Quantum Physics and Gravity Meet in New Assistant Professor's Research

Two landmark achievements of 20th century physics remain stubbornly isolated, despite decades of attempts by scientists to bring them together.

On their own, they’ve been wildly successful. General relativity—Einstein’s grand theory of gravity—fused space and time into a single entity. It birthed the global positioning system and forever changed our conception of the cosmos. Quantum physics, the theory that governs the microscopic realm, powered the engines of the digital revolution, and it’s lighting the way to a new paradigm in computing.

But the two fields have largely been marooned on parallel tracks, rarely intersecting because they seem to describe such disparate domains of reality. “When electricity flows through a circuit, gravity is there,” says Brian Swingle, an assistant professor of physics at the University of Maryland and the newest fellow of the Joint Center for Quantum Information and Computer Science (QuICS). “We just don’t usually need it to describe the physics, so we ignore it.”

That might be fine for the physics of electrical circuits, Swingle says, but scientists expect a unified picture to emerge for the highest-energy, densest material in the universe—a picture in which quantum physics and gravity contribute on equal footing. Swingle, who arrived at UMD this past summer, is part of a vanguard of physicists exploring the connections between these two fields. His work blends quantum information and condensed matter physics with a pinch of gravity, and it’s unearthing curious connections between some of the most eye-catching phenomena that modern physics has on offer—things like quantum entanglement and black holes.

He hopes to expand on this work at Maryland and foster more collaboration between experts in all of these fields. “I think UMD has a lot of great resources, and there’s an opportunity now for new connections to be forged,” Swingle says. “That’s definitely one of the things that really excites me.”

Swingle’s interest in physics was kindled as a teenager, when a set of mysterious symbols captured his imagination. “Senior year of high school I somehow got interested in Maxwell’s equations,” he says, recounting his first contact with the four equations that are the distillation all of the 19th century’s knowledge about electricity and magnetism. “There was this mysterious picture with upside down triangles, which looked like gobbledygook, and it seemed really interesting to me. I’ve sort of been hooked ever since.”

He pursued a physics degree as an undergraduate at Georgia Tech in Atlanta, where he got an early start in research, writing software to simulate the behavior of many interacting particles and spending a summer working as a research assistant at the University of Washington.

He arrived at MIT for graduate school in 2005 with a loose plan to study condensed matter physics. But some early projects didn’t work out. “I thought about switching to neuroscience,” Swingle says. “I was thinking of working on birdsong. I had a general interest in information networks and higher organization.”

But his neuroscience career also stalled, and eventually he ended up back in condensed matter physics working with Xiao-Gang Wen, a luminary in the field. Wen asked Swingle to look into a problem involving quantum entanglement, the curiously strong connection that two quantum objects can share, and something clicked. Swingle became fascinated with entanglement, calculating the entanglement properties of a variety of quantum systems. “I was looking for some kind of picture,” he says, “but I didn’t really know what it was.”

That all changed when he took a class in string theory, the theoretical effort to recast all of modern physics in the language of tiny vibrating strings. String theory made one of the earliest attempts to shoehorn gravity into quantum physics, and over the course of several decades string theorists discovered some interesting relationships between the two. One such connection was a duality between quantum physics playing out in a particular universe and a theory of gravity in a universe with one extra dimension.

Swingle explains the gist of that relationship using a round table. Imagine that the table’s edge—a circle that wraps its perimeter—is a one-dimensional universe with a bunch of interacting quantum systems. It turns out that picking a particular quantum state for this encompassing ring limits what can happen in the interior—the tabletop itself—and vice versa. The truly strange thing is that the tabletop ends up endowed with gravity, but it’s now a theory of gravity in two dimensions. “The question you can kind of ask is ‘Where does the extra dimension come from?’” Swingle says.

It’s a lot of abstract math that need not have much to do with our universe, but Swingle discovered a particular way in which this abstraction becomes real. “I started to see these connections,” Swingle says. “It was starting to gel in an interesting way.”

Tensor networks—graphical webs that can represent the complicated states of interacting quantum systems—provided the key ingredient. Drawing the tensor network of a quantum system living on the edge of a table turned out to be a picture of a theory of gravity inside, a discrete snapshot of the fabric of spacetime on the tabletop. It was a simple theory of quantum gravity, albeit one that does not describe our universe. “Quantum gravity in any spacetime is sufficiently mysterious and sufficiently poorly understood that it's worth understanding even a toy case,” Swingle says.

Since his pioneering result, Swingle has continued to develop the relationship between quantum entanglement—depicted via hierarchical webs of tensor networks—and geometry, and has recently been thinking about the role complexity and computation play in all of it. A recent paper with several collaborators demonstrated a precise mathematical connection between the complexity of a quantum state and the geometry of its dual theory of gravity. It’s part of a body of work that is continuing to shift physicists’ perspectives on quantum gravity. “The old slogan used to be that entanglement was the fabric of spacetime,” Swingle says. “Now maybe it’s more general. Maybe now we think of spacetime itself as a computational history of some process—the picture of the quantum circuit that prepares the quantum state, something like that.”

Now, as an assistant professor at UMD, Swingle hopes to continue research along these lines, perhaps bringing more quantum information tools into the fray. He is also a co-principal investigator for the “It from Qubit” collaboration launched by the Simons Foundation. The name is a play on “it from bit,” a phrase coined by physicist John Archibald Wheeler that underscored the significance of information to the bedrock upon which reality sits. “Of course, information is quantum mechanical, since the world is quantum mechanical,” Swingle says. “Somehow that’s an important ingredient in the story—the quantum-ness is really important.”

Swingle encourages any students interested in learning more about his research to contact him directly or stop by his weekly group meeting, which is typically held on Thursdays at 5 p.m. in PSC 3150.

—Story by Chris Cesare

Congressional Hearing Highlights Need for Quantum Technology Initiative

Credit: E. Edwards/JQICredit: E. Edwards/JQI

On October 24, 2017, two Fellows of the Joint Quantum Institute and the Joint Center for Quantum Information and Computer Science were among those that testified during a joint congressional committee hearing on the topic of American Leadership in Quantum Technology.

Carl Williams and Christopher Monroe attended as expert panelists, reading prepared statements and answering questions from committee members. Williams, who is also the deputy director of the Physical Measurement Laboratory at the National Institute of Standards and Technology (NIST), provided testimony about quantum research at NIST. Monroe—a Distinguished University Professor of Physics at the University of Maryland (UMD) and a co-founder and chief scientist at UMD-based startup IonQ, Inc—advocated for a National Quantum Initiative in his testimony. Both shared their perspectives on the path toward industry’s adoption of this emerging new technology.

The hearing focused on the status of quantum research in the US. Two panels with a total of six experts from government, industry, academia, and national laboratories testified. The witnesses emphasized that quantum information science will play a critical role in future advanced computing and secure communications. They also noted potential applications related to chemistry, medicine, artificial intelligence, and even space exploration.

In answering questions about the maturity of quantum information research, participants cited both Monroe’s and IBM’s small-scale quantum devices. According to panelists, commercialization of quantum technology is an imminent reality, rather than a futuristic goal. Participants discussed the global impact that industrial quantum science will have, noting that governments worldwide are investing in large-scale quantum research. China, Australia and Europe, in particular, are beginning to pour massive resources into funding quantum research.

Quantum at Maryland

UMD’s flagship College Park campus is home to a thriving quantum enterprise that is actively producing a competitive workforce, delivering innovative research, and attracting a network of strategic partners. With more than 175 scientists on-site and countless collaborations within a vast global research network, quantum programs at Maryland are leading the charge toward a quantum future.

  • The Joint Quantum Institute (JQI), founded in 2006, is a physics research partnership with NIST and the Laboratory for Physical Sciences dedicated to intensely studying quantum science.

  • A quantum-focused NSF Physics Frontier Center was first awarded to UMD in 2008 and renewed in 2014. This is a prestigious designation that promotes collaborative exploration of challenging but highly promising research areas.
  • UMD enjoys vital relationships with industrial and government-laboratory efforts in quantum computing, such as Microsoft, Northrop-Grumman, Sandia National Laboratories, the Army Research Laboratory, Booz-Allen-Hamilton, and the startup IonQ, Inc. Many UMD graduates have taken positions at these places. 

MEDIA CONTACT

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Ravi Kuchimanchi Awarded Sakharov Prize

Alumnus Ravi Kuchimanchi (Ph.D., 1995) has been awarded the 2018 Andrei Sakharov Prize of the American Physical Society "for his continued research in physics while simultaneously advocating for global policies that reflect science; for leading sustainable development, human rights, and social justice efforts; and for creating a vibrant international volunteer movement that learns from, works with, and empowers communities in India."

The Sakharov Prize, established to recognize outstanding leadership and/or achievements of scientists in upholding human rights, is named for the Russian nuclear physicist-turned-activist who won the 1975 Nobel Peace Prize for his advocacy of freedom, disarmament and human rights.

Dr. Kuchimanchi founded Association for India’s Development (AID) while a UMD graduate student. In 2012, he was named the International Alumnus of the Year by the College of Computer, Mathmatical and Natural Sciences. His life was dramatized in the move Swades.

Five UMD Physicists Elected APS Fellows

Michelle Girvan, Wolfgang Losert, Johnpierre PaglioneEdo Waks and Jake Taylor have been elected Fellows of the American Physical Society.

Prof. Girvan was cited for seminal contributions to the nonlinear and statistical physics of complex networks, including characterization of network structures and dynamics, and interdisciplinary applications.

She received her Ph.D. in physics from Cornell University, and joined the Department of Physics in 2007, after a postdoctoral appointment at the Santa Fe Institute. Prof. Girvan was a visitor at the Institute for Advanced Study from 2008-09, and in 2017 received the Richard A. Ferrell Distinguished Faculty Fellowship in the Department of Physics. She is a member of the Institute for Physical Science and Technology, and the Director of the COMBINE (Computation and Mathematics for Biological Networks) program.

Prof. Losert was cited for his imaginative studies of complex living systems, and for numerous contributions to understanding dynamical properties of complex systems at the convergence of physics, materials science, and biology.

Prof. Losert holds a Ph.D. in physics from the City College of the City University of New York, and joined UMD in 2000 after appointments at Haverford College. He has served as director of the UMD Biophysics graduate program and is currently the director of the UMD-NCI Partnership for Cancer Technology and the Associate Dean for Faculty Affairs, Graduate Education and Research in the College of Mathematical and Natural Sciences. In 2006, he received the Richard A. Ferrell Distinguished Faculty Fellowship.

Prof. Paglione was cited for experimental contributions to the understanding of strongly correlated and topological electronic materials through the synthesis and investigation of heavy fermion compounds, unconventional superconductors and topological materials.

Prof. Paglione, who received his Ph.D. in experimental condensed matter physics from the University of Toronto, joined UMD in 2008. He is the recipient of a National Postdoctoral Fellowship Award from the Natural Sciences and Engineering Council of Canada, a Materials Synthesis Investigator Award from the Gordon and Betty Moore Foundation, a DOE Early Career Award, the 2012 Richard A. Ferrell Distinguished Faculty Fellowship, and an NSF Career Award. He is currently the director of the Center for Nanophysics and Advanced Materials and is an Associate Fellow of the Canadian Institute for Advanced Research (CIFAR) Quantum Materials program. 

Prof. Waks was cited for significantly advancing the field of quantum photonics and for developing new concepts to strongly interact solid-state quantum emitters with nanophotonic components.

He received his Ph.D. in electrical engineering from Stanford University, and after a postdoctoral appointment there, joined the UMD Department of Electrical and Computer Engineering in 2008. He accepted a joint appointment with the Department of Physics in 2017. Prof. Waks researches nanoscale photonic and semiconductor devices for applications in quantum computation, communication, and sensing. He is a Fellow of the Joint Quantum Institute and of the Optical Society of America and is the recipient of a Presidential Early Career Award and an NSF Career Award.

Dr. Taylor was cited for wide ranging contributions in using quantum properties of light and matter towards developing applications ranging from extreme sensitivity sensors and transducers to quantum information processing. 

He received his Ph.D. from Harvard University and was a Pappalardo Fellow at the Massachusetts Institute of Technology before joining the National Institute of Standards and Technology and the Joint Quantum Institute in 2009. He has received a Presidential Early Career Award, a Department of Commerce Silver Medal, a NIST Sigma Xi Young Scientist Award and a C15 Young Scientist Award from the International Union of Pure and Applied Physics. Dr. Taylor is the NIST Co-Director for the Joint Center for Quantum Information and Computer Science. 

In addition. Dr. Surjalal Sharma from the Department of Astronomy was cited for pioneering and sustained contributions to nonlinear dynamical modeling of non-equilibrium phenomena in space physics and to the development of data-enabled science and for his leadership in fostering international collaborations.