Pan Jianwei: Quantum technology is related to national strategy and can only be achieved through continuous breakthroughs and innovations

▲ On May 26, 2015, Pan Jianwei was debugging equipment in the laboratory of USTC Shanghai Institute. Photo by Zhang Duan/This magazine

◆ The achievements of "Jiuzhang" and "Zu Chongzhi II" have made my country the only country to achieve "quantum computing superiority" in both physical systems, firmly establishing its position in the international frontier of quantum computing research.

Original title: Pan Jianwei, academician of the Chinese Academy of Sciences: Quantum technology is related to national strategy and can only be achieved through continuous breakthroughs and innovations

Text丨Xu Haitao, Zhou Chang, and Chen Nuo, reporters of Outlook News Weekly

In August 2016, the "Mozi" quantum science experimental satellite was launched into space, marking my country's leading position in global quantum communication research. In December 2020, the University of Science and Technology of China announced that Pan Jianwei and others at the school had successfully built a 76-photon quantum computing prototype "Jiuzhang", making my country the second country in the world to achieve "quantum computing superiority". In October 2021, the 113-photon 144-mode quantum computing prototype "Jiuzhang II" was announced.

From "Mozi" to "Jiuzhang-2", what remains unchanged in the mind of Pan Jianwei, an academician of the Chinese Academy of Sciences, is the exploration of the quantum world and the pursuit of the development of quantum technology in my country.

Pan Jianwei told Outlook News Weekly that quantum technology is related to national strategy. With the "big things of the country" in mind, we must continue to make breakthroughs and innovations, and strive to explore a more flexible, efficient, and resource-integrated collaborative innovation path to ensure that my country's quantum technology development always stays at the forefront of the world.

“Chinese people can also do good scientific research”

"Outlook": Why is the world's first quantum science experimental satellite named "Mozi"?

Pan Jianwei: I feel very relaxed watching the launch video now, but in fact, 30 seconds before the launch, I kept clasping my hands together, hoping that the satellite could successfully enter space. The satellite was named "Mozi" because Mozi was a "scientific saint" in Chinese history. I want to tell everyone that Chinese people can also do good scientific research.

Mozi lived 2,400 years ago. He advocated universal love and non-aggression, that is, equality and fraternity, and opposed war. In the Mohist Classic, he proposed that "stopping is due to a long time, and there is no long time without stopping", which means that the reason why an object stops is mainly because of the action of force. If there is no resistance, the movement of an object will never stop. This is actually the same concept as Newton's first law of motion. In addition, Mozi conducted a pinhole imaging experiment more than 2,000 years ago. We know that this phenomenon only occurs when light propagates in a straight line.

We named the world's first quantum science experimental satellite "Mozi", on the one hand to commemorate Mozi's achievements in optical research, and on the other hand to demonstrate our cultural confidence.

"Outlook": What role does "Mozi" play?

Pan Jianwei: Using quantum satellites to establish a quantum communication network can cover all kinds of islands, ocean-going ships, overseas institutions and other places that are difficult or impossible to reach with optical fiber, thus ensuring the security of my country's information transmission around the world. The experiment of "Mozi" has fully verified this feasibility.

"Micius" has successfully completed three major scientific experimental tasks. On this basis, it has also completed the docking of "Micius" and "Beijing-Shanghai Trunk Line", realizing intercontinental quantum secure communication. In addition, "Micius" also provides a new platform for testing basic physics problems such as the integration of quantum mechanics and gravity.

Quantum computing research is at the forefront internationally

"Outlook": What is the significance of successfully building the quantum computing prototype "Jiuzhang"?

Pan Jianwei: According to the best classical algorithm at the time, the speed of computing Gaussian boson sampling problem by Jiuzhang is one hundred trillion times faster than the world's fastest supercomputer, Fugaku, making it the second computer in the world to achieve "quantum computing superiority". The name Jiuzhang was chosen to commemorate the famous ancient Chinese mathematical monograph Jiuzhang Suanshu.

It actually took us 20 years of hard work to achieve this breakthrough in 2020. The breakthrough of Jiuzhang mainly overcame three major technical difficulties: high-quality quantum light source, high-precision phase-locked technology, and large-scale interference technology.

Since the beginning of this year, our team has carried out a series of conceptual and technological innovations, and recently successfully developed the "Jiuzhang II". We have three major breakthroughs. First, we have significantly improved the yield, quality and collection efficiency of quantum light sources, and increased the key indicators of light sources from 63% to 92%. Secondly, we increased the multi-photon quantum interference circuit from 100 dimensions to 144 dimensions, and increased the number of manipulated photons from 76 to 113. Third, we added programmable functions.

The results show that the computing power of Jiuzhang-2 has been greatly improved. According to the best classical algorithm published so far, the processing speed of Jiuzhang-2 in solving the Gaussian boson sampling problem is a billion billion times faster than the world's fastest supercomputer and 10 billion times faster than the 76-photon Jiuzhang. At present, Jiuzhang-2 is only a "single champion" and can only solve the specific problem of Gaussian boson sampling, but the solution to this problem has potential application value in graph theory, quantum chemistry and other fields.

"Outlook": Quantum computing includes multiple technical routes. What is my country's layout in superconducting quantum computing?

Pan Jianwei: In addition to optical quantum computing, we also have a good layout in the direction of superconducting quantum computing.

In May this year, we built the 62-bit superconducting quantum computing prototype "Zu Chongzhi", which had the largest number of superconducting quantum bits at that time, and realized programmable two-dimensional quantum walks. Based on the "Zu Chongzhi", we adopted a new flip-chip 3D packaging process to solve the problem of large-scale bit integration, and successfully developed the "Zu Chongzhi No. 2", which achieved high-density integration of 66 data bits, 110 coupling bits, and 11-way reading. Through quantum programming, we have achieved the sampling of quantum random circuits and demonstrated the programming ability of "Zu Chongzhi No. 2" to execute arbitrary quantum algorithms. According to the currently disclosed optimized classical algorithm, the processing speed of "Zu Chongzhi No. 2" for quantum random circuit sampling problems is more than 10 million times faster than the fastest supercomputer currently, and about 40,000 times faster than Google's similar prototype "Planeta".

The achievements of "Jiuzhang" and "Zu Chongzhi II" have made my country the only country that has achieved "quantum computing superiority" in both physical systems, firmly establishing its position in the international forefront of quantum computing research.

Advancing Quantum Information Strategic Technology

"Outlook": What will the development of quantum information technology bring us?

Pan Jianwei: Quantum information technology is not only a strategic technology for my country, but has also become an important strategic layout for major developed countries in Europe and the United States. Just as transistors are the basis of computers, laser technology is an important support for the modern Internet, and the development of navigation technology is inseparable from the support of precision measurement technologies such as atomic clocks... The establishment of quantum mechanics has directly led to the development of modern information technology. After more than a hundred years of development, quantum mechanics has made technical preparations for solving some of the problems we are currently facing.

Quantum communication provides a communication method that is unconditionally secure in principle and can significantly improve the security of existing information systems.

The computing power of quantum computing increases exponentially with the increase in the number of quantum bits. The ability of quantum computing to perform parallel operations can be used to decompose large numbers and solve linear equations. For example, it takes 150,000 years to decompose a 300-bit large number using a trillion-times classical computer, but it only takes 1 second using a trillion-times quantum computer. Therefore, quantum computing has shown great potential and can be used in a variety of applications such as classical code breaking, weather forecasting, financial analysis, drug design, and revealing the mechanisms of new energy and new materials.

Outlook: What is your next goal?

Pan Jianwei: In the field of quantum computing, the international academic community has defined three phased goals, and the first phase goal has been achieved. The second phase is to complete the principle of quantum error correction and develop a dedicated quantum simulator that coherently manipulates hundreds of quantum bits, which will be applied to specific problems such as combinatorial optimization, quantum chemistry, and machine learning, and guide material design and drug development. It will take 5 to 10 years to reach this stage, which is the current main research task.

In the field of quantum communication, we hope to develop complete space-ground integrated wide-area quantum communication technologies through 10 to 15 years of efforts, and promote the widespread application of quantum communication in finance, government affairs, energy and other fields. At the same time, we will use the high-precision optical quantum transmission technology and space quantum science experimental platform developed by wide-area quantum communication to build a high-precision time and frequency transmission network, making an important contribution to the next generation of "second" definition. On this basis, we hope to carry out research on basic physics problems such as gravitational wave detection and dark matter search.

Published in Outlook, Issue 51, 2021

Source: Outlook

Executive Producer | Shi Xiangzhou

Producer | Yang Yue

Editor | Tang Duoduo