 TT.

Of course, in real quantum mechanics, it gets even more complicated than this because probability amplitudes are complex-valued, so you have an additional degree of freedom, so this would be an eight-dimensional physical space the "quantum" coins (like electron spin state) would be stretched out in. Additionally, notice how the number of dimensions depends upon the number of possible outcomes, which would grow exponentially by 2^N the more coins you have under consideration. MWI proponents thus posit that each description like this is actually just a limited description due to a limited perspective. In reality, the dimensions of this physical space would be 2^N where N=number of possible states of all particles in the entire universe, so basically infinite. The whole universe is a single giant infinite-dimensional object propagating through this infinite-dimensional space, something they called the "universal wave function."

If you believe this, then it kind of restores determinism. If there is a 50% probability a photon will reflect off of a beam splitter and a 50% probability it will pass through, what MWI argues is that there is in fact a 100% chance it will pass through and be reflected simulateously, because it basically is stretched out in proportions of 0.5 going both directions. When the observer goes to observe it, the observer themselves also would get stretched out in those proportions, of both simulateously seeing it it pass through and be reflected. Since this outcome is guaranteed, it is deterministic.

But why do we only perceive a single outcome? MWI proponents chalk it up to how our consciousness interprets the world, that it forms models based on a limited perspective, and these perspectives become separated from each other in the universal wave function during a process known as decoherence. This leads to an illusion that only a single perspective can be seen at a time, that even though the human observer is actually stretched out across all possible outcomes, they only believe they can perceive one of them at a time, and which one we settle on is random, I guess kind of like the blue-black/white-gold dress thing, your brain just kind of picks one at random, but the randomness is apparent rather than real.

This whole story really is not necessary if you are just fine with saying the outcome is random. There is nothing about quantum computers that changes this story. Crazy David has a bad habit of publishing embarrassingly bad papers in favor of MWI. One paper he defends MWI with a false dichotomy pitching MWI as if its only competition is Copenhagen, then straw manning Copenhagen by equating it to an objective collapse model, which no supporter of this interpretation I am aware of would ever agree to this characterization of it.

Another paper where he brings up quantum computing, he basically just argues that MWI must be right because it gives a more intuitive understanding of how quantum computing actually provides an advantage, that it delegates subtasks to different branches of the multiverse. It's bizarre to me how anyone could think something being "intuitive" or not (it's debatable whether or not it even is more intuitive) is evidence in favor of it. At best, it is an argument in favor of utility: if you personally find MWI intuitive (I don't) and it helps you solve problems, then have at ya, but pretending this somehow is evidence that there really is a multiverse makes no sense.