## Interview with Simon Apers, CNRS Research Scientist at IRIF

Half way to 5th grade, **Simon Apers** wanted to become a medical doctor so he had to change from economics to end up in a class learning about science and mathematics. The reason why he likes this field so much is that it **uses mathematics to solve non-mathematics problems**.

Meeting with the one who just joined IRIF as **CNRS Research Scientist**.

*« I am looking into how a computer can use quantum mechanics to solve problems faster. It is very natural to use quantum computers to solve “quantum problems” in chemistry or materials science, seeing that the problems are exactly about quantum mechanical properties of a system. However, I am mostly interested in using quantum computers to solve problems that are not quantum related. »* Simon Apers, CNRS Research Scientist at IRIF | Pole Algorithms and discrete structures - Team Algorithms and complexity.

#### Tell us about your career. Have you faced any difficulties?

From 2008 to 2013, I studied at Ghent University where I did a Bachelor and a Master degree in engineering and applied physics. Physics was interesting but I didn’t like how sometimes things could not be made precise. The turning point came later on, when I first started to work on my PhD. My supervisor sent me these papers of his, and I thought that the mathematics were very intimidating. I did appreciate how he did made concepts very precise. This is when I realized that I wanted to approach things with mathematical rigour.

In 2018, I did a first postdoc jointly between Inria and CWI Amsterdam (Centrum Wiskunde & Informatica), the national research institute for mathematics and computer science in the Netherlands. During this time I worked with Anthony Leverrier on quantum error correction. I thought this was very interesting. The thing with quantum computing is that it likes to mess things up. This is why we use quantum error correction to make quantum computing a bit more robust. With Ronald de Wolf from CWI I worked on quantum algorithms for graph problems. We showed how a quantum computer can be used to compress or “sparsify” graphs in a certain sense. This is an extremely useful primitive for solving problems on graphs.

I did a second postdoc jointly between CWI Amsterdam and Université Libre de Bruxelles. In Brussels I worked more on quantum walks. These are quantum versions of random walks on graphs, and this is something that e.g. Frédéric Magniez has a lot of expertise on.

In 2021, I started working at IRIF as a CNRS Research Scientist in the pole Algorithms and discrete structures in the team Algorithms and complexity. Members of this team seek to tackle emerging algorithmic challenges and to understand the limitations of novel computational models. In quantum computation, the team tries to better understand the contribution of quantum information to computation, cryptography and communication. It is quite exciting that I can now start thinking more about long term research goals and projects, and I am very much looking forward to working with students on topics related to quantum computing.

I did face some difficulties early on since I wasn’t among the top students, my grades were not so good. Because these were the only criteria that people judged you on, I faced a lot of closed doors and rejections in my applications. This was difficult and impactful for me, but it also encouraged me to show that grades are not all that matters. Throughout, my family has always been on my side and with their endless support I made my way to where I am now.

#### What does your research work consist of?

My research interests focus on **quantum computing**. In particular, I am looking into how a computer can use quantum mechanics to solve problems faster. It is very natural to use quantum computers to solve “quantum problems” in chemistry or materials science, seeing that the problems are exactly about quantum mechanical properties of a system. However, I am mostly interested in **using quantum computers to solve problems that are not quantum related**. The most famous example is how the quantum algorithm by Peter Shor can factor numbers exponentially faster. I want to understand for which other problems we can find such speedups. For example, it would be extremely interesting to find similarly big quantum speedups for problems related to combinatorial and continuous optimization, or machine learning, and this is something that I am currently thinking about.

#### Where does your interest for theoretical computer science come from?

That’s a good question! I don’t really know… I know that I like mathematics a lot, and graphs. And I really appreciate how you can put these to work to solve actual problems. I remember that at some point I really wanted to be a physicist, because that seemed very cool. Then I thought that maybe I could be a mathematician. But now I have come to my senses, and understand that I really fit best in computer science. Within quantum computing the situation is interesting because you have both physicists and computer scientists, but it is clear that I resonate best with the latter.

#### What do you wish to develop at IRIF?

I mentioned earlier this problem I am interested in which consist of trying to use quantum computing to solve problem more efficiently. At the same time, thinking about quantum algorithms often gives a new perspective on how to solve classical problems. I am always happy when that happens. At some point, I might also be interested in **going beyond mathematics** and maybe see how to actually implement the projects I have been working on, or think more about practical heuristics for actual quantum computers. I look forward to working with the people from IRIF. There’s a large expertise, and I’m very interested in much of the research being done.

#### What would be the next steps in your career?

I look forward to building up a group, and supervise PhD and master students. In December I started teaching a course on quantum computing, which has been great. I’m mostly talking about quantum algorithms which is exactly in my field of expertise. I enjoy this educational part a lot, and it is a welcome distraction from research. In teaching, the reward is somehow fair: if you put in a lot of effort then typically it turns out well. Unfortunately, this is not necessarily the case in research, where you are often alternating between large disappointments and large surprises. Nevertheless, I am happy doing research on quantum computing. Even given all the uncertainties and how hard it is to build a quantum computer, I believe it’s a field that will pay off.

#### Do you have a professional anecdote you would like to share?

In 2014 at the conference for Young Quantum Information Scientists (YQIS) in Palaiseau (Paris), there was Alain Aspect. A famous French experimentalist and physicist with an equally famous curled moustache. He is most well-known for implementing experiments that verify quantum theory. By the end of the night, he started doing magic tricks but most of his tricks failed. Somehow, he managed to blame his PhD student for this. I figured that this is how it must go in his scientific experiments as well, and remember being very happy that I did theoretical work instead!

#### Besides science and research, what do you enjoy doing?

I like to listen to music a lot. As a Belgium citizen, I am very proud of Jacques Brel, and enjoy his music a lot. But what I enjoy most is jazz music. Django Reinhardt is to me one of the greatest jazz musicians, and it is nice to see that his music is still very much alive in Paris. Some time ago I was at jazz club called 38 Riv’, and I very much recommend this place to go and enjoy a nice concert.

#### BIOGRAPHY EXPRESS

**2021**: CNRS Research Scientist at IRIF

**2019**: Second postdoc jointly between CWI Amsterdam and Université Libre de Bruxelles

**2018**: First postdoc jointly between Inria and CWI Amsterdam

**2016**: University of Calgary, Canada for research

**2014**: Start PhD at Ghent University

**2013**: Summer internship in CERN, Geneva

**2013**: Master thesis in particle physics at Ghent University