Thibault Chervy on Complexity, Light and Pushing Boundaries

Dr. Thibault Chervy joined the PHI Lab in August 2021 as a Research Scientist. Previously, he was a Post-doctoral Researcher and a Visiting Scientist at ETH (Eidgenossische Technische Hochschule) Zurich in the lab of Dr. Prof. Atac Imamoglu. He received his Ph.D. in Physics at the Institute of Supramolecular Science and Engineering (ISIS), a joint research unit of the University of Strasbourg and the French National Center for Scientific Research (CNRS). 

Dr. Chervy’s main research interest is at the interface of optics and complex materials. By confining photons inside correlated and topological media, he aims to realize emergent phases of light, such as bosonic fractional quantum Hall effects and quantum spin liquids. His work also explores how complex phases of matter can be transformed by engineering their electromagnetic environment. For more on Dr. Chervy, please check out this video and read the following Q&A: 

How did you get interested in the quantum side of physics? Were you drawn early on to the ideas of emergent behavior and solid states of light?

One thing that has always fascinated me in science is how complexity can emerge from very simple sets of rules. In physics, in particular, we can summarize pretty much our whole knowledge of the fundamental rules of the universe into a couple of simple formulae. Why then do we continue to study nature? Why are we not satisfied with these concise equations? The answer is emergence and complexity. The fundamental set of rules that physicists discovered dictates the behavior of elementary particles and atoms. From that behavior whole new sets of rules are established to begin understanding chemistry, which in turn sets the stage for fundamental biochemistry, biology, and so on. What excites me the most about quantum physics is the incredible contrast between the simplicity of its set of rules, and the mind-blowing complexity of the effects that can emerge from it.

In this regard, light – composed of quantum particles called photons – is an outstanding medium to play with. We can manipulate the wavefunctions of photons with incredible accuracy, we can count individual photons arriving one-by-one on a detector, we can stir fluids of light, and so on. However, the richest emergent structures of light can only emerge if photons are able to interact with each other, which they normally don’t. That’s why we don’t have lightsabers yet. My research towards realizing emergent phases of light is mainly focused on this question: How can we make large numbers of photons interact all together?

Can you point to any professor(s) or insights you gained at ISIS that especially influenced your research?

The Institute of Supramolecular Science and Engineering in Strasbourg is a truly unique place for interdisciplinary sciences. There, under the guidance of Prof. Thomas Ebbesen, I worked in a team composed of physicists, chemists, and biologists. Our research direction was to explore how materials, chemical reactions and even biological processes could be modified by the influence of the surrounding electromagnetic environment. The incredible effect that we discovered is that even when the electromagnetic environment surrounding the molecules contains zero photons, the behavior of the molecules can be modified. In other words, the quantum fluctuations of the electromagnetic vacuum field are enough to change chemical reactivity, protein folding, and even enzymatic activity! At the time, this research direction was considered as science fiction by many researchers in the community. Prof. Ebbesen taught me to follow my intuition and to progress towards uncharted territories where theories and models do not yet exist.

While at ETH Zurich, your work involved many-body physics in cavity quantum electrodynamics (QED) environments. What kind of lab do you need to run tests in that domain? 

Studying the interplay between optics and complex systems such as fractional quantum Hall liquids of electrons requires an extreme level of control over the system. For that, you first need a roof over your head, acoustic and thermal isolation, and control over the humidity in the lab. Then you can start assembling the experiment. In our case, the sample under study had to be cooled down pretty much to absolute zero temperature to reveal its full beauty. To get there, we used a special kind of refrigerator, called a dilution fridge, cooling down our system to 100 mK – about -459.49 F. Then, we had to apply very intense magnetic fields, up to 14T – in comparison, earth’s magnetic field is only 0.00005T! When the magnet was running at full power, the researchers from the floor below us could stick their cutlery to the roof due to the fringing magnetic fields. These are extreme experimental conditions!

What conclusions did you draw from this period of research? 

The research team of Prof. Atac Imamoglu at ETH Zurich formed a very different environment from what I experienced in Strasbourg. The team was only composed of highly specialized physicists, and I had to adjust to their very rigorous language. It took me almost a year before I could understand precisely enough of their work to interact with them and become creative in this research field. After this adjustment period though, I learned everything that I needed to understand the boundary of their field, and the rest of my time at ETH was devoted to breaking out of this boundary and to venturing beyond the reach of existing theories. Along the way, we came across a few interesting discoveries, and we had a lot of fun thinking about our observations.

What attracted you to the NTT Research PHI Lab? 

The main aspect that attracted me to the PHI Lab is this interdisciplinary, curiosity-driven approach that Prof. Yoshi Yamamoto established here. It is a unique environment where researchers ranging from behavioral animal study to machine learning and quantum optics can meet and interact in view of developing new ideas and realizing them. Such an environment requires a lot of trust in the scientists and freedom for them to explore new avenues. This is exactly the kind of environment where new and unexpected ideas can flourish.

Which of your papers are your favorites or have been perhaps the most consequential?

My favorite publication out of my own work is one that came out during my time at ETH Zurich, titled “Accelerating polaritons with external electric and magnetic fields” (Phys. Rev. X 10, 011040 (2020)). This work started as a simple project aiming at observing an effect predicted by our theory colleagues from ETH and Harvard. After a few months working on the experiment with my Ph.D. student Patrick Knuppel, we realized that the expected effect would never show up. Instead of changing the subject and moving on to the next project, however, we decided to play a bit more with the sample and explore regimes that were far beyond the applicability region of the existing theories. Sure enough, we discovered a bunch of interesting new effects, and we wrote up this paper. Somewhat coincidentally, the work we are currently carrying with my team in the PHI Lab is rather directly connected to this serendipitous discovery.

Is there any current or forthcoming research with PHI Lab colleagues or external partners that you’d like to mention?

By design, research within the PHI lab is very collaborative, and we have a lot of exciting projects advancing in parallel. These days, I am particularly excited about a shared project between my team and the Lithium Niobate Team of the PHI Lab, where we are trying to interface optical modulator technologies with quantum non-linear optics experiments. We are also working very closely with colleagues in the groups of Prof. Tony Heinz in Stanford and Puneet Murthy in ETH Zurich to develop tunable arrays of non-linear quantum emitters.