Quantum Entanglements
Adrian Del Maestro has a unique way of explaining exactly what about quantum science captured his attention. He calls it anti-maple syrup. That may not be the most technical description of superfluid helium, but it’s a vivid illustration of how this frictionless phase of matter behaves, and his fascination with such quantum phenomena guides the research program he brought to the physics department this fall as a new professor.
An appreciation for science was woven into Del Maestro’s upbringing in London, Ontario, Canada. His father, Rolando Del Maestro, holds both an MD and a PhD and balanced a neurosurgical practice with a research group studying brain tumors. Though his practice has closed, he’s still active in research as an emeritus professor at McGill University and continues to work with the Brain Tumour Foundation of Canada he co-founded.
"I grew up in a highly academic household," the younger Del Maestro said. "We often had postdocs and scientific visitors staying for extended periods of time in our basement. In fact, my first paper was written together with my father when I was an undergraduate."
Del Maestro always had a penchant for science and math and majored in both at the University of Waterloo. It was during his undergraduate studies that he began focusing on condensed matter. He went on to earn two master’s degrees in physics (one at Waterloo and a second at Yale University) before heading to Harvard University, where his doctoral research centered on a theoretical quantum phase transition between a superconductor and a metal. Among his postdoctoral research appointments was a stint at the Institute for Quantum Matter at Johns Hopkins University.
Understanding the intricate workings of quantum systems—the entanglement of their constituent particles and how those particles behave in the collective—has long intrigued Del Maestro. Some of the most interesting territory is the potential for new, emergent phenomena, where macroscopic behavior isn’t visible at the microscopic level. Among these phenomena are superfluids.
"The one aspect of the quantum world that really got me interested was superfluid helium," Del Maestro explained. "I find the superfluid phase of helium fascinating. This is the only strongly interacting elemental superfluid we know of and it can flow without any viscosity. I like to think of it as the anti-maple syrup."
This "syrup" also shows how the quantum world needn’t necessarily be confined to microscopy.
"We usually think of quantum mechanics applying only to the very small; atoms and molecules, etc.," Del Maestro explained. "But you can cool a coffee mug of helium down to 2 K (-271 C) and the entire thing will undergo a phase transition to a superfluid described by a single macroscopic quantum wavefunction. The idea of understanding and potentially exploiting quantum phenomena on this human-sized scale continues to excite me and motivates a large swath of my work."
Quantum systems, however, come with the thorny issue of having multiple subatomic components and a daunting number of interactions, better known as many-body problems.
"The sheer complexity of quantum-many body systems and the exponential number of microscopic configurations that they can take on is the persistent challenge of our field," Del Maestro said. "Even if we can write down a complete description describing all interactions, we can often only gain insights into the behavior for a few particles or in very special situations."
The rules governing quantum systems can cause headaches for theorists. This is especially true for fermionic wavefunctions (electrons, or say Helium-3) where interactions and motion can cause the emergence of negative signs that prevent simulation on classical computers. Still, Del Maestro said that in some cases they may be able to find techniques or algorithms to work around this "sign" problem.
"Searching for such tricks is an important part of what we do and finding them immediately opens up new areas of research and potentially a path towards novel technologies," he said. "Pursuing this research has led to the development of tools that utilize high performance computers to simulate the quantum world. This is the ultimate theoretical platform where we can search for the answers to curiosity driven questions."
Before joining UT Del Maestro spent nine years on the physics faculty at the University of Vermont (UVM). He also served two years as the director of the Vermont Advanced Computing Core (VACC), which provides large-scale advanced computing resources to UVM researchers. That experience, coupled with his own research, made clear to him the critical role these resources play in contemporary science.
"Access to high performance computing and all the supporting advanced cyberinfrastructure is as important to modern science as brick and mortar infrastructure," like labs and fume hoods, he said. "Removing limits on computing access allows researchers to attack problems that were previously deemed ‘too difficult’ and more importantly, engage in rapid feedback loops that advance science in new and unpredictable ways."
As the VACC director he saw firsthand how high-performance computing is an area where researchers "walk-the-walk" of multi-disciplinarity. Tools can be shared quickly between different research areas, especially with open source software. His experience with advanced computing and shared expertise fits well with Del Maestro’s role in UT’s cluster in quantum materials, part of a university initiative to make strategic hires in areas that will benefit Tennessee and the wider world.
"The quantum materials cluster intends to attract a critical mass of researchers that can work closely together to solve broad and deep challenges on how we can leverage quantum mechanics and materials science to build future technologies in aid of societal goals," he said. "UT is the perfect place for this endeavor, with a very deep bench of existing expertise in this area, and the support from the administration in realizing the clusters vision has been impressive."
Del Maestro’s position is a joint appointment with Min H. Kao Department of Electrical Engineering and Computer Science, which is a natural fit given his computing background, and he is actively engaged with his colleagues there. He’s also had many discussions with Physics Professor George Siopsis about the Appalachian Quantum Initiative, an interdisciplinary team devoted to leveraging university and partner strengths in quantum computing and supercomputing.
As computing becomes more sophisticated, so too do possibilities for solving quantum puzzles.
"I try to ask big questions and then focus on the parts that are standing in the way of an answer," Del Maestro said.
One of his current obsessions is that in quantum mechanics, like things are indistinguishable.
"There is no experiment that you can perform to distinguish between two electrons," he said. "So a natural question arises, can we do something with this non-classical facet of the world? Is there useful entanglement encoded in the many-body phases of quantum matter made up of identical constituents? If so, can we measure it? Can it be tuned and optimized? Can we extract it? Following my nose down paths like this yields more research problems than I have time to answer."
When he does set out to tackle a problem, Del Maestro starts with a literature review to assess the state of the field and see what’s already been tried.
"The hope is that one of the tools in our arsenal can be applied to the problem and that our experiences can add something to the field," he said.
That was the case with work his group published in Nature Physics a few years back about their studies on entanglement in superfluid helium.
"While people had previously studied the area law (the fact that entanglement entropy has fundamentally different behavior than thermodynamic entropy) in simple models of magnetism, we demonstrated this behavior in experimentally realizable quantum liquid," he explained. "The connections between this entropy ‘area law’ and the one made famous for black holes by Stephen Hawking led to the paper receiving a lot of interest" (including an Altmetric score of 202, putting it in the top five percent of all measured research).
As firm believers in open science, his group made all code and data from the project available to other scientists. It has since been used for research outside their involvement, something Del Maestro calls "a very exciting outcome in terms of the famous ideas of Eric Raymond’s Cathedral and the Bazaar: ‘given enough eyeballs, all bugs are shallow.’"
This idea of sharing tools and knowledge will be front and center for the spring 2021 term, when Del Maestro will teach a new course called "Introduction to Machine Learning for Scientists."
"I love teaching computational physics because it is amazing to see the empowerment of junior physicists when you provide them with the tools of high-performance scientific computing," he said. "I’m excited to convey how the tools of artificial intelligence can be applied to modern problems in physics."
He hopes to add more students to his research group, which includes graduate student Emanuel Casiano-Diaz (who came from UVM) and postdoc Dr. Hatem Barghathi.
Not everything in life, of course, is quantum entanglement, and Del Maestro has plenty of interests outside the world of algorithms. An avid sports fan, he’s on the lookout for a post-COVID lacrosse team to join. He insists, however, that his wife Caitlin, a project manager in public health education, is better at all sports than he is ("You should see her pull the ball to right field"). Eventually he’d like to translate his love of sports into a new course like one he developed for freshmen at UVM, where students learned how Bob Beamon held the long jump world record for 23 years and why a curve ball curves or a knuckle ball dances.
He and Caitlin also have a family with "two amazing daughters and an American Staffordshire terrier named Cooper (yes, after BCS theory)."
Even though moving to a new university in the middle of pandemic can be a formidable undertaking, Del Maestro is optimistic about what the future holds.
"I’m incredibly excited about the opportunity to move my research and teaching to UT and interact with the amazing people in Physics and Astronomy and the Min H. Kao Department of Electrical Engineering and Computer Science," he said. "Everyone has been so welcoming and supportive thus far and I can’t wait to see how the Quantum Materials for Future Technologies cluster positions the University of Tennessee as a global leader in the field."