Google's quantum computing supremacy claim relies on a synthetic benchmark, researchers assert

Quantum computing researchers in academia and firms in competition with Google are dismissing claims of quantum supremacy, though note that this is still a significant milestone toward it.

Why post-quantum encryption will be critical to protect current classical computers Quantum computers are theorized to be capable of breaking RSA encryption. Experts disagree on when it could happen, but agree on a need for quantum-proof encryption.

Nature published on Wednesday the finalized version of the Google paper claiming quantum supremacy that leaked in September, leading to widespread criticism among the quantum computing industry. Google's claim, at its core, is that their 53-qubit "Sycamore" computer is capable of performing a test calculation in 200 seconds "that would have taken the best known algorithms in the most powerful supercomputers thousands of years to accomplish," CEO Sundar Pichai said in a blog post

The industry objection to this claim is that the calculation in question is of no practical use outside of research laboratories—even inside labs, the utility of it does not extend meaningfully beyond the synthetic benchmark scenario Google pursued for this paper. 

SEE: Quantum computing: An insider's guide (free PDF) (TechRepublic)

Pichai likens the benchmark to the Wright brothers, in an interview with MIT Technology Review. "The first plane flew only for 12 seconds, and so there is no practical application of that. But it showed the possibility that a plane could fly." 

He also dismisses criticism of their use of "quantum supremacy" as implying quantum computers will eventually outperform classical computers on all fronts, though quantum computers are likely to need to work with classical computers as an accelerator, like GPUs and in-memory computing solutions.

"It is a technical term of art. People in the community understand exactly what the milestone means," Pichai said. 

John Preskill, professor of theoretical physics at the California Institute of Technology, coined the term "quantum supremacy" in 2012. Preskill downplayed the meaningfulness of Google's claim, noting that "the problem their machine solved with astounding speed was carefully chosen just for the purpose of demonstrating the quantum computer's superiority," in a column in Quanta Magazine. "This quantum computation has very little structure, which makes it harder for the classical computer to keep up, but also means that the answer is not very informative."

Despite this, Preskill recognizes the demonstration as significant. "Now that we know the hardware is working, we can begin the search for more useful applications," he added.

IBM, which rolled out its own 53-qubit system in September, takes a significantly cooler stance toward Google's claims. In a post written by Edwin Pednault, John Gunnels, and Jay Gambetta, IBM argues "an ideal simulation of the same task can be performed on a classical system in 2.5 days and with far greater fidelity," claiming this is a "a conservative, worst-case estimate," and arguing that Google's synthetic benchmark does not meet the threshold of quantum supremacy as defined by Preskill.

Further, IBM notes the hazard of printing headlines that exclaim variations of "Quantum Supremacy Achieved" as "inevitably [misleading] the general public," though notes that "Google's experiment is an excellent demonstration of the progress in superconducting-based quantum computing, showing state-of-the-art gate fidelities on a 53-qubit device, but it should not be viewed as proof that quantum computers are 'supreme' over classical computers."

Scott Aaronson, author of Quantum Computing Since Democritus and professor of computer science at the University of Texas atAustin, takes a middle ground approach to the issue, criticizing the overhyping and dismissal of Google's claim. 

"Have a little respect for the immensity of what we're talking about here, and for the terrifying engineering that's needed to make it reality," Aaronson wrote.

"Before quantum supremacy, by definition, the [quantum computing] skeptics can all laugh to each other that, for all the billions of dollars spent over 20+ years, still no quantum computer has even once been used to solve any problem faster than your laptop could solve it, or at least not in any way that depended on its being a quantum computer. In a post-quantum-supremacy world, that's no longer the case."

"The dismissiveness I'm seeing in some corners of the Internet is kind of breathtaking to me. It's like, if you believed that useful air travel was fundamentally impossible, then seeing a dinky wooden propeller plane keep itself aloft wouldn't refute your belief … but it sure as hell shouldn't reassure you either."

For more on quantum computing, check out "Why quantum volume is vital for plotting the path to quantum advantage" and "Aliro aims to make quantum computers usable by traditional programmers" at TechRepublic.

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