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# Peter Rosenberg Brings his Expertise on the Auxiliary-Field Quantum Monte Carlo Method to the IQ as a Post-Doctoral Fellow

Peter Rosenberg

Photo : FournieThe Institut quantique (IQ) welcomed Peter Rosenberg amongst its postdoctoral fellows last November. This experience being his second postdoctoral fellowship, the Long Islander will bring his expertise on the study of many body treatments of topological systems to the IQ. In David Sénéchal’s group, he will apply, amongst other techniques, an auxiliary-field quantum Monte Carlo method to existing complex models developed by IQ professors.

**From Nuclear Physics to Condensed Matter Physics**

During his undergraduate degree at State University at Geneseo, Peter Rosenberg enrolled in a Research Experiences for Undergraduates (REU) program, which provides research experience for undergraduate students for the summer. His research concerned nuclear physics, which led him to start his graduate school in the same field of study at the College of William & Mary.

“What I really liked about my first research experience was that they had me helping with a small computer program in the context of nuclear physics. Solving a physics problem with the help of a computer was very appealing to me. That was the beginning of me heading in the direction of computationally oriented physics. As a graduate student, I ended up switching specialties to condensed matter physics, which I did for about seven years, including my first post-doctoral fellowship at the National High Magnetic Field Lab at the Florida State University,” shares Peter.

Indeed, his PhD expertise concerned computational many body physics, as he worked in a condensed matter theory group. His doctoral advisor, Professor [Segway] Chang, had developed many techniques and algorithms to do computational many body calculations, which led Peter to develop a strong expertise in the field: “I learned a particular technique, called the auxiliary-field quantum Monte Carlo method. I was then able to take my expertise to the National High Magnetic Field Laboratory, and I aim to accomplish similar outcomes here at the IQ.”

**Bringing His Expertise to the IQ**

Peter Rosenberg’s post-doctoral fellowship at the IQ is the continuation of his study of many body treatments of topological systems, but for a particular class of models that targets the physics of high-temperature superconductors.

“In Sherbrooke, Professor Louis Taillefer’s group has measured a thermal Hall effect from phonons in high-temperature superconductor materials, which is a fairly interesting observation. In Professor David Sénéchal’s group, in collaboration with Professor André Marie Tremblay, we want to study the [Howard] Model using my technique and attempt some calculations to see if we can observe this thermal Hall effect coming from phonons. It’s a challenging problem: many have tried to solve this model in more than one dimension, but there’s no close formed solution for it. We’re hoping to be able to calculate some quantities that will maybe provide some insight to these experiments,” adds Peter.

The solutions to these types of models with high accuracy methods like Peter’s could be a good way to benchmark other techniques or to cross corroborate different approaches. “If you have a gold standard to treating this particular model, you could then possibly treat something more complicated. Devising a very accurate method to treat a simpler model and hopefully do something more complicated could eventually solve the high-temperature superconductor problem.” And so, indirectly, having a high accuracy treatment of a system that has these topological features and interactions could be forecasted to be useful to quantum computing.

During his graduate studies, Peter published a couple of papers in Physical Review Letters, which study the [Howard] model with spin orbit coupling term using his method, which brought numerically exact results on a model that may be realized soon. Then, during his first post-doctoral fellowship at the National High Magnetic Field Laboratory, he published an article in Physical Review B, regarding superconductivity and these topological systems, which were again treated with the auxiliary-field quantum Monte Carlo method.

“The IQ was an obvious choice for my postdoctoral fellowship since they have a strong reputation in Canada in quantum materials and in quantum information. They also have notable experts not only in high-temperature superconductors, but also in treating model Hamiltonians and computational approaches to them. The position also offers some freedom regarding my research interests and the opportunity to collaborate,” he shares.

**Adapting to a New Environment**

“I will be doing a number of collaborations and side projects. For instance, I’m collaborating with Professor Maxime Charlebois at Trois-Rivières, and others outside the Université de Sherbrooke. I still work with my PhD advisor and with my postdoc advisor, Professor Efstratios Manousakis. I greatly appreciate the collaborations happening at the moment.”

“The adaptation to working from home is easy, but strange. I look forward to being able to be on the campus regularly and working in an office. On the plus side, we’re used to travelling around to conferences and only attending a seminar when someone comes to the department, but now there is a multiplicity of virtual seminars, which is nice. Once I complete my postdoc, ideally, I would like to be a professor somewhere, or at least mentor graduate students while maintaining some research activity.”

The IQ welcomes you to the team, Peter!