Quantum primacy: Is it real (and if so, does it matter)?

Developers of quantum computers are vying to show that theirs can out-perform classical computers but perhaps not replace them.

The nexus of the ongoing competition among nations and corporations (such as   Google and IBM) to demonstrate quantum primacy has shifted to a university in China where not one, but two experimental quantum computers reportedly have shown that quantum primacy is attainable.

Quantum primacy is when a quantum computer is able to solve computational problems that are beyond the ability of traditional “classical” computers, yoked as they are to their quaint system of ones and zeroes.

Don’t get me wrong; classical computers long have served with distinction. So did the abacus in its day. However, as society’s computational challenges became more complex--such as splitting a restaurant bill 11 ways among your cheap and quarrelsome family members--this ancient calculating device eventually gave way to the digital calculator.

But in what Barry Sanders, director of the Institute for Quantum Science and Technology at the University of Calgary in Canada, calls a “dramatic tour de force” (his italics), research teams at the University of Science and Technology of China “may have established a hard-to-question advantage by demonstrating quantum primacy in two separate systems: one photonic, the other superconducting.”

For context, previous claims of quantum primacy apparently have drawn critiques from skeptics who wondered whether the quantum computations in question were being matched against the best algorithms or implementations that classical had to offer. Sort of like pitting a fighting robot against an overweight, middle-aged software developer with carpal tunnel syndrome. If the machine contestant prevails, can we legitimately conclude this demonstrates “robot primacy”?

This pair of experiments led by physics professor and quantum physicist Jian-Wei Pan, Sanders writes, may obviate such doubts because they went big:

The two major results by the Pan group push experimental quantum computing to far larger problem sizes, making it much harder to find classical algorithms and classical computers that can keep up. The results take us further toward trusting claims that we have indeed reached the age of computational quantum primacy.

Yet does quantum primacy really matter? Researchers at IBM argue that it may not. In throwing shade at Google’s claim in 2019 that it had achieved “quantum supremacy,” Big Blue had some rather tarty and dismissive things to say.

Google, IBM sniffed in a blog post, argues that its “device reached ‘quantum supremacy’ and that ‘a state-of-the-art supercomputer would require approximately 10,000 years to perform the equivalent task.’ We argue that an ideal simulation of the same task can be performed on a classical system in 2.5 days and with far greater fidelity. This is in fact a conservative, worst-case estimate, and we expect that with additional refinements the classical cost of the simulation can be further reduced.”

Remember, IBM also is deep into its own quantum computing research, so it’s not really clinging to the past. It merely avers that there is room in the world for the steam engine and the horse.

Quantum computers will never reign “supreme” over classical computers, IBM writes. Rather, they will work in concert “since each have their unique strengths.”

That’s not an unreasonable view, especially given that quantum computers are extremely hard to build and scale and are incredibly sensitive to environmental “noise.” Thus, you won’t see quantum computers commonly deployed commercially in the near future, never mind on the shelves of Best Buy.

Still, results of the two experiments by Chinese researchers is another sign of progress, and it’ll be interesting to see who claims the next breakthrough.

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