Difficulties facing quantum computers-technical challenges associated with increasing qubits-ZDNet Japan

About two years ago, Google achieved so-called quantum supremacy. It was a "Hello world" moment, said Sundar Pichai, the company's CEO. Achieving quantum supremacy has become a hot topic in the field, bringing quantum computing, previously a relatively obscure field of engineering, a little closer to the mainstream.

　For the first time, it was shown that quantum computers can solve computational tasks that could not be performed on classical devices in a realistic amount of time. Google's quantum processor, Sycamore, solved a problem that would take the world's largest supercomputer 10,000 years to complete in just 200 seconds.

　Since then, the quantum computing ecosystem has continued to prosper. Tech giants and smaller startups have jumped on the bandwagon. The hope is that quantum technology will one day deliver unprecedented computational power to solve problems ranging from drug discovery to financial modeling, yielding significant improvements in efficiency and business performance.

　It was a historical milestone, but the demonstration of quantum supremacy guarantees that quantum computers will eventually open up this "new era of computing". nor does it guarantee that it will be possible to develop large-scale and useful quantum systems.

There is no doubt that these are the words of the scientist who led the Google team to quantum supremacy. "Quantum supremacy was not the ultimate goal." John Martinis, who introduced quantum supremacy with Google's quantum AI team in a 2019 Nature paper, told ZDNet: "We can still go further"

Martinis has already left Google and the company's Silicon Valley campus, and has now moved to Australia where he is consulting as a system engineer at a startup called Silicon Quantum Computing. So the desire to advance the state-of-the-art of quantum computing has never gone away. "Since leaving Google, I've been thinking about a lot of things that still need to be fixed," he said.

　I'm not underestimating the importance of his experiments at Google. When Martinis joined Google's quantum AI division in 2014, the plan to achieve quantum supremacy seemed daunting. A lot of people thought it would be impossible, he recalls.

From the perspective of Mr. Martinis, who has been involved in quantum computing research since the 1980s, this project was a high-risk, high-return project and a big challenge for the team, but it still seemed feasible. Years later, he was proven right. Quantum supremacy was declared for the first time when Google's 53-qubit quantum processor performed computations that could not be done on the most powerful supercomputers.

However, there is an important caveat. Just because the Sycamore processor achieved quantum supremacy in a single computation doesn't mean Google's quantum computer can compete with conventional devices on every issue. Quite the contrary. The task the Google team designed was intended solely for quantum system solutions and had no practical use other than demonstrating quantum supremacy.

As Mr. Pichai explains in his blog post announcing the achievement of quantum supremacy, this experiment is akin to building the first rocket that can leave Earth's gravity and touch the edge of space. ing. That is, although it indicates the possibility of space travel, it is not yet possible to go to useful places.

　This is far from a declaration that it will soon be possible to travel to the moon. By the same token, achieving quantum supremacy does not mean that large-scale quantum computers will one day be able to solve scientific and business problems that cannot be addressed by conventional computers.

"I'm not sure if it will be possible to build a quantum computer," Martinis said. "The competition is nature. The real question is, will nature allow us to build a quantum computer?"