Sophie Rochette earns her PhD

Defend a thesis online

Photo : IQ - Maxime Dion

It is difficult to ignore the COVID-19 global pandemic in the spring of 2020, even when it comes to the doctoral thesis defence of a student from the Department of Physics and member of the Institut quantique (IQ). On May 15, Sophie Rochette defended her doctoral thesis virtually. For the first time, the doctoral student and the jury were all in a different location, but this did not prevent the researcher from completing her studies as she conducted them, brilliantly.

“At the beginning of the year, when I started the last stretch of my research work, I imagined myself doing my public defence as is usually the case for each person who defends their thesis, that is to say in an amphitheatre, surrounded by familiar faces. In this sense, it’s a little frustrating, but once the frustration had passed, I found that it is a nice challenge, an opportunity to do things differently, even it there are some technical obstacles to overcome,” shares the recipient of a PhD degree.

In the end, more than 100 people attended the defense live via different online platforms. “Even if I would have liked to have been able to experience this step with my loved ones and my colleagues, I am very happy to see that the online event allowed people who could not have been part of this during normal times to join me.”

Sophie Rochette is not afraid of firsts: she initiated the first meetings of the Regroupement des femmes en physique de l’Université de Sherbrooke in 2016, which later became the Comité Diversité en Physique de l’Université de Sherbrooke. In 2018, she contributed with her colleagues Marie-Eve Boulanger and Maude Liziaire to the organization of the 7th Women in Physics Canada Conference (WIPC). It was the first time that this event was held on Quebec soil. This successful project has won several accolades to its organizers, such as the Mérite estrien and a prize at the Gala Force Avenir.

Sciences at CEGEP

Influenced by reading Québec Science and various science fiction books at the start of high school, Sophie Rochette dreams of astrophysics. This interest in science leads her to the Cégep Régional Lanaudière in Terrebonne in natural sciences. Then, when the time came to choose a university program, physics was at the top of her list, followed closely by medicine. The determining factor? “Comparing the course choices of the two programs, I saw courses in physics that I thought were far too fascinating for me to miss out on this unique opportunity to explore. I couldn’t imagine myself making a living without taking a course in astrophysics or a course in general relativity, or even chaos and nonlinear phenomena. Finally, after a few years in physics, I realized that there was even more to discover than astrophysics, I chose other specialties,” says Ms. Rochette.

The attraction of cooperative internships and a few visits to the Université de Sherbrooke campus as part of the Festival des Harmonies at her high school will guide her to Sherbrooke. “My last criterion was the desire to start my adult life in a different environment, independently,” explains the one who also wore the Vert et Or colours in ultimate frisbee.

Thesis Topic

Attracted to physics by astrophysics, Ms. Rochette ends her university career by directing her research to the field of quantum information, a field where we try to control quantum objects to be able to use them to encode information. More specifically, she is interested in silicon quantum dots.

“What I did in the framework of my doctorate degree was develop and characterize a new architecture to make quantum dots in silicon which give sufficiently convincing performances to consider integrating them into industrial manufacturing processes. It’s a single-layer architecture with separate accumulation grids. To demonstrate its potential, we have demonstrated that it is possible to form highly confined quantum dots, to control valley separation, an important criterion in silicon, and to effectively adjust the tunnel rate between the quantum box and its reservoir. We observed that for these three criteria, the qubits architecture developed within the framework of my research project gave performances comparing advantageously to the state of the art in the matter. Even if we go from a multi-layer quantum dot to a single layer quantum dot,” details Sophie Rochette.

The work doesn’t end there. “I then developed a model to explain certain characteristics that we observed in the stability diagram, namely the experimental measurement which gives us a reading of the number of electrons found in the quantum dot. We observed a particular curvature in the charge transitions in this one. We then had to find the origin of the phenomenon. My model strongly indicates that controlling the tunnel rate with a tank grid, which results from the structure with separate single layer accumulation grids, generates this effect through the accumulation of charges in the tank. It took several months of stubborn work to arrive at a satisfactory version of this semi-empirical model,” notes Ms. Rochette.

Prof. Michel Pioro-Ladrière congratulated his student.“Sophie is an inventor. Her invention is a canvas that will facilitate the manufacturing of the quantum computer. Its impact is international. Indeed, big players in research are now adopting her invention in order to accelerate the development of spin qubits worldwide. Sophie dares to transform the way science is done, by rewarding collaboration instead of competition, and by blowing a wind of change in terms of equity, inclusion and diversity. It is a privilege for me to have accompanied Sophie during this important stage of her university journey and to see her finish her doctorate with panache is one of the highlights of my life as a researcher.”

And for the Future

The future is currently particularly uncertain, and the question arises even more acutely for a graduate student. “The future is a bit vague; the current situation brings a lot of uncertainties. A few avenues are still open to me, and I intend to explore them. In the short term, I would like to be able to apply some of my skills in the effort of resolving the current crisis. In the long term, I want to continue to promote diversity and inclusion in research and play a role in the next technological revolution.”

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