Science and Innovation

Interview by Mònica Moreno for Barcelona Science and Universities and Núvol.

Leticia Tarruell specialises in quantum physics, specifically in a part of this discipline that describes the behaviour of matter of minute dimensions, such as quarks, fermions and leptons. This is a particularly dense field of the exact sciences, which is governed by rules and patterns that are different from those we know, but which, nevertheless, is the basis of many of the technologies we already enjoy. He works at the ICFO, Institute of Photonic Sciences, located in Castelldefels, an experimental centre of reference where he leads the ultra-cold quantum gas research group, a pioneering project in which, with a quantum simulator, atoms are cooled almost to absolute zero, i.e. less than -273 °C. This procedure makes it possible to manipulate matter to manipulate it in a way that allows us to make it more efficient. This procedure makes it possible to manipulate matter in order to simulate phenomena or materials that do not yet exist.

What made you decide to go into quantum physics?

Since I was very young, I have always loved physics: it is the science that explains how nature works and that, in theory, explains how everything works. I decided very early on, maybe from the age of 12, that I was going to study physics. And the particular field that I’m going into, ultra-cold atoms, like other things, was just a fluke of life. I was very interested in fundamental concepts, how things work, the universe, and this is a fundamental field, where questions are asked about quantum mechanics. And I also really liked technology, building things, making things with your hands. Quantum physics allows me to combine both: doing experiments and building big machines in the lab, with lasers, technology, which, at the same time, we use to answer fundamental questions and to know how nature works.

Quantum physics is currently of paramount importance in the development of European reference projects that could make a difference in many fields, such as engineering, chemistry or medicine. What was for a long time only a theory is being realised in practice. For the ordinary citizen, what practical applications does quantum physics have or could have in the coming years?

Quantum physics is the theory of matter on a microscopic scale. Everything is quantum. You have to understand it to know how things work. For a long time we couldn’t control a single atom or a single photon, which is the particle of light, and now we can. This has allowed ideas that were previously only abstract concepts, very interesting, to become reality and have enabled the development of applications, such as quantum measurements, which are very precise; here at the ICFO you can measure magnetic fields, put some electrodes on the brain and see what happens; you can also transfer information protected by quantum mechanics, which allows completely secure communications thanks to quantum cryptography; or calculations with quantum mechanics, which are much faster than those performed with classical computers. These are the kind of problems we study, problems of fundamental physics, like why a material behaves in a certain way. Problems that, if we were to use classical computers, such as the MareNostrum here at the BSC in Barcelona, would take longer than the age of the universe.

It remains to be worked out, but all these applications, such as better design of molecules used in different fields, from chemistry to medicine, can be done more precisely thanks to quantum mechanics.

Moreover, not all quantum technologies are at the same stage of development: quantum sensors, which allow more precise measurements, are already in use. So is quantum cryptography, which is already commercially available. But, for example, there are many people working on quantum computing, and problems can be solved, but they still need to be applied.

What is your day-to-day work like?

I work with a fantastic research group, with a lot of very good young people, who are very motivated and collaborate on different experiments. Right now we are working on three quantum simulation experiments with cold atoms, in groups of four or five people.

During the week every day in the morning we have a meeting with each of these teams and we talk about what we are doing, what problems have arisen and how to solve them. I also go to the lab to see how it is going. It has to be said that I used to spend many hours in the lab. Then we have lunch together and continue talking, and in the evening I often work on scientific papers or come up with new developments.

This work is both experimental and fundamental at the same time: very practical problems, such as the properties of a laser or how to design and screw a mechanical part, and very abstract equations are combined with theoretical collaborators.

Research is a team effort, you talk to other people. If there are a lot of people, it generates more ideas. Once every two weeks we have a general meeting and we explain what we are doing and we choose two people who explain in detail what they are doing. Other times someone presents a scientific breakthrough that they found interesting or liked, we call it a journal club, a discussion of articles.research is not something you do alone, it is done in a team and by talking to other people.

You studied physics at the Complutense University of Madrid and violin at the Conservatory at the same time. You finally opted for science, and yours seems like a full-time job. Do you still have time to play the violin?

The violin was another of my favourite things. When I was a teenager, I wanted to study physics and music at the same time, I didn’t really know what to choose. And when I started studying physics at university I decided that it was what I liked best and that I would dedicate myself to it. The truth is that I have put the violin to one side; mine is a very absorbing and also very interesting job.

In the last few months, the media often talk about ChatGPT and artificial intelligence. Do you think this technology can affect your work in any way, positively or negatively?

It is true that sometimes we use artificial intelligence in experiments: we work with complex machines, with a lot of parameters and if there is something that does not work or if we want to optimise a process, we can resort to techniques similar to artificial intelligence or genetic algorithms: you choose a group of parameters, you make one evolve randomly and you can see if it evolves well or not and make the genetic selection (this is the specific term used), I think it is necessary to see AI as a tool that will not replace people. It should be used intelligently for the more boring and repetitive tasks, which the machine can do, while people do the more interesting jobs.

Since 2013 you have been working at ICFO. This institute has a specific program that highlights the role of women in science, ICFOnians for the Women in Science Month, in which outreach activities are also held for high school students. In your career have you found female references?

I spent the last years of my studies in France and there are many women in science there. Maybe not so much in the field of physics, but I was not the only one, when I was doing my PhD I always had friends in the other laboratories. On the other hand, in Switzerland, where I did my postdoc, the situation was very different, I was the second woman in the group.

More specifically, I would like to talk about Debbie Jin, who died a few years ago. A person who was at the highest level in our field, but very accessible to lectures, dynamic and very pedagogical.

And I have colleagues in Europe, who are a bit older than me, who are also a reference. In fact, now we have created a group of women in quantum at European level, we have a chat and we have a meeting every month. It is nice to be able to talk things over with others and this initiative has arisen spontaneously.

And in your group, what is the female presence?

I am currently preparing some research projects, and this is one of the questions you get asked. We look at the number of men and women and I am delighted to say that in my direct team there are seven women and eight men.

I am very happy, when I started my career there were few women, and this has changed in the last few years. It seems to me that before the field of physics was considered something very technical and this perception is changing. It is important when there are people who serve as examples. I think this kind of interviews are important, to talk and teach girls who are finishing high school or starting university that there are also women in these fields, that there is no obstacle.

And it is also true that in a team it is very positive to have a mix of people, with different profiles, since everyone thinks differently. Men and women and also people from different countries, with somewhat different studies. This way everyone approaches scientific problems from a different perspective and better ideas are generated. Otherwise, everyone would approach things in the same way and we would be stuck.

The people who work with you, what studies have they done, are they all physicists?

Normally they are physicists, but sometimes we also collaborate with people who have studied engineering or mathematics. In the summer at ICFO we offer a program in which people from other degrees can participate. This mix is very positive, they have a more pragmatic vision or incorporate different ideas.

You have participated in several science communication and popularization projects. In addition, you are a tutor for undergraduate and master’s degree theses and doctoral dissertations. It is obvious what you offer to students, such as experience or the way of working, but what do they bring to you?

I like working in the academic world, in a research institute, precisely because many young people are involved, and I appreciate the importance of training young people. During Covid, internships were one of the things that were first cancelled, since it was considered that they could be exchanged for theory, and I found that very sad.

Young people bring a lot of ideas and are very enthusiastic, they are convinced that anything can be done. In the research teams I like to try to get them to contribute in one way or another, within their possibilities and taking into account their training. We have a summer program in which, for example, undergraduate students can participate: we divide the projects into small parts that they can carry out, and others that the master’s students carry out, which are then integrated. We try to offer them a project that is accessible to their level and that, supervised by us, they can carry out with autonomy and making certain decisions. It is a very positive experience for them and for us as well.

After a few years of studying and researching in several European countries, since 2013 you have been working at ICFO, the Institute of Photonic Sciences. How do you value science in our country? You have studied and researched abroad, you carry out many projects, what is your assessment of science here?

I started my career at the Complutense University and I finished my training and started my research in France. I was abroad for 11 years. It seems to me that science here is very theoretical, that there is the idea that you have to solve equations, that you have to make the software, but not the hardware, which is a limit, a brake.

What would you change?

There is an important division, on the one hand, scientists and on the other, engineers; in other countries it is not like that. I did my postdoc in Switzerland and there, for example, people are clear that they will dedicate themselves to theory first and then move on to business, or that they want to stay at the university, and they work in mixed teams in which sometimes people switch between a more applied or more theoretical vision, but in which they all work together.

In Spain everything is divided, and there is a lot of theory and fewer experiments are carried out. It seems to me a limitation, which is also economic, because it is more expensive to perform experiments than to solve equations. It’s a pity, because when you combine theory and experiments is when new things really come out, especially if you are looking for applications for society, we can’t stay only in theory.

We have talked about the investments needed to carry out certain experiments. You have obtained funding from many administrations. Is it difficult to present projects to receive this type of funding? Especially because politics is short term and science has to be thought of in the long term.

I dedicate an important part of my time to it: you have to plan research projects, what you want to do, for example, in three years’ time, what will be done at any given moment, what resources will be needed, how many people will be hired or why a certain thing is being done. It’s a part that I like a lot. It takes a long time to plan it well, but it is useful and interesting, it makes you think and sometimes new ideas come out.

It is also true that in the projects there is a lot of bureaucracy, a lot of administrative part, sections and more sections to fill and that, while we dedicate our time to these tasks, we don’t get our work done as scientists.

In general, I cannot complain, I have always been able to do the research I have proposed, sometimes with more effort and sometimes with less, but with a lot of hard work we have succeeded.

What advice would you give to a young woman who wants to go into science?

I think you have to follow the path you choose, do what you feel like doing. In life sometimes you have to make decisions, to choose between one thing and another. And in my life, every time I have made a decision, the right decision has always been to choose what I felt like doing, or what I found more interesting or more exciting. If you make decisions out of compromise, or from a pragmatic point of view, you usually don’t make the best choice.