Science that matters: Master’s student researches quantum models of water molecules using computational methods

By Alyana Versolatto
Graduate Recruitment Officer

Nithin Aaron is a theorist at heart, currently studying quantum computing as a Master of Science in Physics (Quantum Information) student at the University of Waterloo. He began to realize that he is a theorist and not an experimentalist (meaning he is more interested in the mathematical aspects of quantum computing and less in the hands-on lab experiments that use the findings of the mathematical work) during his undergrad at McMaster University.

Aaron knew he excelled at math, physics, and chemistry, and particularly enjoyed physics, but it wasn’t until he took an introductory quantum mechanics course in his second year that he discovered quantum computing and was instantly fascinated. This realization led him to focus most of his upper-year electives on math and physics courses and to eventually pursue his education further in graduate school.

After researching graduate programs around the world, it was ultimately the reputation of the Institute for Quantum Computing (IQC) and the excellent fit he found with his supervisor professor Pierre-Nicholas Roy (Tier 1 Canada Research Chair in Quantum Molecular Dynamics), that finalized his decision to come to Waterloo. Aaron is expected to graduate from his master’s program next spring. After that, he plans to pursue a PhD continuing on in the field of quantum many-body physics and to start a career as a computational physicist working on quantum simulation at a company like Pasqal, Xanadu or 1QBit.

What has your experience in the Master of Science in Physics (Quantum Information) program been like so far at Waterloo?

I love IQC and the graduate student communities at Waterloo. IQC has nice perks like coffee, cookie time every day, and pizza at student seminars. They often host social events, as well as interesting colloquiums and public lectures, so there is always something to look forward to outside of my research and coursework.

What is your research focused on?

I am supervised by Dr. Roy, and in general, our research group studies quantum molecular systems using computational methods such as the density matrix renormalization group (DMRG), quantum Monte Carlo (QMC), and generative modeling. I work on a particular type of QMC called path integral Monte Carlo (PIMC) and apply it to study quantum models of water molecules.

A significant component of PIMC is importance sampling, which involves generating samples from a high-dimensional non-trivial probability distribution—and is thus a very difficult task. My research specifically looks at novel techniques for performing this task of importance sampling more efficiently by drawing on physical insights from the quantum systems of interest so that we can simulate larger and more complex systems using fewer computational resources.

What wider implications to academia or industry could your research have?

A postdoctoral fellow in our research group, Tobias Serwatka, recently published a study using DMRG to show that a one-dimensional (1D) chain of water molecules can exhibit a collective phenomenon known as a quantum phase transition, which makes such molecular systems good candidates for quantum materials. What is especially exciting is that we have an abundance of water all around us, so these systems are relatively cheap to physically realize in an experimental lab.

However, while DMRG is a state-of-the-art approach, it is restricted to simulating 1D systems, whereas PIMC does not face this same limitation. Therefore, my research will allow us to simulate analogous 2D and 3D lattices of water molecules, and hopefully observe similar quantum many-body phenomena in these systems as well, leading to more applications in quantum information devices.

What is the working relationship like with your supervisor?

I love working with Dr. Roy. He has such a vast knowledge of my research field and never runs out of ideas of what to work on next. He is also very understanding when I have other things going on in life, whether it be coursework, deadlines, or personal matters—he never makes me feel overwhelmed or pressured to produce results. I always feel secure asking him questions about anything because he is very approachable, is happy to help, and doesn’t consider any question to be ‘dumb.’ He is also just an all-around fun person to hang out with and occasionally hosts the group for jam sessions or karaoke!

How do you spend your time outside of your studies, and what do you enjoy about living in the Waterloo Region?

For both my physical and mental health I enjoy going to the campus gym at Columbia Icefield and running on the Laurel Trail through Waterloo Park past the Perimeter Institute. I also watch a lot of TV and listen to quite a few podcasts, with my favourite TV show being Scrubs and my favourite podcast being Fake Doctors, Real Friends with Zach and Donald (the Scrubs rewatch podcast). I also enjoy socializing at the Grad House on campus and many of the cool bars in uptown Waterloo. A goal of mine is to try out all the local craft breweries in the area—there are still a lot of places I have yet to explore!