In recent years, there has been much talk about its practical application both at home and abroad.
The world is placing increasing expectations on quantum computers.
On the other hand, there are still many challenges facing current quantum computers.
It is not performing adequately.
Research on quantum computers is being conducted using a variety of approaches.
Professor Satoshi Tanamoto of the Department of Department of Information and Electronic Engineering, Faculty of Science and Engineering of Science and Technology, Teikyo University said,
By using semiconductors, we can tackle the issue from both the physical and engineering perspectives.
We are conducting research aimed at realizing quantum computers that can be widely used in society.

Both “particles” and “waves”
Quantum computing using quantum

The motion of all the objects around us and the properties of matter can be explained by mechanics (classical mechanics). For example, we can calculate the trajectory of a ball when it is kicked, the speed of an object when it falls, and even the orbit of a planet revolving around the sun. In this case, objects are considered to be "points."

However, when matter becomes extremely small, such as electrons and atoms, it behaves in a completely different way from the world of visible things. This is the world known as the "quantum." In the quantum world, objects are "particles" but also have the properties of "waves," and when in a wave state they extend into space.

Quantum computers, which take advantage of these quantum properties, can handle multiple states called "superposition states" that handle both 0 and 1 simultaneously as a "quantum entangled state," whereas conventional computers perform calculations using the binary system of 0 or 1. Utilizing this mechanism can dramatically increase the speed of calculations, so there are high hopes for it in various fields, including industry, and research and development into it is being actively conducted around the world.

"ICs (integrated circuits) that process digital signals of 1s and 0s have become increasingly miniaturized, making it possible for small machines such as smartphones to perform a wide range of functions. As a result of this pursuit of miniaturization and speed, one of the things we have arrived at is the quantum computer. However, at present there are many challenges ahead, and quantum computers have not yet demonstrated sufficient computing power," says Professor Tanamoto Satoshi.

Transistor miniaturization

The key is the "qubit"
Which type is most suitable for integration?

Quantum computers, which take advantage of these quantum properties, can handle multiple states called "superposition states" that handle both 0 and 1 simultaneously as a "quantum entangled state," whereas conventional computers perform calculations using the binary system of 0 or 1. Utilizing this mechanism can dramatically increase the speed of calculations, so there are high hopes for it in various fields, including industry, and research and development into it is being actively conducted around the world.

"ICs (integrated circuits) that process digital signals of 1s and 0s have become increasingly miniaturized, making it possible for small machines such as smartphones to perform a wide range of functions. As a result of this pursuit of miniaturization and speed, one of the things we have arrived at is the quantum computer. However, at present there are many challenges ahead, and quantum computers have not yet demonstrated sufficient computing power," says Professor Tanamoto Satoshi.

What is a quantum computer?

However, quantum computers are vulnerable to noise due to their wave nature. The currently considered most promising superconducting quantum computers can reduce noise interference by operating in an extremely low temperature environment close to absolute zero (-273°C), but they cannot be connected and used on the same board as conventional computers. In addition, there are problems with integration technology, and the number of quantum bits has not yet reached a sufficient level.

Even if it were to be put into practical use, it would not be possible to perform all calculations at high speed. Quantum computers can be broadly divided into two types: quantum gate type and annealing type, and each has its own area of expertise. Quantum gate type excels at speeding up search algorithms, while annealing type excels at combinatorial optimization problems such as traffic congestion, searching for candidate proteins for new drugs, and creating employee shifts.

"The annealing type is the one that has been put to practical use most often. For example, in material development, a huge number of combinations of materials and processing methods are tried one by one, and in the past, I think people often ended up getting by relying on experience and intuition. Quantum annealing can sometimes derive optimal solutions to problems with a huge number of combinations like this in a short amount of time. In fact, there have been reports overseas of successful cases in which quantum computers have been combined with AI to narrow down the technology needed to develop a new battery with a significantly reduced lithium content."

It has a long history and accumulated know-how
Using semiconductors brings us closer to social implementation

Professor Tanamoto's research subject is semiconductor-based quantum computers.

"A semiconductor quantum computer traps a single electron in a tiny semiconductor element and uses the electron spin as a quantum bit. With regard to the most important aspect of integrating quantum bits, semiconductors, which have many integration technologies, have a considerable advantage. In principle, multi-bits can be achieved by arranging quantum bits in a small space."

Electron Spin

A distinctive feature of Professor Tanamoto's research is that he is trying to use conventional semiconductor silicon technology as much as possible. Building a new semiconductor factory for quantum computers would cost tens of billions to over 1 trillion yen, but using existing manufacturing processes can reduce that cost considerably. Another major advantage in developing quantum computers is the abundance of experienced engineers, know-how, and development software. This perspective is particularly important to Professor Tanamoto, who has many years of experience working in the research and development department of an electronics manufacturer.

In his research, he aims to realize a quantum computer using semiconductors, and is theoretically considering the mechanism, designing the circuit, and repeatedly conducting simulations. Security technology, which is extremely important for practical application, is also one of his major research themes.

"We are currently challenging ourselves to create a three-dimensional structure. Three-dimensional structures are a trend in cutting-edge transistors, and we are hoping to incorporate them into quantum computers to increase the number of bits. If we can make it three-dimensional, we will be able to increase the computing power and add a variety of new functions. We are currently working on a precise circuit design to prevent noise that will occur when this happens."

From both science and engineering perspectives
Promoting research and development with an eye to the future

As the global competition for development intensifies, if Professor Tanamoto can demonstrate the strengths of his research, which approaches the subject from both physics and engineering, it will contribute to the social implementation of quantum computers. If that happens, the future in which quantum computers are part of everyday life may come sooner than we think.