Revealing new insights into quantum system interactions
IQC researchers develop theoretical framework and experimental tools to better understand how quantum systems interact
By Naomi Grosman
Researchers at the Institute for Quantum Computing (IQC) at the University of Waterloo have explored how quantum systems interact with their environments, revealing insights that could enhance future quantum computing applications.
Quantum systems — physical systems that follow the rules of quantum mechanics — all interact with their environments, but that interaction ranges from weak, minimal interference to strong interactions so impactful that the system and environment start affecting each other. Understanding the distinction can help scientists predict quantum system behaviour, potentially leading to a better understanding of fundamental science and improvements to quantum computing systems.
But so far, the transition from weak to strong has been very difficult to pinpoint.
New research led by Dr. Adrian Lupascu, IQC faculty and professor in the Department of Physics and Astronomy, members of his research group and collaborators has now better described the transition and built the theoretical framework and experimental tools to do so.
“Sometimes making progress in quantum information requires advancing certain limits of technology, such as increasing the size of a quantum system or improving its control. But our research is a different category of progress; we highlighted that there is something interesting happening in the transition from weak to strong coupling and found a physical implementation where we can explore this intermediate regime which is not something that was known or had been achieved before. We can now see where this crossover happens which gives more motivation and input to do future theoretical work.”
- Dr. Adrian Lupascu, IQC faculty and professor in the Department of Physics and Astronomy
From left to right, Adrian Lupascu and IQC graduate students Noah Janzen and Sean Dougherty at the Superconducting Quantum Devices Group lab at IQC
From left to right, Adrian Lupascu and IQC graduate students Noah Janzen and Sean Dougherty at the Superconducting Quantum Devices Group lab at IQC
From left to right, Adrian Lupascu and IQC graduate students Noah Janzen and Sean Dougherty at the Superconducting Quantum Devices Group lab at IQC
From left to right, Adrian Lupascu and IQC graduate students Noah Janzen and Sean Dougherty at the Superconducting Quantum Devices Group lab at IQC
From left to right, Adrian Lupascu and IQC graduate students Noah Janzen and Sean Dougherty at the Superconducting Quantum Devices Group lab at IQC
The Waterloo team designed a superconducting single quantum qubit and realized a device based on this design at Massachusetts Institute of Technology’s Lincoln Lab. The qubit design included a feature to allow adjusting the interaction between an atom and its environment from weak to strong — like turning a knob. This allowed the team to observe the transition, providing new insights into the complex physics involved.
Two main authors of the report, Dr. Robbyn Trappen and IQC alumni Dr. Xi Dai (PhD ‘22), collaborated on theory and implementation of the research. Trappen, who was a post doc at IQC while conducting this research, was responsible for running the experimental setup at MIT and coordination of experimental planning. Dai, then a graduate student, was involved in experimental work, contributing to the design of scripts and collaborating on data acquisition and analysis, and a detailed theoretical analysis following the completion of the experiment.
Trappen says the results from this experiment will be important in understanding the behaviour of quantum bits in a larger quantum processor, such as a quantum annealer, which is a specific type of quantum computer used to solve optimization problems.
“We are examining the qubit’s performance in situations very relevant to what it would encounter as part of a larger processer. Other researchers or companies have quantum annealers, but we are exploring an angle that isn’t usually looked at. It uses the same principles but the problems ours can solve is different and there are still questions to be answered how the future of quantum annealing will play out.”
- Dr. Robbyn Trappen, past IQC postdoc
Dai says it is commonly understood that quantum processors should be isolated to preserve their quantum properties, but complete isolation is ultimately unattainable.
“You need to be able to control the system and that always introduces some interaction with the environment. Instead of trying to isolate maybe the first step is to understand what the environment does to the system, which is what we did. The next step is we can maybe engineer the environment in a certain way that steers its effect to a direction we want.”
- Dr. Xi Dai, IQC alumni (PhD ‘22)
The work was part of a large quantum annealing program sponsored by Intelligence Advanced Research Projects Activity (IARPA) and Defense Advanced Research Projects Agency (DARPA). In addition to contributors from University of Waterloo, collaboration included researchers from MIT, Lincoln Lab, Northrop Grumman and University of Southern California.
The paper 'Dissipative Landau-Zener tunneling in the crossover regime from weak to strong environment coupling' was published in Nature Communications in January.
(All images were taken at Lupascu’s Superconducting Quantum Devices Group lab at IQC, University of Waterloo.)