Prof. Hélène Perrin studies the quantum world at near-absolute zero and tells us more about the situation of women in quantum physics in France
Hélène Perrin is a quantum physicist working on quantum gas at Laboratoire de physique des lasers of the Université Sorbonne Paris Nord and at CNRS, the French National Centre for Scientific Research where she is a research director and leads the Bose-Einstein Condensate group (short: BEC group). In her research, she focuses on experimental atomic physics with ultracold atoms, including Bose-Einstein condensation, low dimensional quantum gases and their superfluid dynamics. Perrin also leads the network QuanTiP – Quantum Technologies in Paris Region that brings together world-class academic teams as well as companies in Paris Region in the field of quantum technologies.
Dear Professor Perrin, thank you very much for taking the time to speak with atom*innen. Could you give us some insights into your current research?
Over the past few years, my research group has focused on ultracold atoms in reduced dimensions. In practice, this involves confining the atoms so that they can only move in one or two directions.
Reducing dimensionality enhances fluctuations compared to the usual three-dimensional case, making the systems particularly interesting for us. All of this takes place at extremely low temperatures, where the motion of the atoms is very limited. Under these conditions, the atoms no longer behave individually, but collectively, forming what are known as quantum gases. In our Bose–Einstein condensate group, we focus on bosons. Bosons are known to gather in the same quantum state when the temperature falls below a certain threshold. My main focus has been on two-dimensional systems, and we have recently studied the dynamics of quantum gases in these systems.
One of our most recent experiments involved setting these gases into rotation. As they are quantum gases, they behave as superfluids, meaning they do not rotate like ordinary liquids such as water. If they are rotated gently, they do not move at all. If they are rotated very quickly, rather than forming a single large vortex at the centre, many tiny vortices develop. Each of these vortices is quantised and linked to a discrete value of velocity circulation. We investigate these vortices, looking at how they arrange themselves and how they move. In another experiment, we have just produced a gas confined to one dimension. Here, our focus is on manipulating pairs of atoms using microwave radiation. By applying microwaves, we can bind two atoms in the gas together to form a molecule. Interestingly, the formation of these molecules also leads to controlled losses of the trapped atoms. This enables us to remove atoms from the system quickly, a process that can be exploited for further studies.
A quick follow-up, if I may: How cold is ultracold?
Temperature is measured in degrees. In physics, we use a different reference point to that used in everyday life when we talk about temperature. Rather than starting from 0 °C, we measure from absolute zero — the lowest possible temperature, which is -273.15 °C. This is defined as 0 kelvin (0 K). In our experiments, we work extremely close to absolute zero, just a few billionths of a degree above it. To give you an idea of the scale, think of it this way: one degree is one kelvin and one thousandth of a degree is one millikelvin. Here, we are talking about one billionth of a degree, or one nanokelvin. Our quantum gases typically reach temperatures of about 10 or 20 nanokelvins. In terms of motion, at room temperature, atoms move at hundreds of meters per second, not kilometers per hour. At nanokelvin temperatures, they move at less than one millimeter per second.
That's absolutely fascinating. Have you always been this passionate about physics? What made you decide to become a physicist?
As a child, I wasn't particularly drawn to physics, I was definitely more of a “maths girl”. I think this is because I didn’t encounter inspiring physics teacher for a long time. By contrast, I had excellent maths teachers, so pursuing that path felt natural. After completing my baccalaureate, I enrolled in the French classes préparatoires, which are intensive programmes combining mathematics, physics and other subjects. During the first year, I was still leaning strongly towards mathematics. But then, I had an outstanding physics teacher for the first time. This completely changed my perspective. While mathematics was becoming increasingly theoretical and abstract for me, physics suddenly revealed itself to be really interesting. When it came to applying to Grandes écoles, I was accepted by several institutions and decided to choose the École polytechnique. When I first heard about quantum mechanics, I immediately fell in love with it. It offered a lot of math but also many strange things that are not intuitive and that I would not have expected. And that was so much fun.
This experience convinced me to change direction, take every physics option available. So ultimately, I would say it was the influence of an excellent teacher and my discovery of quantum mechanics that set me firmly on the path to becoming a physicist.
What you have just shared with us highlights the importance of encouragement and positive role models. Taking a broader view, could you tell us a little more about the situation of women in physics in France?
Until the mid-1980s, there were separate Écoles normales supérieures for girls and boys in France. These schools were designed to train future teachers and university lecturers and professors, with a certain number of places available to women in subjects such as mathematics and physics. In the 1980s, there was a heated debate about merging these schools. In the natural sciences, the impact was a disaster: After the merge, the number of female mathematics students dropped to almost zero; in the first year of the unified school, only one woman was admitted among forty mathematics students. Physics experienced a similar decline. This shift had long-term consequences. Women born before the mid-1960s had the advantage of strong female role models in academia, many of whom came from the separate ENS institutions. My own generation, however, did not have that advantage, resulting in a lower proportion of women entering the field. Since then, the percentage of women in physics has remained relatively low overall.
How does this situation manifest itself in the current academic landscape? For example, how many women are currently pursuing a PhD in physics in France?
Currently, around 30% of physics PhD students in France are women. However, this proportion decreases at every stage of their careers. In my own field at the CNRS, for example, women represent only around 18–19% of permanent researchers. One measure implemented to counterbalance this is the requirement for scientific committees to include at least 40% women. While this is well-intentioned, in practice it often means the same senior women are repeatedly asked to serve on committees. This creates a significant administrative burden, which is not usually formally recognized when careers are evaluated. This results in less time for research, which can inadvertently hinder the very careers we aim to support. Despite France once having a relatively strong pipeline of women in academia thanks to the old ENS system, this legacy has faded. Today, we are confronted with many of the same structural barriers and imbalances that are found elsewhere in the world.
If you could select a few tools or measures to improve the situation for women in physics or science more broadly, which ones would you choose?
One important aspect is how we evaluate scientific careers. Gaining visibility in the scientific community often depends on receiving invitations to conferences rather than serving on countless committees. As someone with three children, there were periods when I found it difficult to remain visible or attend major events. This is why I believe we should make a conscious effort to invite more women, particularly younger ones, to conferences. It’s worth asking ourselves: Have we overlooked anyone? Are there any excellent female scientists who are less visible simply because they are less mobile?
Another issue is, like I said, the imbalance in committee work. This additional administrative work takes time away from research and can hinder career progression. Perhaps we should reconsider how we value these collective contributions. In my experience, women often invest a lot in community-oriented work. If such engagement were recognised and valued equally alongside research output, academia could become more inclusive overall. It might even encourage men to engage more in these shared responsibilities. As a young scientist, I would also have insisted more on protecting my research time, particularly for attending conferences and presenting my work. Conferences are not just about visibility; they are often the places where opportunities, collaborations and new ideas are formed.
Practical support is also, of course, essential. Providing childcare at conferences or offering grants to help with costs would make it much easier for scientists with young children to maintain an active and visible presence in their field. This could prevent many talented women from feeling forced to choose between family and career.
Academic mobility can present specific challenges for women. Would you say that's something you've also noticed?
Mobility can be a major challenge. If you want to pursue an academic career, you are expected to move, often internationally, which can be very difficult if you have a family. Institutions should do more to support families who relocate, for example by offering childcare support or helping partners find employment. When I defended my PhD, I was eight months pregnant. I couldn’t imagine moving abroad with a newborn, so I took a postdoctoral position near Paris instead. I was fortunate to secure a permanent CNRS position at the age of 27, which would be much more difficult today. Early stability is crucial, and we need to consider how the system can accommodate different life paths.
What advice would you give to young women interested in a career in quantum science?
Above all, don’t underestimate yourself. I’ve supervised many talented young women who doubted their ability to complete a PhD, but those doubts were unfounded. Also, build your network. Talk to other women in science, seek mentors, and don't hesitate to ask researchers you admire for advice. Having mentors who will genuinely support and empower you can make all the difference. Having the right people around you will help you stay confident and resilient throughout your academic journey.
Learn more about Hélène Perrin here.
Author: Karoline Irschara
published on 2025-11-11