Spectrum - SPRING 2022
The Department of Physics at the University of Illinois at Urbana-Champaign is known for its collegial style of research—the “Urbana style”—that often involves collaborations across research areas and among theoretical and experimental physicists. Here is an inside glimpse of what some of our leading physicists are working on.
Astrophysics, Relativity, and Cosmology
Physics Education Research
Theoretical Condensed Matter Physics
My work focuses on studying the most violent and extreme physical phenomena in the universe. Black holes are the densest objects in nature, possessing such strong gravity that not even light can escape their interior. Neutron stars are less dense, but the pressure and densities in their cores are still so extreme that the building blocks of matter—neutrons and protons—may dissolve into a soup of quarks.
Both of these “compact objects” are unavoidable predictions of Einstein’s theory of general relativity. When these compact objects collide with each other, their collision releases tremendous amounts of energy in just milliseconds, outshining all the stars in the universe put together for a short moment. How is it then that we don’t see these collisions with the naked eye? The reason is that the energy released is not contained in light waves, but rather in gravitational waves—ripples in the very fabric of space and time. The Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors in the United States and the Virgo interferometer detector in Italy have already observed over 90 such gravitational waves—the first detection in 2015 earned the 2017 Nobel Prize in Physics.
My group performs both analytic calculations and computer simulations on high-performance clusters to understand the details of these compact-object collisions and to search for new physics in gravitational wave data. Specifically, we construct models within Einstein’s theory and in its quantum gravitational extensions that we then compare to data through Bayesian analysis to pull physics out of the noise. What are the properties of matter in the cores of neutron stars? What are dark matter and dark energy? Does Einstein’s theory correctly predict nature when black holes collide and gravity waves? These are but some of the questions that we tackle in the gravity theory group.
Research in the Yunes group is supported by the National Science Foundation (NSF) Windows of the Universe Astrophysics Theory Program under Grant Nos 2009268 and 2007936, the NSF Gravitational Physics Program under Grant No. PHY-2207650; by a NASA Research Opportunities in Space and Earth Sciences, Astrophysics Theory Program Grant No. 80NSSC22K0806; and by a Simons Foundation Targeted Award in MPS Grant No. 896696. The findings presented are those of the researcher and not necessarily those of the funding agencies.
My group’s research is at the interface of biology and physics. Biology is often perceived as complicated and unpredictable, but we try to discover the generalizable principles underlying the complexity by using physics-inspired methods and analyses. More specifically, we develop advanced instruments that offer higher precision and sensitivity in measurements and make predictable and testable theoretical models.
One of the problems that we are interested in is transcription. Transcription is a process whereby genetic information on DNA is copied into a form of a polymer called messenger RNA, which serves as a template for protein synthesis. Transcription involves many cellular factors, but the primary player is an RNA polymerase, which is a molecular motor that moves along the DNA in one direction. Inside cells, multiple RNAPs run on the DNA, just like cars running on a highway. If the RNAPs were actually like cars, they would influence each other’s motion only upon physical collision. However, we found that the RNAPs can influence each other’s motion from a far distance, without physical contact, by affecting mechanical stress on the DNA that they share. While we are studying the biological implications of this interaction, we are also looking at the physical properties of DNA that allow for this long-distance “communication” between moving motor proteins. One possibility is that the mechanical stress created by an RNAP is transmitted through DNA, just like electricity on a wire. We are trying to build an instrument that can manipulate DNA’s mechanical stress and measure its dynamics. All living cells contain DNA as genetic material, and its sequence (genetic code) has been a primary focus in biology. Our study will help illuminate the hidden nature of DNA and will give us a better understanding of the biological capacity that this fundamental molecule of life carries.
Work in the Kim research group is supported by the Searle Scholars Program and by the National Institutes of Health under Grant No. R35GM143203. The findings presented are those of the researcher and not necessarily those of the funding agencies.
How can we help physics students succeed? Besides the physics topics listed in the course syllabus, successful students learn a wealth of strategies for thinking about and learning physics, such as connecting physical and mathematical reasoning, anchoring one’s understanding in a small set of fundamental principles, and building coherence among different ideas. However, other students may struggle to recognize and pick up these ways of thinking in their courses, making succeeding in physics class a challenging prospect. My research group works to formalize our understanding of these strategies that constitute physics expertise and to provide equitable opportunities for learning them in physics class.
Our approach to physics education combines basic research on the fundamental mechanisms of learning with course design and implementation. Our work relies on disciplinary physics knowledge as well as methods and theories from other fields, such as education, psychology, and cognitive science. We build cognitive models of physics expertise by studying the problem-solving and reasoning behaviors of students and experts through interviews, classroom observations, and experiments. My group specializes in developing models of how one’s knowledge and epistemological beliefs (or beliefs about what it means to do physics) interact to produce physical reasoning and insights.
These models of physics expertise motivate the development and testing of new principles for teaching and assessment. In line with the long history of educational innovation at Illinois Physics, these principles get implemented into our courses, where they can be tested and refined. Current efforts focused on helping students build coherence among physical and mathematical ideas are being implemented in PHYS 100, a course developed at UIUC to prepare students for success in the introductory physics course sequence. In this way the research is having a direct and immediate impact on our students’ educational experiences.
This work in the Kuo research group is supported by the National Science Foundation under Grant No. 2100040 and by the University of Illinois Grainger College of Engineering Strategic Instructional Innovations Program. The findings presented are those of the researcher and not necessarily those of the funding agencies.
My group works in condensed matter systems involving large numbers of strongly interacting degrees of freedom and having strong effects of quantum mechanics. We use the framework of quantum field theory to study and explain the emergent behavior of high-temperature superconductors and topological phases of matter.
I showed that strongly correlated electronic systems become spontaneously organized into electronic liquid-crystal phases. Three features of these phases, which break spatial symmetries to different degrees and are often superconducting, are that the orders are closely intertwined, have comparable strengths, and have similar critical temperatures. A good example of this is observed in the electron nematic phases in systems ranging from high-temperature superconductors to two-dimensional electron fluids in high magnetic fields.
Recently, I showed that a novel form of superconductivity, the pair-density wave, is the natural explanation of many intriguing experiments seen in a family of high-temperature superconductors. The big challenges now are to determine the role of the pair-density wave in the phase diagram of these superconductors and, more broadly, to understand the microscopic origins of intertwined orders. These projects require strong collaborations with UIUC experimentalists.
Topological phases are quantum states of matter that do not break any symmetry and have large-scale quantum entanglement. More specifically, topological phases are ground states that exhibit a degeneracy determined by the topology of the space in which they live. These states are observed in two-dimensional electron fluids in high magnetic fields that exhibit the fractional quantum Hall effect. Strikingly, the excitations of these topological fluids are quantum vortices that carry fractional charge and fractional statistics, intermediate between fermions and bosons. These vortices constitute a natural platform for topological qubits.
This area of research is characterized by strong and mutually nurturing interactions among condensed matter, high energy physics, and mathematics. In my group, we construct effective field theories for fractionalized phases, particularly in quantum Hall fluids. We are developing models of how to interact with and control fractionalized excitations and are developing models representing three-dimensional fractionalized states.
Work in the Fradkin group is supported by the National Science Foundation under Grant No. DMR 1725401. The findings presented are those of the researcher and not necessarily those of the funding agency.