Thesis Defence: A lucky Friday for Patrick Harvey-Collard

Contrary to popular belief, Friday the 13th was lucky for Patrick Harvey-Collard. On April 13, he defended his thesis before his peers at Université de Sherbrooke. Patrick was feeling positive and confident as he flew to Sherbrooke for the occasion. “I feel good about my thesis defence. I’m going to take the opportunity to see my friends and family and hang out with people at Université de Sherbrooke.”

From Magog to Albuquerque

An outdoor and wide-open-space enthusiast, the Magog native went to New Mexico in 2013 to conduct his doctoral research at Sandia National Laboratories as a student at Université de Sherbrooke under the supervision of Professor Michel Pioro-Ladrière: “Since Sandia doesn’t grant degrees, students must absolutely be sponsored by a university to ensure their academic requirements are met. It’s a partnership. They handle the entire research side: facilities, devices, most of the laboratory resources. And the thesis advisor, through scientific discussions, helps guide the research and solve certain problems. He makes sure my research project is valid from a university criteria perspective.” Patrick adds: “My advisor at Sandia is Malcolm Carroll. Two advisors can mean a lot of feedback. But the advantage is that you learn more and can combine different expertise. Professor Pioro-Ladrière helped us take a step back from our research and maximize its impact.”

“It was Professor Pioro-Ladrière who put me in touch with Sandia National Labs when I finished my master’s degree. He knew my advisor there and they had discussed the possibility of working together a few times. Another student and I were actually among the first to formalize the collaboration. They also sent microchips to Sherbrooke so that students in my thesis advisor’s group could work on them. During this time, there were two kinds of strong collaborations.”

As Professor Pioro-Ladrière points out, the partnership between the two institutions is of great importance: “Patrick’s thesis demonstrates the strength of collaborative research. On the one hand, it’s wonderful to be able to count on Sandia National Laboratories to manufacture the semiconductor qubits studied at the Institut quantique. On the other hand, Sandia National Laboratories benefits from the Institut quantique’s exceptional expertise as well as that of high-calibre students like Patrick.”

New spin qubits

Patrick’s doctoral research work focuses on spin readout, coherent coupling between a quantum dot and a donor, and spin-orbit effects in quantum dots in silicon. His research has demonstrated experimentally two new ways of controlling, and one new way of reading, spin qubits. Silicon is the semiconductor material used to manufacture processors and other modern electronic devices.

There are several ways to encode information in spins inside semiconductors. The best way to encode the information is with the nuclear spin of a donor. “A donor is essentially a different atom that has an extra electron that can be used to interact with the spin of the atomic nucleus.” Nuclear spins are the best solid-state qubits in terms of reliability. The error rates are extremely low. As they are atomic systems, it is, however, difficult to couple them directly. This requires a nearly atomic level of manufacturing and precision, which is a major challenge. Researchers are now able to make one, but they are not able to make two or three positioned next to each other and have them communicate together. One of Patrick’s goals was to couple a donor to a quantum dot, with the ultimate goal of coupling donor nuclear spins together in a quantum computer. Among other things, this led him to publish a paper in Nature Communicationsentitled “Coherent coupling between a quantum dot and a donor in silicon.”

“This article is my masterpiece, so to speak. It’s the first step in a large system that can be used to build a quantum computer. We’re showing that the hybrid system between the quantum dot and the donor forms, in itself, a qubit that is driven by certain interactions, but that it is also, in a broader perspective, a way to interact with these nuclear spins without atomically-precise fabrication. We can compensate for the uncertainty associated with the position of the donor with the quantum dot. This is the first time that someone has electrically performed coherent quantum control between a donor and an object external to the donor.”

Throughout his research journey, Patrick came up against challenges that quickly turned into opportunities: “I developed a spin readout technique that had been put forth in the past and I brought it to a new level. I showed that you can get never before attained performances. Currently, we have the highest state of the art for the lowest spin readout error rates. It’s a readout method that applies to a large family of spin qubits and that is, in my opinion, the future of the field. The proof is that the best groups in the world have started using it.”

Patrick went on to work for about a year on spin-orbit interactions in quantum dots. This aspect of his work is lesser known in Sherbrooke.

His biggest challenge? “I think my doctorate went well. The main thing is to set enabling goals that will help you achieve your ultimate goal. My spin readout method is one example. In a sense, our goal is to figure out the rules,” Patrick says. “We don’t make the rules of physics and nature—we just discover them. There is a fundamental reason that makes it work or not. We have to overcome the technical obstacles through creativity and pick our battles.”

A bright future

His philosophy, as a physicist and scientist, is that he ought to view the world as his playground: “Basically, I would like to work as a researcher or a professor at an institution or a large company. It depends what opportunities become available to me. My goal is to choose a place that can provide a good balance between research and living environment. The challenge with this field is that high-level science is international. There are offers and opportunities out there, but you have to consider the whole world.”

Patrick will be leaving the United States for the Netherlands in July 2018. He will conduct his postdoctoral studies at Delft University of Technology. Still in the field of quantum information science, his research topic will essentially focus on spin qubits coupled with superconducting resonators. This will allow him to develop a new area of expertise and add another feather to his hat. “The Institut quantique has already collaborated with this group on this project!” After nearly five years in Albuquerque, an unexplored gem for outdoor sports, Patrick is feeling nostalgic and can definitely say that this city has become like home to him.