27 February 2018 Hugues Vincelette
Student Profile

Simon Verret obtains his doctorate in physics

Simon Verret

Photo : Fournie

Simon Verret, a member of the Institut quantique, successfully defended his doctoral thesis on February 14, 2018, and now possess a PhD in physics.

His wonder for the discipline dates back to his childhood in Quebec City. After studying Isaac Newton, he gave a lecture on gravitation to his primary school classmates. He even announces to his mother that he will do a doctorate in physics. He was far from aware of the amount of work associated with this goal. But no matter what, several years later, it was at the Université de Sherbrooke that Simon’s presentiment came true.

Although he confides that he has an interest in graphic design, he will not deviate from his scientific trajectory.

Before moving to Sherbrooke, Simon studied at the Charlesbourg campus of the Cégep de Limoilou and his bachelor’s degree in physics at Université Laval.

Simon Verret and Université de Sherbrooke on the same wavelenght

Simon was interested at first in the Université de Sherbrooke in order to study for a master’s degree in quantum information, he even approached Prs. Alexandre Blais and David Poulin.

“I did an internship at another university and I didn’t particularly like the general atmosphere. I had a good sample of the atmosphere in Sherbrooke when I met with professors from the department, including Prs. André-Marie Tremblay and Patrick Fournier during a visit. It’s not all about finding a prestigious institution or a prestigious researcher, you have to be able to have a satisfying relationship with that person and with the department.”

A reflection that takes on all its meaning, knowing that, during his bachelor’s degree, Simon worked as a student representative and that he contributed to the organization of scientific competitions.

“I came to the conviction that to study in French, there are not many places where the level of physics related to humanity in the department offers such a beautiful experience.”

He, who initially wanted to unravel the mysteries of quantum information, is now passionate about critical high-temperature superconductors, an area that is proving more complicated than he anticipated. Stimulated by the idea of discovering a less familiar scientific field, he chose to work with Prs. André-Marie Tremblay and David Sénéchal.

Graduate studies

Statistical physics, phase transitions, critical phenomena, several subjects that needed to needed more efforts at the baccalaureate level, these are exactly the areas that Simon chose to explore in graduate studies. He takes great pride in having developed expertise in these areas.

Doctoral Topic

“I had just completed my master’s degree after doing a lot of numerical computation of highly correlated systems. To predict superconductivity, to try to understand how materials become superconducting at very high temperatures, interactions are simulated using calculations and the results are observed. One of the aspects studied is a substructure in the superconducting gap of our models. I analyzed this substructure at length to realize that it was an artifact (a phenomenon created from the approximations used), not something that is physical. To illustrate, we use clusters to represent our system, rather than represent an infinite network, this cluster is repeated to reconstitute our network. A density wave is created with this repetition, as if each cluster has more electron density than the space between the clusters. Although it’s artificial, there is a link to the real materials, because in experiments we find these density waves.

So I focused on these density waves, the variations of electron density in space in 2D models that represent high-temperature superconductors. These density waves cause changes in the gap, which are substructures, they cause changes in the spectral function. I also studied electric transport in these models. Pr Louis Taillefer had experimented and achieved surprising results. So, I worked with him to interpret these experiences correctly. This is the subject of my thesis, I explained that density waves can’t cause the mysterious pseudogap of cuprates, they rather cause deformations of the superconducting gap.”

Finding Your Own Way

« Theoretical physics, like all science, must be rooted in what experience tells us,”adds Professor Tremblay.” It was with exceptional courage and rigour that Simon tackled thirty years of literature on high-temperature superconductors. He decided to use phenomenological theoretical approaches that are not usually used in our groups. This allowed him to identify its strengths and weaknesses and, above all, to help interpret the experiences of Professor Davis’s groups in Cornell and Professor Taillefer’s groups in Sherbrooke. He has become a wise man to whom theoreticians and experimenters call upon to interpret and criticize both theoretical and experimental results.”

The following steps

“My reflection is this: do I want to leave Quebec ? I’d like to come-back to that one day, I’d like to teach at the university, but I’m aware that there are more good candidates than there are positions available.”

Before choosing to answer all of these questions and now that he has completed his PhD, Simon will spend the next year working on an IQ postdoctoral project. This will allow him to continue his work while remaining close to the people he cares about. During this post-doctoral year, he intends, among other things, to tackle deep learning. Those who know Simon should not be surprised to see him exploring new fields, since for him: “It is the things that seem to us the most impermeable, that make us grow the most.”

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