Hello! This is Robert from the Moonshot PR team.

Today we bring you a special interview with Professor Masahiro Kitagawa, the Program Director for Moonshot Goal 6: "Realization of a fault-tolerant universal quantum computer that will revolutionize economy, industry, and security by 2050."

Quantum computers will change the ways we approach large calculations and complex problems, overcoming the limitations of conventional digital 1s and 0s and using quantum properties instead. Yet to achieve the quantum revolution and the widespread benefits it will bring, we need ‘fault-tolerance’: the automatic detection and correction of errors during calculations. How will this be realized?

Hidetomo Honma, science communicator from the National Museum of Emerging Science and Innovation (Miraikan), talked to Professor Kitagawa to find out more.

The Potential of Quantum Computers to Solve Global Issues

Honma: Goal 6 aims to dramatically develop economy, industry, and security through the use of quantum computers. What specifically can quantum computers be used for?

Kitagawa: There are various applications. A typical example is identifying the mechanisms of chemical reactions. Living organisms exhibit highly efficient mechanisms, such as photosynthesis and nitrogen fixation by rhizobia-parasitizing legume plants. However, because these reactions involve highly complex quantum states, the mechanisms have not yet been completely identified. Since we know about most matter and the enzymes involved in the reaction, we believe that we can solve it using a quantum computer.

Honma: If artificial photosynthesis could be achieved, it could lead to solutions to various global issues.

Kitagawa: We hope to contribute to enriching people's lives by using quantum computers to solve various problems.

Honma: When did research into quantum computers begin?

Kitagawa: It was originally considered as a tool for investigating the state of matter. Unlike classical mechanics, quantum mechanics doesn't determine a single state of matter; instead it considers that various states can exist simultaneously. Even in a simple chemical reaction, there are countless states for each atom or electron, and it takes a great amount of computation to examine each one. In 1982, Richard Feynman, a U.S. physicist realized that, in order to study matters quantum mechanically, it is better to make computers themselves quantum mechanical.

Honma: That's a great shift in thinking.

Kitagawa: Subsequently, in 1994, it was found that it could solve other problems too, faster than a normal computer. This is the famous "Shor's algorithm," which can quickly perform prime factorization. After this, there was a rapid rise in interest in quantum computers.

Honma: Prime factorization is also used for internet communication cryptography, isn't it? Will it be easy to solve using a quantum computer?

Kitagawa: That's right. Since it became clear that the public-key cryptography currently in use will eventually be solved by quantum computers, new cryptography technologies that cannot be decoded even by quantum computers are now being developed around the world.

An all-Japan team leading the world with new ideas

Honma: It will still take some time before quantum computers can be put into full-scale practical use. What are the issues?

Kitagawa: The biggest challenge is to develop "error correction" technology that automatically detects and corrects errors when they occur. The technology itself has been used for some time, such as in supercomputers. Generally speaking, computers cause errors, affected by external factors, but you can use them without problems if you have the ability to correct errors, even if they occur.

Honma: If an error isn't corrected, it means that the processing progresses with the error, and the results of the process are also shifted significantly.

Kitagawa: Since the information is retained by the superposition of quantum states, the mechanism to detect the location and type of error is different from that for conventional computers. In addition, a new approach is needed to correct and recover data from errors. In 1995, Shor showed that the error correction is possible with a quantum computer, and in 2014, a superconducting quantum circuit that can continue to correct errors with a certain code was produced.

Honma: If it becomes possible to perform complex calculations, it will need to perform error correction many times, won't it?

Kitagawa: However, we cannot always correct errors yet, and it will probably take 20 to 30 years. So, in Goal 6, we decided to try to realize a fault-tolerant universal quantum computer.

Honma: What is the project structure?

Kitagawa: We are pursuing research and development by dividing the project into three areas: "hardware," "communications networks," and "theory and software." In terms of quantum hardware, we are researching four methods in parallel. Research Fellow Tsuyoshi Yamamoto of NEC Corporation, is working on the superconducting quantum methods; Assistant Professor Hiroki Takahashi of Okinawa Institute of Science and Technology Graduate University, on the ion trap method; Professor Akira Furusawa of the University of Tokyo, on the photonic quantum method; and Senior Chief Researcher Hiroyuki Mizuno of Hitachi, Ltd., on the semiconductor method.

Honma: You don't know which method is really valid, so rather than focusing on one, you need to improve the four most likely methods.

Kitagawa: Professor Hideo Kosaka of Yokohama National University is developing quantum memories and quantum interfaces to link superconducting quantum bits and telecom-band photons. Professor Takashi Yamamoto of Osaka University aims to construct a network-type quantum computer that connects multiple small- and medium-scale quantum computers. Professor Masato Koashi of the University of Tokyo is in charge of the theory and software required to achieve fault tolerance.

Honma: It is really an all-Japan collaboration, isn't it?

Kitagawa: By conducting this research and development in an integrated way, we can establish new concepts that cannot be created by studying the different elements separately, and we hope to lead the world by aiming to incorporate these findings to develop fault-tolerant quantum computers.

Getting into the world's leading group in five to ten years and high hopes for the next generation

Honma: Developments are being carried out worldwide. How do you see future trends and Japan's position?

Kitagawa: It commonly accepted in the research industry that realization of a fault-tolerant universal quantum computer is an important issue. Japan declared this as a national goal to be achieved in 30 years' time, and Japan is the first country to have come this far. It was only just in time, but it's good that this Moonshot R&D Program started. Although the research is progressing rapidly, we must get into the leading group for at least the next five to ten years. Once you leave the top, it becomes very difficult to catch up.

Honma: It is important to avoid lag because the application range is wide.

Kitagawa: By taking advantage of the computational power of quantum computers, science and engineering in general will advance, including the fields of chemistry and physics. The results will ripple through to industry and hence the economy, contributing to societal development.

Honma: Could you please give a message to our younger readers?

Kitagawa: People who are in high school now will be in leading positions in 30 years' time. I would like them to study quantum mechanics and computer science at university, and take over this field. Quantum science is a very difficult-to-understand field, but we believe it is our duty to promote it is so that younger people will develop an interest and enter the field.

Honma: It looks like it will have an impact on many people, not just on scientists.

Kitagawa: 30 years ago, only a limited number of people could use supercomputers, but now, these are right in front of you in the form of tablet computers. In the same way, quantum computers will be available to everyone in 30 years' time. Then, we may be able to solve various problems that cannot be solved now by using quantum computers. We will soon be in a world where if you clearly know what you want to do, then quantum computers will be able to do it for you.

First published on Science Japan

Moonshot Goal 6:2050

Commentary by Program Director