Weaving an entangled web

Since China launched the world’s first quantum-enabled satellite, Micius, in 2016, the nation has sought to position itself as a leader in quantum research, a field that aims to harness the peculiar and particular properties of matter at the atomic level. The satellite, operated by a team led by Jian-Wei Pan, professor of physics at USTC, made quantum key distribution possible over long distances for the first time — technology that could lead to unhackable global communications.

Quantum-secure communication uses quantum-entangled particles, a group of particles that cannot be described independently of each other in terms of certain physical and behavioural properties, and that act as a system, even when physically far apart. In 2017, Micius enabled quantum-entangled particles to be delivered as encryption keys to researchers in ground stations near Vienna and Beijing, some 7,400 kilometres apart. The event played out as the world’s first quantum-encrypted teleconference.

Micius has helped put China, a relative latecomer to the burgeoning field, on the quantum science map. In June 2020, Pan and his team published a paper in Nature describing an experiment that further tightened the security of the communications over a distance of more than 1,120 kilometres (J. Yin et al. Nature 582, 501–505; 2020). Nations such as the United States, the United Kingdom, Japan and India are racing to develop comparable technologies.

With the potential to impart major military and economic advantages, quantum science has become a multibillion-dollar race, and China and the United States are the lead competitors. It’s a key area of focus in China’s latest five-year plan, a social and economic blueprint approved in March 2021. Pan, who is often referred to in Chinese media as ‘the father of quantum’, is encouraged to see support for the field at a national level. “We hope that … in the next five years we can make major breakthroughs in the fields of large-scale quantum communication, scalable quantum computing and simulation, and quantum metrology [the use of quantum techniques in high-precision measurement],” he says.

The United States also asserted its commitment to quantum research in March, emphasizing in an official statement on national security the need to “reinvest in retaining our scientific and technological edge and once again lead” in emerging technologies such as artificial intelligence and quantum computing.

With significant investment from tech giants including IBM, Google and Microsoft, the United States is the clear leader in quantum computing, the most high-profile segment of the field. Although China had nearly twice the number of patent filings as the United States for quantum technology overall in 2018 — including communications and cryptology devices — the United States has a significant lead in patents related to quantum computing, according to a Washington Post report based on data from market research firm Patinformatics (see go.nature.com/3b8mrte).

But China’s efforts in quantum computing are quickly gaining momentum. In December 2020, a team led by Pan and his colleague Chao-Yang Lu, also a professor of physics at USTC, claimed to be the first in the world to reliably demonstrate a quantum advantage over classical computing. A quantum advantage is achieved by performing a calculation on a quantum system, which uses quantum bits as the information carrier, that would be impossible for a classical supercomputer, which uses binary 1s and 0s, to complete. China’s quantum computer, Jiuzhang, performed a calculation in 200 seconds that would take a supercomputer 2.5 billion years to complete (H.-S. Zhong et al. Science 370, 1460—1463; 2020). It was a direct challenge to researchers at Google’s quantum-computing laboratory in Santa Barbara, California, who had made a similar claim a year earlier using their Sycamore quantum system.

The USTC and Google quantum systems have limitations. Critics say it’s unclear whether the problem Sycamore solved was truly beyond the capabilities of a conventional machine, whereas Jiuzhang is not easily reprogrammable to solve more than one problem, an issue Lu says they’re working to address. “We hope to upgrade our experiment to be fully reconfigurable by the end of this year.”

Lu says people often have “unrealistic” expectations that quantum computing will drive an imminent overhaul of all aspects of computing. They should instead consider whether or not it is a good investment, he says.“My best guess is that quantum computing will first emerge as a useful tool, like lasers, for scientists, over the next five years or so,” says Lu. “Then it might find some small-scale applications in commercial use in the following ten years.”