Yao Jizhi: Quantum computing needs a lot of industry development. China still depends on imported materials and technology.

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 Yao Jizhi: Quantum computing needs a lot of industry development. China still depends on imported materials and technology.


In recent years, quantum computing and quantum computer have attracted a lot of attention in the scientific and industrial circles. Scientists hope to use the quantum properties of materials to break the Moores law of miniaturization of traditional computers and establish a new type of quantum computer. The concept of quantum computation was first introduced by Richard Feynman, a famous physicist, in 1981. Yao Shizhi, one of the early founders of this field, who won the Turing Prize, made a core contribution to the establishment of the theoretical basis of quantum computing in 1993. In 2011, Yao Jizhi founded the Quantum Information Center (CQI) of Tsinghua University, aiming to build the CQI into a world-class Center for quantum computing research. In a recent dialogue with the National Science Review (NSR), Yao Chi-chi counted the history of quantum computing and expressed his views on the future development of this field. He believes that quantum computers are good at tasks such as new material design, drug design and chemical reaction simulation, but in areas where traditional computers have proved efficient, it is unlikely to replace them.

NSR: Quantum communication and quantum computing have received extensive media attention. Are they two different concepts?

Yao Jizhi: Quantum communication and quantum computing are two interrelated but independent concepts. Quantum computing requires more advanced technology. The main goal of driving the development of quantum communication is to establish cryptographic guarantee for secure communication. In quantum communication, the signals to be transmitted from one place to another need not be highly accurate. But quantum computation requires high accuracy of signals. Over the past decade, large companies such as Google have developed some new technologies related to quantum computing. The general view is that available technologies will emerge in the next five or six years. The theoretical basis of quantum computing was established 20 years ago. Now the question is how to realize it.

NSR: Quantum computing has become a hot topic. What is its basic principle?

Yao Shizhi: With the rapid development of miniaturization of semiconductor circuits, the performance of traditional computers has been continuously improved. However, there is an inherent limit to this miniaturization: when the size of the circuit elements on the chip is reduced to nano-scale, quantum mechanical effects will dominate and affect the performance of the components. This will be the end of Moores law.

For traditional computers, this is an inevitable fate; but scientists have begun to consider whether harmful quantum phenomena in this case can be transformed into beneficial ones - building a computer that uses quantum mechanical logic described by Schrodinger equation to calculate, rather than Boolean logic. A traditional computer for computing. The concept of quantum computer was first proposed by Feynman in 1981. In principle, he says, people can design a computer that works through quantum mechanical properties, simulates quantum systems and uses quantum equations to get solutions. Feynmans idea has attracted great attention in the academic field.

Traditional computers use double-valued Boolean logic (0 and 1) to perform functions through integrated circuits. The calculation is that the input points represented by bits are mapped to a higher level, and the output points are obtained through multiple mappings to provide the final solution. However, quantum bits in quantum computers can represent 1, 0 or any superposition of these two states. The calculation of a quantum computer system is analogous to the rotation of a solid; in this analogy, the calculation of a quantum computer is analogous to the reading obtained by measuring the rotation of a solid (the rotation angle can be any continuous angle). An operation of a traditional computer corresponds to a certain path; an operation of a quantum computer can be carried out along multiple computational paths, and ultimately achieve the same goal, because the quantum wave function allows multiple states to exist at the same time. This phenomenon is quantum parallelism. Quantum parallel computing is the key reason why quantum computers can be much faster than traditional computers.

NSR: In terms of hardware design, what are the main differences between traditional computers and quantum computers?

Yao Jizhi: Quantum computer is a relatively closed system, and its calculation can be almost instantaneous. Basically, quantum computers behave very shy: once viewed, calculations are interrupted and stopped. In addition, quantum computers are very complex systems, which involve multiple frontier technologies. For example, the storage unit of quantum computer, the communication between multiple units, the modulation of quantum bit states and so on, all need to use lasers. As far as the material and manufacturing technology of quantum computer is concerned, it not only represents the integration of many advanced technologies in the past thirty or forty years, but also involves the close cooperation among various disciplines.

NSR: Does the uncertainty of quantum phenomena affect the accuracy of quantum computation?

Yao Jizhi: Yes, but an uncertain answer is not necessarily wrong. In fact, some quantum calculations always get the right answer. Moreover, as far as practical calculation is concerned, some errors are acceptable and need not be 100% accurate.

NSR: The concept of quantum computers appeared in the early 1980s, but it seems to have progressed slowly over the next few decades.

Yao Jizhi: Thats true. After Feynman put forward this idea, it was mainly physicists who were conducting in-depth theoretical exploration. It wasnt until the early 1990s, when physicists basically explained how quantum computers work, that computer scientists began to enter the field, and I myself was one of them. In 1994, PeterShor of Bell Laboratories designed a quantum computation algorithm for deciphering codes, which aroused wide interest in the computational field. The U.S. government and NASA began to invest in this field. Several competing research teams trying to build the first real quantum computer have also begun to emerge.

NSR: Since then, what have been the major developments?

Yao Jizhi: Since then, the main work has been to explore and select the scheme of realizing quantum computer. In the past decade, scientists have tried various materials, such as ion traps, superconductors and diamonds, to make quantum computers. Recently, the topological insulator has become one of the alternatives because of its excellent correctable function. But there is still a long way to go. One of the main difficulties is to keep the ultra-low temperature of the functional state.

NSR: When do you think the first quantum computer will appear?

Yao Jizhi: Many people predict that the first quantum computer will appear in the next five or six years, but I think its not easy to build a quantum computer that can perform reliable calculations at the level of thousands of quantum bits. Big companies like Google and IBM are investing heavily in quantum computer research and development. In particular, Google recruited John Marinis, the most important expert in the field, and his entire team at the University of California, Santa Barbara.

NSR: At your initiative, Tsinghua University established the Quantum Information Center (CQI) in 2011. What is the goal of this center?

Yao Jizhi: Our goal is to build a world-class Center for quantum information and to train the next generation of scientists in this field. Therefore, our top priority is to recruit high-quality researchers, such as Duan Luming, professor of Fermi Lecture at the University of Michigan. In the past few years, he has done excellent work in our center.

NSR: What are the advantages of using a diamond system?

Yao Jizhi: Diamond system has two advantages: first, it can operate at room temperature; second, it has solid crystal structure, if the system can perform well at several quantum bit levels, it may expand to a larger scale. In addition to the diamond system, our center is also working on ion traps, superconductors and photonic networks, and is making good progress.

NSR: Quantum computers have excellent performance. Will they replace traditional computers?

Yao Jizhi: I think traditional computers and quantum computers will coexist because they have their own advantages. Traditional computers have the accuracy and maturity that quantum computers do not yet possess. But compared with traditional computers, quantum computers will have advantages in solving problems involving quantum mechanical effects. For example, in the fields of material design, drug development and physical chemistry, quantum computers will show their advantages, while traditional computers are difficult to solve these problems.

NSR: The hardware and software of quantum computers are very different from those of traditional computers. What are the main challenges?

Yao Jizhi: Quantum computing is a typical interdisciplinary field, which requires close cooperation between scientists and engineers in related fields, especially between quantum physicists and computer scientists. Breakthroughs in algorithms will stimulate improvements in hardware, and vice versa. For example, Professor PeterShor, who I mentioned above, not only proved that quantum computing can solve the problem of cryptographic cracking, but also the problem of error correction in quantum computing. Based on his research, physicists began to believe in the feasibility of quantum computers. When quantum computer develops to a certain stage, it will need the change of computer science. Traditional computer data storage, computing systems and programming languages need to be redesigned. It is not clear how this will be accomplished, but this is an important research direction. Many leading IT companies have already built a number of projects to develop quantum software.

The research of quantum computing methods and algorithms is a field with great potential. Over the past few decades, there have been several elegant computational methods that are theoretically attractive. I would like to see more quantum computational methods that are practical, such as those for material design.

NSR: Does quantum computing seem to require the co-development of science and manufacturing technology?

Yao Jizhi: Thats right. I have emphasized that in China, the importance of making quantum computers is far greater than just studying quantum computing, because it will drive the development of related technology industries. Such large-scale projects will stimulate the potential of scientists and engineers, who will create new methods and technologies to solve specific problems. These methods and technologies can make beneficial contributions to society in many fields such as industrial development, national security and so on. In the actual experiment, there will be some immediate concerns. For example, diamond materials suitable for quantum computers depend on foreign imports. When competition becomes more intense, other countries may refuse to sell us materials. If we do not develop these materials on our own, the future will be easily limited. In addition, working in this field, it is impossible to publish articles needed for personal evaluation and promotion in a short time. Unless we change the existing evaluation system, it will be difficult to motivate researchers to engage in such basic research. All this leads us to still rely on imported materials and technologies. (Pu Muming: Director of Institute of Neuroscience, Chinese Academy of Sciences, Executive Editor of NSR; Wang Ling: Special Writer of NSR) Source of this article: Science and Technology Daily - Responsible Editor of China Science and Technology Network: Wang Fengzhi_NT2541

Yao Jizhi: Thats right. I have emphasized that in China, the importance of making quantum computers is far greater than just studying quantum computing, because it will drive the development of related technology industries. Such large-scale projects will stimulate the potential of scientists and engineers, who will create new methods and technologies to solve specific problems. These methods and technologies can make beneficial contributions to society in many fields such as industrial development, national security and so on.

In the actual experiment, there will be some immediate concerns. For example, diamond materials suitable for quantum computers depend on foreign imports. When competition becomes more intense, other countries may refuse to sell us materials. If we do not develop these materials on our own, the future will be easily limited. In addition, working in this field, it is impossible to publish articles needed for personal evaluation and promotion in a short time. Unless we change the existing evaluation system, it will be difficult to motivate researchers to engage in such basic research. All this leads us to still rely on imported materials and technologies.

(Pu Muming: Director of Institute of Neuroscience, Chinese Academy of Sciences, Executive Editor of NSR; Wang Ling: Special Writer of NSR)