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Igor Ferrier-Barbut: Exploring light on the atomic scale

Researcher portraits Article published on 30 March 2023 , Updated on 13 April 2023

Igor Ferrier-Barbut is a researcher at the Charles Fabry Laboratory  (LCF - Univ. Paris-Saclay, Institut d'Optique Graduate School IOGS, National Centre for Scientific Research CNRS). He tests light scattering through a variety of experiments on different systems at the atomic scale. His extremely encouraging work has recently earned him a research grant from the European Research Council (ERC) and the 2022 Jacques Herbrand Prize from the Academy of Science.

The son and grandson of researchers, Igor Ferrier-Barbut has lived in the midst of science since he was just a child. After obtaining his Bachelor's degree in Physics in 2009 at the Joseph Fourier University in Grenoble (now Université Grenoble Alpes), he did the first year in a Master's degree in Berkeley and then came back to Paris for a Master's degree in Quantum Physics at the Ecole normale supérieure (ENS Ulm campus). He then defended his PhD thesis in late 2014 at the Kastler Brossel Laboratory (LKB - CNRS, Collège de France, ENS -PSL, Sorbonne Univ.). The young physicist then went to Stuttgart, Germany, to perfect his knowledge of cold atoms for a little over three years, as part of his post-doctorate study. In 2018, he was hired as a CNRS research fellow at the Charles Fabry Laboratory (LCF). 


Fundamental physics with large numbers of particles 

Specialising in optics, in various fields, including atomic physics for a major part, the LCF employs about one hundred people, including around forty permanent researchers. Igor Ferrier-Barbut is a member of the "Atoms" team in the "Quantum Optics" group, whose leader is Antoine Browaeys. The laboratory's quantum optics activities date back to the work of Alain Aspect, who won the Nobel Prize in Physics in 2022.

"Doing fundamental physics with large numbers of particles with systems in atomic physics is my core activity. I try to solve problems that are simple to ask but very difficult to solve," summarises the physicist. He explores the scattering of light by performing experiments to better understand its interaction with matter. "Describing the overall collective behaviour of a system containing a large number of atoms becomes very difficult when they are interacting with each other, especially when it comes to systems described by the laws of quantum physics." So the researcher builds N-body systems (with a large number of particles) with his team, using several different methods. 


Toing and froing between theory and experience

For Igor Ferrier-Barbut, quantum optics is both a tool for preparing experiments and an object for measuring the interaction of light with the atomic ensemble. "We know that a set of atoms that collectively emits light can be an interesting resource because it is, for example, very stable. It can thus be used for very precise metrology measurements. Now, we are able to describe an atom which interacts with the light quite well, but as soon as we start to study a lot of them at the same time, the problem becomes too complex to solve," explains the researcher. "We therefore make approximations and sometimes even predictions. These are tested in experiments because we know that they can be placed in a regime where the approximations are not verified. It is this toing and froing between theory and experiment that allows us to move forward," adds the physicist.


A better control of light 

After starting this research with the DEAR project (Dissipation-Engineered Atom Arrays), funded by the French National Research Agency (ANR), Igor Ferrier-Barbut continued with the CORSAIR project (Controlled Subradiance in Atomic Arrays), and won an ERC Starting Grant from the European Research Council, which started in September 2022. This research grant gives him the necessary means to build a new experimental platform over a period of five years that will allow unprecedented access and optimal control of each individual atom, based on the manipulation of single atoms of dysprosium. The challenge today is to succeed in manipulating each one of them in order to identify precisely how they emit light. "Thanks to CORSAIR, we will observe and measure what creates correlations and vice versa, and how these correlations are at the origin of a light field that differs from the classical one we would expect," the researcher explains.

A first experiment in an extremely simple system allowed him to observe extremely interesting collective effects in free space, in particular a state in which the atoms emit light in unison and continuously. "This came as a surprise," says the researcher. "This phase transition (out of equilibrium) had been predicted but nobody expected that it could be done in an experiment in such a simple way. The system under study behaves collectively in a way that is different from the sum of all the constituents taken separately."
The next step in the project is to study individual photons directly. "This will allow us to characterise the arrival times of the photons and their organisation, which will give us plenty of information about the nature of the light emitted."


"Most researchers like to talk about their work." 

Igor Ferrier-Barbut's winning of the Jacques Herbrand Prize from the French Academy of Sciences in October 2022, which every year rewards young mathematicians or physicists (under 35 years old), has brought his work right into the spotlight. "I appreciate the encouragement this award represents for the team and the laboratory. I was lucky enough to have met the right people," says the young physicist, who benefits from the worldwide reputation of his LCF colleagues, Antoine Browaeys and Thierry Lahaye.

He enjoys sharing his research, whether by teaching first-year students at the Optic Institute Graduate School and those in the 2nd-year of Master's degree Quantum, Light, Materials and Nano Sciences at Université Paris-Saclay, or by taking an active part in the organisation of the Science Fair in his laboratory, which this year attracted numerous students from all levels of study at the University, thanks to the Nobel Prize in Physics awarded to Alain Aspect. "One of the advantages of this exceptional environment is the ability to recruit excellent students," concludes Igor Ferrier-Barbut. They are the ones doing the research. My role is to motivate them by highlighting the positive outcomes of their experiments, while also mapping out the perspective of their ideas."


Igor Ferrier-Barbut