Prof. Michèle Leduc talks about pioneering Bose-Einstein condensation of helium and building lasers from scratch, and why scientific integrity matters more than ever
Michèle Leduc is Research Director emeritus at CNRS in Laboratoire Kastler-Brossel at École normale supérieure in Paris. Her scientific career began in the 1960s with groundbreaking work on optical pumping of helium and the development of new infrared lasers, particularly the LNA (lanthanum neodymium magnesium hexaluminate) solid-state lasers. These technologies found applications not only in quantum physics but also in medical imaging, specifically for magnetic resonance imaging of lungs using hyperpolarized gases.
In the 1990s, she joined the cold atoms group led by Nobel laureate Claude Cohen-Tannoudji, where she played a key role in observing Bose-Einstein condensation of metastable helium in 2001 – a milestone in modern physics.
Alongside her research, Leduc held numerous leadership positions: she directed the Laboratoire Kastler-Brossel, served for ten years as director of IFRAF (Institute for Cold Atoms in the Paris region), and was president of the French Physical Society. Furthermore, Prof. Leduc dedicates many efforts into ethics and scientific integrity: for example, from 2012 to 2021, she chaired the CNRS Ethics Committee (COMETS) and was instrumental in shaping France's National Charter of Ethics for Public Research Professions. She was a member of the Scientific Council of the French Office for Scientific Integrity (CoFIS) and is now a member of the Committee for Scientific Integrity at Académie des Sciences.
PHOTO CREDIT: Jean-François Dars
Professor Leduc, it is a great honor to be speaking with you today. To begin with, let us go back to the early days of your impressive career: Could you tell us a little about your background and what sparked your interest in physics?
My journey into physics was not exactly straightforward. At school, I excelled in many subjects and found many things genuinely interesting: Literature was my real passion. I was also drawn to science, although initially I was more interested in chemistry than physics, largely because of the experiments involving liquids changing color, and so on.
It was actually my parents who steered me towards physics and mathematics. They wanted me to have what they called a 'proper job'. My mother was very feminist, and in her own way she managed to keep me on track. Nevertheless, after my first year of preparatory studies, I seriously considered switching to literature, primarily because of my mathematics teacher. What saved me, if you can call it that, was winning first prize in a competition. Suddenly, all the professors were telling my parents that I absolutely must not change course. I was eighteen and listened to them, which is how I ended up at the École normale.
Once there, I chose physics over mathematics because I was being realistic (or perhaps even modest) as I thought that to become a mathematician, you really had to be a genius. I was a good student, nothing more. I thought physics would suit me better, especially since I have always enjoyed practical work. Gradually, I became increasingly drawn to experimental physics.
Was there a particular moment when you knew you wanted to specialize in quantum physics?
That wasn't my original plan at all. I first tried nuclear physics, but it turned out not to be right for me. Working in a huge team was not very rewarding, and it was difficult to see the impact of your work. Also: If something went wrong, I wasn't the person to fix it; I had to depend on technicians and so on. Furthermore, I found the community and environment unappealing. I also became ill, likely due to radiation exposure in the lab where safety standards were inadequate and people did not care much. So, I decided to quit.
I visited many laboratories while looking for a new direction and a PhD position. Believe it or not, many labs refused me simply because I was a woman. One professor of solid-state physics even said, "If this girl enters my lab, I will quit."
At some point, I went to the laboratories of Prof. Kastler and Prof. Brossel. They were different and had no objections to women working in their labs – quite the opposite, in fact. They offered me a one-year trial, after which they kept me on. I have always admired them and am enormously grateful. As it happened, I joined the lab right before Kastler was awarded the Nobel Prize, which turned the lab upside down. Perfect timing!
It sounds like you were very fascinated to enter this world. I suppose that doing research in physics involves many joys and challenges. Could you tell us about a piece of research you found particularly exciting?
Being a scientist is not an easy job, probably everyone knows that. Most of the time you might not succeed. You get home wondering what you’ll do tomorrow, next week or next year. Is this the right way to do things? It can also cause anxiety. However, when something really works, the joy is so immense that it gives you the energy to keep going. There were many exciting moments in my career. One moment I remember vividly is when I finally achieved something that people thought was impossible. In the early days of lasers, I wanted to develop a laser that could be used for optical pumping at the helium wavelength. Such lasers did not exist; you could not simply buy one – you had to build it yourself. One advantage of that time was that there was less pressure, so I had the opportunity to explore many different possibilities. When I finally found a solution that worked, I was overjoyed. This opened up so many possibilities for the future.
Another example I can give you is as follows: I conducted numerous experiments involving these particular lasers and nuclear polarisation of helium-3 gas. Together with my German colleagues, I came up with the idea of getting humans to inhale this gas and then imaging their lungs using nuclear magnetic resonance imaging (NMR). Nobody in my lab believed it would be possible; all the predictions were that it would not work. However, we managed to conduct a test of this lung imaging, and when the first image of the lungs appeared immediately on the first attempt, it came as a shock – a positive one. It was a great success. We opened champagne. Today, this is an established diagnostic tool used in medical research, for example in asthma research.
You mentioned less pressure to publish in earlier decades. What has changed?
I see a lot of differences when I compare the beginning of my career in the 1970s/1980s with the situation for PhD students or postdocs today. Initially, we were under much less pressure to publish numerous papers. For example, a gap of one or two years without a significant publication was not a major issue. I worked on developing a particular laser for helium and tried many different approaches, but I did not publish anything significant during this period. However, this did not damage my career at all. I had a position and my supervisor told me to take my time. When I talk to doctoral students and postdocs in the lab today, I realize how difficult it is for them. The list of publications required for certain positions is immense, and the number of permanent research positions is declining.
All this pressure may also present new ethical challenges. You are very committed to ethics in science. For example, you chaired the CNRS Ethics Committee for almost a decade, and you currently serve as an ethics expert for the European Commission. Could you tell us how you became involved in this area?
It was all by chance. When I was asked if I was interested in heading the CNRS ethics committee, I had absolutely no particular competence in ethics. The president of the committee nominated me, but initially I did not understand why. The only reason I could think of was my connection to Kastler, who was always interested in ethical issues. For example, he was against the use of nuclear weapons in warfare and was concerned about how people share and discuss knowledge. He also worked to support Jewish physicists from the Soviet Union (the 'refuseniks'), who were forbidden to emigrate from their country. I suspect I was co-opted because some of those values were associated with me.
Then I had to learn ethics from scratch. I found it very interesting: I read a lot, attended lectures and had the unusual privilege of being able to select the twelve members of the committee myself, so I surrounded myself with trusted individuals and we developed the committee together. This committee lasted ten years.
What are the most pressing ethical issues in science today?
I would argue that there are many issues. It's not just about scientific integrity; it's also about asking questions such as: Can and should science still claim to be neutral? Is science necessarily neutral? When I was on the CNRS committee at the start, our position was clear: keep your identity as a researcher within a certain institution separate from your political activities as a citizen. In other words, science should not be used for political gain. This has changed now. If we take climate change as an example, we know that we are heading towards a wall, so this 'old' position will no longer suffice. The new question is whether scientists have a special responsibility to speak out. This is a new challenge: how to balance responsibility with neutrality.
Another current challenge concerns the pressure that scientists face nowadays, as mentioned previously. Sometimes, scientists may conduct their research too quickly. We all attend conferences, listen to lectures and so on. There is also the problem of plagiarism, which is not always obvious (for example, plagiarism of ideas). This also happens in physics, even though it is often a self-correcting field. If you publish something, it is usually double-checked by your colleagues. In my lab, which is a top lab where three Nobel prizes have been awarded, you might think that things like faking results don't happen. But I can tell you: They did happen here too. For example, a few people falsified their results slightly. If nobody can reproduce your marvelous results, something is usually wrong. Now, we have specific training for PhDs and I was involved in making it compulsory because I think it is fundamental for everyone.
A rather new challenge is how AI affects scientific integrity. We all use AI, e.g. to write articles. It becomes very difficult to know what you have done yourself and what the AI tool has done. It can also be a major source of errors, so you must actually check everything thoroughly. If you don't do this, it can lead to a lot of mistakes. I advise being completely clear about what you have used the tool for; all of this must be clearly stated. Was it at the conception stage, when writing the article or finding sources? I see this as a new risk.
Moving on to the topic of women in physics: Could you share your experiences as a woman in the field? Did you find it difficult to find your place? What challenges did you face?
As mentioned before, many labs didn't want me at all. I was happy to be accepted into the labs of Kastler and Brossel, who were also keen to have more women in their labs as there were very few at the time. I was an exception. I would put it like this: I wasn't treated badly, but I wasn't encouraged either. I remember finding the first two years very difficult, as a competitor published something I wanted to publish before me. I also felt alone; my supervisor left to pursue other opportunities in the US. I had problems, and it was tempting to give up on research – after all, I had all the qualifications I needed to become a high school teacher. All my male colleagues told me I should become a high school teacher (which would also be good if I ever had children later on). However, there was one colleague who told me that I should stay in research, find a new subject and keep working. To this day, I admire him greatly.
Later in my career, I didn't experience any problems with poor treatment. My career progression was pretty normal and good. However, I would like to share the following story with you: I was working in a team with a male colleague who was at the same level as me. Whenever a visitor came to the lab, he always took the lead in explaining things. I was simply excluded from the conversation. I was invisible. When we eventually achieved a significant result together, he received the award. Not me. Even though we had both been equally involved. I found that deeply discouraging, and ultimately, I left the group and changed fields. I was awarded many times after that, but that particular moment in the middle of my career was significant for me.
One more thing: I was never asked to join the Academy of Technology, even if I already had everything needed to do so – many big projects and grants. I would always have liked to be asked to be part of it, but I was a woman at the wrong time.
I'm sure this has improved nowadays, but there's still a clear problem when you look at the numbers. Today, there are still very few women in quantum physics in France, and the number is declining rather than increasing. At high school level, physics and other hard sciences are still presented as being too difficult for girls or as being very abstract and far away from everyday life. Stereotypes are still very prevalent; we assign different roles to girls and boys and these expectations are very hard to dispel.
Throughout your career, you have demonstrated a strong commitment to addressing issues affecting women in physics and science. For example, you have been an active member of 'Femmes & Sciences' since its foundation, and you are addressing the issue of harassment in higher education. How important has collaboration, networking and solidarity among women scientists been in your experience?
I have always enjoyed being part of such groups. For example, Femmes & Sciences started out as a very small group of women in mathematics and physics. More and more people joined the group, which was then extended to include other disciplines, such as the social sciences. Compared to many other associations that struggle to gain new members, this particular group is growing tremendously. They run training sessions for girls in high schools, do outreach work and hold conferences, among many other activities. I think it's important for girls to have professional women, preferably young, they can relate to. They go to schools and tell girls what they do and why they like doing it. The questions the girls ask can sometimes be very surprising. They often ask personal questions, such as: 'Do you have a husband? Do you have children? How do you manage?' The idea that research and family life are incompatible seems to be a widespread belief, even in France.
What advice would you give to young women today who are interested in pursuing a career in quantum science?
I would tell them not to be afraid of having children and wanting a family as well as a career in research. Don't worry too much. Your children will be happy if you are happy, and they can probably manage more than you think they can. For example, my children had to do their homework themselves, but they managed just fine.
Another piece of advice I would offer is: Choose your partner carefully. This can make a big difference. Remember that you are not just your partner's wife and that his/their job comes first. Your job is equal to your partner's. You are not second; you are equal. This is important from both a professional and a personal perspective. There needs to be a balance. Trust yourself and don’t lose faith just because of what you hear from your friends or colleagues (e.g. 'You do too much; you should relax').
A critical period for women is when they have children. It's a time when you have less time for research, you're tired and you publish less than your colleagues. When you are in competition with others, don't tell yourself, 'I'm not as good as them because my list is too short'; tell yourself, 'Yes, I published less and I'm not as productive, but I'm still as good as them.' Don’t compare yourself too much to others and recognize your own potential.
Is there anything else you would like the atom*innen community to know about?
Regarding quantum physics in general, be careful not to be misled by hype. There needs to be a balance between hype and hope. At the moment, Quantum Physics is very popular, with lots of grants and funding available. However, you should not promise more than you can deliver. Many people think they will achieve the quantum computer, but there is also a tendency to promise too much eluding the intrinsic limits of the technology. However, you can be confident that fundamental physics underlies everything. All of our current research will contribute to tomorrow's knowledge, and we will never have enough of that.
Dear Prof. Michèle Leduc, it was a great pleasure to talk with you. Thank you very much for sharing your knowledge, your experiences and stories with us!
If you want to learn more about Michèle Leduc, you can check:
- Michele LEDUC - Laboratoire Kastler Brossel
- Honorary Fellows: Dr Michèle Leduc | Institute of Physic
- "Elles sont l'avenir des sciences" : Entretien avec Michèle Leduc - Union rationaliste
- Michèle Leduc on Wikipedia
Author: Karoline Irschara
published on 2026-09-11