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A researcher driving the development of quantum computers in Japan

February 22, 2022

It is said that quantum computers will have a revolutionary effect on the world. In 1999 NEC became the first company in the world to successfully demonstrate quantum bit operation using a superconducting solid-state device, thus initiating the race to develop quantum computers. Twenty years have passed since then; what kind of activities is NEC continuing now? And of what value is the quantum computer? We heard in detail from NEC’s Tsuyoshi Yamamoto, who in addition to carrying out research at the NEC-AIST Quantum Technology Cooperative Research Laboratory established in collaboration with the National Institute of Advanced Industrial Science and Technology (AIST), serves as a project manager for the development of integration technology for superconducting quantum circuits in the Cabinet Office Moonshot R&D Program.

Practical devices to solve social issues

System Platform Research Laboratories
Research Fellow
Tsuyoshi Yamamoto

―What kind of value is there in the quantum computers now being developed by companies and research institutes?

To put it briefly, they may make it possible for us to solve problems that at present cannot realistically be solved because it takes a very, very long time to do the calculations using today’s computers. Put it like that, it may sound like they are being developed out of academic interest, but it’s also of practical value. In the real world, there are plenty of problems that cannot be solved using the computers we have now.
Take for example in logistics, the problem of optimizing delivery plans. How do you allocate finite resources, like trucks and truck drivers, so as to deliver goods to their destination as efficiently as possible? It’s what in professional terms is called the ‘traveling salesman problem.’ If the goods can be delivered efficiently, you need fewer workers; less traffic congestion and a reduction in gasoline consumption should also be effective in addressing environmental problems.
Quantum computers are also expected to be put to use in the development of drugs. Today, when a pharmaceutical company develops a new drug, simulations are carried out using computers. This is because if you try to carry out experiments for each candidate substance one at a time, it takes an awful lot of effort and is very expensive. However, even if you use a supercomputer, it’s not easy to carry out simulations of actual chemical reactions involving large numbers of atoms and molecules. But if you use a quantum computer, it may be possible to do these kinds of calculations efficiently and instantly. If this were to happen, it might change the very concept of drug development; for example, we could create drugs personalized to the condition of the individual.
In addition to that, there is the possibility that we will be able to discover new ways of synthesizing the ammonia that is used in things like chemical fertilizer. At the present time ammonia is synthesized by what is called the Haber-Bosch process in a state of high temperature and high pressure, which consumes a huge amount of energy. But if we use a quantum computer, we may be able to reproduce in simulation the kind of efficient chemical reactions performed by microorganisms, and so understand that mechanism. If we can do that, we can make a huge contribution to the improvement of environmental problems.
Quantum computers can also be used in materials development. For example, superconductivity is a phenomenon in which electrical resistance becomes zero, but in order to achieve this condition under normal pressure, the substance must be cooled to at least minus 140 degrees Celsius. But a simulation using a quantum computer may enable us to understand the mechanism of superconductivity, so that we can discover substances that reach a state of superconductivity at higher temperatures. If we could find a substance that becomes superconductive even at room temperature, that would surely greatly improve our energy problems, since there would be no transmission loss of the energy put out from power plants.
In this way, quantum computers have the potential to enable us to solve all kinds of real-world problems.

Promoting projects in collaboration with various organizations in Japan

―What kind of research are you working on at present, Mr. Yamamoto?

Generally speaking, in what are called ‘quantum computers’ you have the quantum annealing method and the quantum gate method. In the New Energy and Industrial Technology Development Organization (NEDO) project, I am working on the quantum annealing method, and in the Cabinet Office Moonshot R&D Program, I am engaged mainly in research on the quantum gate method. In either case my research activities take place in the NEC-AIST Quantum Technology Cooperative Research Laboratory.
One of the biggest challenges in superconducting quantum computers is how to lengthen the coherence time. The longer the coherence time, the more complex the calculations that can be done; however, quantum coherence is like a wave that gradually decays. In particular, the annealing machines we have at present cannot yet be said to have a sufficiently long coherence time. At NEC, we are tackling this problem with a unique approach that uses a circuit called a superconducting parametron.
In comparison with the annealing method, which is specific to the combinatorial optimization problems, the quantum gate method is a more general-purpose approach. Goal 6 of the Moonshot R&D Program sets as one of its specific targets the realization by 2050 of something no one in the world has yet accomplished, what is called a ‘fault-tolerant’ quantum computer. Within that there are projects handling a number of methods, such as semiconductors or photons. I am the project manager leading the research into methods using superconducting quantum circuits. In order to achieve our target of making the quantum computer a reality, a variety of underlying technologies are needed. The technologies we need are many and varied; quantum circuit technology of course, as well as refrigerator technology to cool the chip to close to absolute zero temperature, and electronic technology for quantum circuit control. At present 17 institutions, including Japanese universities, national research institutes and private-sector companies, are working together on the project to advance research. I think this kind of activity, bringing together researchers from such diverse backgrounds and organizations to create a quantum computer, is something very unique in the world. We’re going through a process of trial and error every day, in research and engineering, in order to develop the underlying technologies needed to produce a breakthrough.

Concentrating Japan’s abilities for creative development

―On a global scale, where does NEC’s quantum computer research currently stand?

NEC is the first company in the world to have successfully demonstrated quantum bit operation using a superconducting solid-state device, but that was more than twenty years ago. In the meantime, there has been rapid progress in the development of quantum computers around the world, and it is no exaggeration to say that we are in the situation of being one or more laps behind the field. This may be partly due to the effect of insufficient resources, both human and financial. But there’s no point whining over that. The development of a quantum computer is a very long race, rather like running a hundred laps on a racetrack. If it’s a three-lap race and you're one lap behind, that might seem a hopeless situation, but it isn’t such a short race. The most dangerous thing, I think, is to misjudge the situation and give up on the race altogether. In aiming for the long-term and major goal, that is the development of a quantum computer, we want to hone our skills, and create our own originality while somehow hanging on doggedly to the leading pack.
That said, it’s not the case that the development of a quantum computer is something one company can manage on its own. Various technologies in multiple layers – the quantum circuit, of course, as well as peripheral technologies such as refrigerators and surface mounting, control electronics, computer architecture, applications, etc. – must be brought together in a single system. The development of a quantum computer has reached the stage where these kinds of things are given serious consideration. In Japan there are many organizations that each have their own strengths in such technologies. Concentration of such strengths through collaboration that goes beyond organizational boundaries, which is something we are trying in the Moonshot Project, will be the key to future progress.

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