A team in China has demonstrated that it has the world’s most powerful quantum computer, leapfrogging the previous record holder, Google. Credit: Handout.

A team in China recently demonstrated that it has the world’s most powerful quantum computer, leapfrogging the previous record holder, Google.

Jian-Wei Pan at the University of Science and Technology of China (USTC) in Hefei and his colleagues say their quantum computer has solved a problem in just over an hour that would take the world’s most powerful classical supercomputer eight years to crack, and may yet be capable of exponentially higher performance.

That, and other recent announcements coming out of China have raised concerns in the US that it is losing the so-called “quantum race.”

According to a report in Scientific American, in three papers posted on arXiv.org last month, physicists at USTC reported critical advances in both quantum communication and quantum computing.

In one of the studies, researchers used nanometer-scale semiconductors called quantum dots to reliably transmit single photons — an essential resource for any quantum network — over 300 kilometers of fiber, well over 100 times farther than previous attempts.

In another, scientists improved their photonic quantum computer from 76 detected photons to 113, a dramatic upgrade to its “quantum advantage,” or how much faster it is than classical computers at one specific task.

The third paper introduced Zuchongzhi, made of 66 superconducting qubits, and performed a problem with 56 of them — a figure similar to the 53 qubits used in Google’s quantum computer Sycamore, which set a performance record in 2019.

Every additional qubit makes the quantum processor exponentially more powerful, which is why all of these advances are such a big deal.

“It’s an exciting development. I did not know that they were coming out with not one but two of these [quantum computing results] in the same week,” says Scott Aaronson, a theoretical computer scientist at the University of Texas at Austin. “That’s pretty insane.”

All three achievements are world-leading, but Zuchongzhi in particular has scientists talking because it is the first corroboration of Google’s landmark 2019 result.

“Our work establishes an unambiguous quantum computational advantage that is infeasible for classical computation in a reasonable amount of time,” the researchers explain in a preprint paper describing the experiment.

Schematic of the Zuchongzhi quantum processor, which is made of 66 superconducting qubits. (University of Science and Technology of China)

“The high-precision and programmable quantum computing platform opens a new door to explore novel many-body phenomena and implement complex quantum algorithms.”

With so many prototype quantum computers around, you might wonder why some scientists still question whether quantum computing will ever become practical technology.

That’s because the machines in use today remain experimental, and require very precise, super-cold lab conditions in order to operate, usually for very short periods of time.

None of this research is likely to be of practical use for many years to come.

But the geopolitical stakes are high: quantum networks could provide unhackable channels of communication, and a powerful quantum computer could theoretically break much of the encryption currently used to secure e-mails and Internet transactions.

Tensions between the US and China are currently at their highest point in decades, with the countries clashing over trade, human rights issues, Covid and Taiwan.

In 2019 a team at Google led by researcher John Martinis realized the so-called quantum advantage by demonstrating that the company’s Sycamore system really could perform a specific, limited task exponentially faster than even powerful classical supercomputers.

A year later USTC researchers performed a similar experiment with a quantum computer made from photons.

Why can rudimentary quantum computers beat classical supercomputers?

The common refrain goes something like this: Instead of classical bits that are 0 or 1, a quantum computer uses qubits, whose state is somewhere in between 0 and 1 prior to measurement — a so-called quantum superposition.

To work together within a computer, qubits must also be entangled, or quantum correlated with one another.

But it’s worth noting that there are different approaches to quantum computing: Zuchongzhi uses optical circuits and photons to manage and process its qubits, whereas Sycamore is based on electrons and superconductors. There can also be differences in how results are calculated and measured.

Versatility is also a vital consideration — whether a quantum computer can perform multiple tasks or just a single one that it was specifically designed for (both Sycamore and Zuchongzhi score highly here, and can take on multiple tasks).

“If you look at the West — the US, Europe — there haven’t been a lot of people talking about repeating [Google’s 2019] experiment,” Martinis says. “I admire, in China, that they want to do this seriously.”

With 56 qubits and 113 detected photons, the USTC systems are now technically the most powerful quantum computers in the world — with two big caveats.

First, neither quantum computer can do anything useful. (Photonic quantum computing is not a universal computer platform, so even scaled up, it would not be a conventional programmable computer.)

Second, it is not clear exactly how much of a quantum advantage they actually have over classical computers. Over the past few months, several studies have claimed the ability to approximate that messy entangled state, especially for photonic quantum computers.

So, is China ahead of the US in quantum information technology?

The answer depends on how you measure it.

China has more total patents across the full spectrum of quantum technology, but US companies have a dramatic lead in quantum computing patents.

And of course, China has a more sophisticated quantum network and now claims the top two quantum computers.

“It’s such a new problem for the US to be facing,” says Mitch Ambrose, a science policy analyst at the American Institute of Physics.

“It was ahead for so long, and in so many areas, that it hasn’t really had to do much thinking about what it means to be behind.”

Broadly speaking, quantum research in China is almost entirely state driven — concentrated into a few universities and companies. Research in the US, in comparison, is much more disparate — spread across dozens of universities and private companies.

Forbes Magazine reports that President Xi funded a multi-billion-dollar quantum computing mega-project with the expectation of achieving significant quantum breakthroughs by 2030.

He also committed billions to establish a Chinese National Laboratory for Quantum Information Sciences.

Examine Chinese research output over the past two years, and you’ll see that President Xi’s quantum push is working.

In December 2018, President Trump signed H.R. 6227 to fund the National Quantum Initiative Act (NQI). The law authorizes US$1.2 billion to be invested in quantum information science over five years.

A few days after the executive order was signed, the Department of Energy announced US$80 million in funding for quantum research.

Although these are positive actions, they are small compared to the enormous investments being made in quantum research by the Chinese.

We are witnessing a quantum battle that will be fought in research labs by brains instead of guns, and by scientists instead of soldiers. Moreover, the critical ammunition for this battle is research funding.

“The Chinese government is thinking about science technology very seriously, probably more than the US administration” said Zuoyue Wang, a science historian at California State Polytechnic University, Pomona.

“No one else will pick up the tab.”

Sources: Scientific American, ScienceAlert.com, ZME Science, Forbes Magazine