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The top researcher of quantum annealing talks about its importance and the future prospects contributing to environmental issues.

In this interview, we asked the importance and the future prospects of quantum annealing to Dr. Gabriel Aeppli, who contributed greatly to the development of this quantum computing method suitable for problems where rapidly obtained but approximate solutions are what are required, with papers published when he was a researcher at the NEC North American Research Laboratory.

(This article was updated in June 2020)

Profile of Dr. Gabriel Aeppli

Dr. Gabriel Aeppli is a professor of physics at ETH Zürich and EPF Lausanne, and co-founder of the London Center of Nanotechnology and the Bio-Nano Consulting company with recent activities focused on COVID-19. He is also the founding head of the Photon Science Division of the Paul Scherrer Institute, a Swiss research facility hosting large particle accelerators for the study of matter.
He graduated from Massachusetts Institute of Technology, where he obtained a B.Sc. in Mathematics in 1978 and PhD, M.Sc. & B.Sc in Electrical Engineering in 1983. In addition to becoming a research assistant at the university, he also worked at IBM as an industrial co-op student (*1).
After working as a Distinguished Member of the Technical Staff at Bell Laboratories, he began researching quantum-related technologies in 1996 as a senior scientific researcher at NEC Labs America in Princeton.
In 2002, he became the Quain Professor (*2) of Physics at University College London, and cofounded London Centre for Nanotechnology, where he  acted as director. In April 2014, he transferred to the Swiss Federal Institutes of Technology in Zürich and Lausanne and has been a professor there since then.
An expert in quantum magnetism, he has been a member and chair of various boards and societies, and has received numerous academic awards from Japan, the United States, the United Kingdom and other countries for his achievements.
In particular, his paper "Quantum annealing of a disordered magnet", published in 1999 with three researchers when he was at NEC Labs America, contributed greatly to quantum computer research based on quantum annealing. D-Wave, the developer and marketer of the world's first quantum annealing machine, also praised the paper, which prompted the company to advance its project.
He is currently working on the application of photon science and nanotechnology for information processing and health care.

  • (*1)
    Industrial co-op student: A position for a student that is more involved in business and paid more than regular internships.
  • (*2)
    Quain Professor: A title given at University College London, to a professor who has been recognized for his/her achievements in particular fields.

Quantum computing is worth researching on because we don't know the whole picture yet

Q1Please tell us about your main research theme (specialized fields).

My original research theme was quantum and classical magnetism. Superconductivity was another research topic that attracted my interest. Superconductivity is required by some but not all types of solid-state-based quantum computer hardware.
I started my research on quantum annealing in earnest when I was at NEC Labs America which provided an ideal research environment. In particular, being able to exchange opinions with the excellent researchers around me was very important, and there were such colleagues in both the United States and Japan. We were grateful that there was an atmosphere that allowed us to focus on research themes with long time horizons for impact, but which we truly believed worth tackling.

Quantum annealing that determined the outcome of D-wave

Q1The first company commercializing quantum annealing machines, D-Wave founder Geordie Rose said at a Google workshop in 2010 that your research group's paper was a big push behind the development of their quantum annealing machine. What were the most difficult points in writing that paper?

In our paper on quantum annealing, we hypothesized that quantum tunneling would cause the system to equilibrate in a shorter time than classical barrier hopping (*3). I will explain this later, but at the time of the study, we did not know how long it would take for quantum annealing to reach equilibrium. Also, the first paper did not really prove the model of the quantum tunneling mechanism. That was fully proved in the second paper, but I remember struggling with that when we wrote the first paper. We needed to convince ourselves that the model should be correct to continue our research, even if we had not be able to prove it yet.

  • (*3)
    barrier hopping: A phenomenon in which electrons that exist in places with low energy hop and attempt to move to places with lower energy with a certain probability due to energy from the outside like heat and/or light.

Q2How do you feel when the company D-Wave came out?

I was very excited. Finally, some companies have taken our ideas seriously and tried to connect them to their business.
I met and talked with D-Wave people at conferences, and visited the company to have scientific discussions. And finally, we were able to raise funds from various companies to conduct research on the D-Wave machine.

The advantages and the academic appealing of quantum computers

Q1What are the advantages of quantum computers?

One of the advantages of quantum computers was shown in 1994 by the theoretical computer scientist and mathematician Peter Shor, saying it would be possible to produce prime factors of a large number by using a fast quantum algorithm with no known efficient implementation on a classical computer. His insight had a huge impact on the research community.
A certain type of digital cryptography widely used is based on the fact that we cannot perform large number factorization quickly enough with current digital technology, but Shor’s work implies that it can be solved with quantum computers.
It will be interesting to see how many such problems really exist, but the fact that a quarter century has elapsed and no classical algorithm as efficient as Shor’s quantum algorithm has been found increases the belief (but of course does not prove) that there are problems that classic computers cannot handle and quantum computers can solve.
Also, in principle, quantum computers can function more efficiently than classical computers. Today's computers are very inefficient and, from a thermodynamic point of view, are less efficient than, for example, modern aircraft. Flying from Tokyo to Zurich by airliner consumes considerable kerosene and produces CO2 emissions which cannot be ignored as well. But in reality, computers are even more harmful to the environment. It is said that a search on the internet can use enough energy to boil a cup of tea. From a long-term perspective, mankind will need to more seriously  exploit quantum mechanics in computers to reduce CO2 emissions.
Of course, current quantum computer designs are inefficient because they require a lot of power for cooling. However, quantum computers in the future are expected to function nearer to room temperature, and should enable highly efficient data processing in the thermodynamic sense.
I find it interesting that the topic of cooling efficiency of cloud services (*4) is discussed on NEC's website, showing that the increase in CO2 emissions due to IT technology is a major concern, and even if the same computational problem can be solved with a classic computer, in the long term, replacing it with an appropriate quantum computer should reduce energy costs and environmental load.

Q2What is the academic appeal of quantum computing for you?

I am attracted to quantum computing because even if it is theoretically possible, there are various challenges to achieve it in full form, and it is not clear how to meet them. (Laughs) It's worth researching on because we don't know  the whole picture yet.
I was interested in this field by becoming aware of Peter Shor's paper when I was at Bell Labs, and was surrounded by researchers who were actually interested in quantum mechanics at NEC Labs America, so I wished I could somehow develop an experimental demonstration of the relevance of quantum mechanics to computation. At the time, I was thinking about practical applications of quantum magnetism, one of my main research subjects, so the existence of such colleagues encouraged me very much.
Also, the famous physicist Richard Feynman had recognized the possibility of performing calculations using quantum mechanical " behavior," and I was motivated by the clear relationship between his insight and quantum computers.

(In the second part, Dr. Aeppli will talk more about quantum annealing.)