A photo of the Jiuzhang light-based quantum computer prototype Photo: courtesy of University of Science and Technology of China 

A research team led by renowned Chinese quantum physicists Pan Jianwei and Lu Chaoyang announced Friday that they have established a new light-based quantum computer prototype and demonstrated "quantum advantage," a term to describe the point where quantum computers can do things beyond the capability of non-quantum, or classical computers.

This is the second time a quantum algorithm has claimed to achieve this feat in the world, after a first claimed by Google's Sycamore device in 2019. Lu Chaoyang, a professor of the University of Science and Technology of China in Hefei, capital of East China's Anhui Province, who plays a key leading role in the research team, told the Global Times on Friday that their quantum computer has multiple advantages over its Google counterpart.

Named Jiuzhang after an ancient Chinese mathematical text, the new quantum computer developed by the Chinese research team beats Sycamore in three aspects - computational speed, environmental suitability and computing power on problems with larger samples, Lu noted.

The Jiuzhang research team published their achievement in Science magazine online. In the study, the Hefei team, led by Pan and Lu, chose Gaussian boson sampling (GBS), a classical simulation algorithm, to provide a highly efficient way of demonstrating quantum computational speed in solving some well-defined tasks.

The Jiuzhang could find solutions to the boson-sampling problem in 200 seconds, which will take Sunway Taihulight, the current fourth most powerful supercomputer, 2.5 billion years to do the same.

According to a statement Pan's assistant sent to the Global Times on Friday, Jiuzhang is 100 trillion times faster than the most powerful supercomputer of today, and 10 billion times faster than Google's Sycamore.

Such an achievement shows that China has conquered the first milestone in the field of quantum computing study, Jiuzhang developers said.

"Although Jiuzhang and Sycamore are designed to handle different tasks, computational speed can be regarded as the most important indicator of advancement," Lu told the Global Times, citing a Chinese saying, "in the world of kung fu, speed defines the winner." 

A photo of the Jiuzhang light-based quantum computer prototype Photo: courtesy of University of Science and Technology of China

Compared to Google's Sycamore device which has 53 quantum bits (qubits) made from superconducting circuits that are kept at ultralow temperatures, Jiuzhang is also more environmentally adaptable as almost all of its parts, except the detection section, can operate at room temperature, Lu said. 

Sycamore must operate at temperatures around -273 degrees Celsius, he said.

Jiuzhang also has bigger computing power on larger samples than Sycamore on certain calculations, Lu said. 

"For an analogy, Sycamore can beat supercomputers only at short-distance runs, but Jiuzhang excels at both long- and short-distance races," he added.

Science and technology blogger Yuan Lanfeng compares this bigger computing power of Jiuzhang to the stronger calculating ability of a longer abacus as opposed to a shorter one. 

"In theory, Jiuzhang can deal with more complex calculations than Sycamore," Yuan, who is also an associate researcher at National Research Center for Microscale Material Science under USTC, told the Global Times.

The establishment of Jiuzhang marks China's advancement on the path to full-scale quantum computational advantage, which was commonly referred to as "quantum supremacy" in the Western world.

Though it sounds "provocative," quantum supremacy is an academic rather than political concept, Yuan said. 

"Here, the 'supremacy' indicates that quantum computers have far stronger computing ability than classical supercomputers, or quantum computers can solve problems that supercomputers are incapable of solving," he told the Global Times on Friday.

This is the first time that quantum advantage has been demonstrated using light or photonics," Christian Weedbrook, chief executive of quantum-computing startup Xanadu in Toronto, Canada, was quoted by the New Scientist magazine website on Thursday.

"This is certainly a tour de force experiment, and an important milestone," says physicist Ian Walmsley at Imperial College London. And he said the Chinese team's claim of quantum advantage is convincing. 

Matter of time

However, many Chinese observers and foreign experts pointed out that as yet, and in contrast to Google's Sycamore, the Chinese team's photonic circuit is not programmable, so "it cannot be used for solving practical problems."

Lu added that if the team is able to build an efficient enough programmable chip, several important computational problems could be solved. Among those are predicting how proteins dock to one another and how molecules vibrate, Lu said.

Compared with conventional computers, Jiuzhang is just a "champion in one area," but its super-computing capacity has application potentials in areas such as graph theory, machine learning and quantum chemistry, according to the team.

Weedbrook also notes that photonic quantum computing started later than the other approaches, but could now "potentially leap-frog the rest." At any rate, he adds, "It is only a matter of time before quantum computers will leave classical computers in the dust."

"Compared to some US tech giants, including IBM, that have started exploring the possible uses of quantum computers in practical fields such as the development of new materials, quantum computing in China is still at the stage of thesis and laboratory," Guo Guoping, founder and chief scientist of Chinese quantum company Origin Quantum Computing, told the Global Times

Quantum computing is expected to bring transformative innovations to people. This technology, though still unfamiliar to most people, would be closely linked to people's health and daily lives in the future, Yuan said.

Despite the distance between reality and imagination, experts are very optimistic about the future, and believe that quantum computers will bring about revolutionary innovation to the world, as their applications will be not limited to esoteric puzzles, but to improvements in daily life.

Yuan mentioned the traffic congestions that people usually encounter, saying he guesses the annoying traffic jams will be largely improved with the help of quantum computing, which can rapidly calculate huge amounts of traffic information and soon adjust the length of every related traffic light to the optimal value based on the calculation results.

Quantum computing can also be used to develop antiviral drugs with its great retrieval and computing power that can quickly find out the most suitable molecular structure of the drug, Yuan said.

"Some infectious viruses, such as the COVID-19, may be soon eliminated in an era of quantum computing, as drugs may soon be developed," he said.