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.

# Spectrum - FALL 2022

###### The Department of Physics at the University of Illinois Urbana-Champaign is known for its long history of collaborative research—the “Urbana style of physics”—that frequently reaches across research areas and involves close coordination between theoretical and experimental physicists. Here is an inside glimpse of what some of our physicists are working on.

ANTONIOS TSOKAROS

Astrophysics, Relativity, and Cosmology**KATIE ANSELL**

Physics Education Research

DEKRA ALMAALOL

Theoretical Nuclear Physics

LAIMEI NIE

Theoretical Condensed Matter Physics

**ANTONIOS TSOKAROS**

When two neutron stars orbit each other, they gradually spiral inward because of gravitational radiation and finally merge in a spectacular collision. For the first time in history, on August 17, 2017, such a binary neutron star merger was observed at both gravitational and electromagnetic observatories, marking the advent of so-called “multi-messenger” astronomy.

My research focuses on understanding such cosmic phenomena and more generally on the physics and mathematics of strongly gravitating systems. This area of research involves general relativity, relativistic hydrodynamics, and magnetohydrodynamics, as well as nonlinear partial differential equations. Some of the topics my group is working on include the inspiral and coalescence of compact binaries (binary black holes, binary neutron stars, or black hole-neutron stars); the generation of gravitational waves from merging binaries and other promising astrophysical sources and their counterpart electromagnetic and neutrino signals; the effect of the neutron star equation of state on the merger remnant; and the stability of rotating, magnetized neutron stars. Einstein’s theory of gravity underlies all these problems—it’s the stage where the various actors play and the drama unfolds.

In my research, numerical modeling is key to making quantitative predictions. From the calculation of a binary neutron star in a circular orbit to its merger and the subsequent launching of a relativistic jet, large-scale computer simulations are required. My group has developed state-of-the art codes for modeling compact objects—some for the first time. These models have been used by many groups around the world to make concrete predictions on a large number of scenarios, including the neutron star maximum mass, the premerger neutron star’s spin, and the fate of the merger remnant for the event observed in 2017.

*Antonios Tsokaros is an NCSA Faculty Fellow and a member of the Relativity Group at Illinois Physics.*

**KATIE ANSELL**

We often talk about classrooms as places where classes are held, but the concept of classroom is incomplete without the participation of teachers and students. My work in physics education and physics education research focuses on bringing students in as central contributors to the learning space of the classroom. The field and subtopics of physics education research are broad, and the work I do is best classified as “action research”—which means, I draw on a rich body of cognitive science and education literature to inform changes in the courses I teach and then I assess student outcomes.

In 2016 my mentor and I began changing the introductory physics laboratories at Illinois to a new curriculum that invites creativity and that trusts students to learn from their experiences to develop a rich, adaptive form of expertise. Individual and group tasks in this format not only develop students’ technical skills, they also require innovation and decision-making. Our students begin the semester with simple tasks and within several weeks have the skills and confidence to design and do high-quality experiments completely on their own. As of Spring 2022, all students in our four largest introductory courses—the algebra- and calculus-based mechanics courses and the electricity & magnetism courses—now get to experience these student-supportive labs.

My research seeks to understand what happens in these classrooms where students hold expertise and agency over their own experiments. How well are students mastering technical skills? How do individual students or their groups respond to experimental and/or social difficulties? How do instructor styles support or inhibit student independence? To answer these questions, I collect and analyze quantitative and qualitative data that includes written work from class, survey responses, and video recordings of student groups working on lab activities. So far, I have learned that the curriculum is effective at developing laboratory skills while increasing students’ resilience in response to challenges. My work both examines and impacts student-student and student-instructor interactions in a reiterative process designed to engage students and instructors in building a better, more supportive learning environment.

*Katie Ansell’s research has been funded by the National Science Foundation under Grant No. DUE 17-12467, by a Strategic Instructional Innovations Program (SIIP) Grant of The Grainger College of Engineering’s Academy for Excellence in Engineering Education (AE3) at UIUC, and by a Faculty Retreat Grant of the Center for Innovation in Teaching & Learning at UIUC. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.*

**DEKRA ALMAALOL**

My research in the Noronha-Hostler group aims to build theoretical simulations of ultra-relativistic heavy-ion collision (URHIC) experiments. My focus is on developing the theory of dissipative hydrodynamics and incorporating all the physical aspects of the collision system in a fully integrated theoretical framework. The goal of my work is understanding the nature of strongly interacting matter, and in particular the formation and properties of the quark gluon plasma (QGP).

In quantum chromodynamics (QCD), the fundamental particles are the quarks and gluons which are confined in bound states forming the strongly interacting hadrons. At high energies, the quarks and gluons become deconfined, and at extremely high energies and/or densities, they even become weakly coupled. The QGP is the deconfined phase of QCD and is transiently formed in URHIC experiments. In the regions where the deconfinement phase transition occurs, the physics of the QCD matter is highly nonlinear and not well understood.

Observations of the momentum distributions of the final-state hadrons (protons, neutrons, and heavier, more exotic, and short-lived assemblages of quarks) produced in URHIC experiments suggest a strong signal of collectivity, and fluid dynamics has been widely and successfully used to describe the dynamics. A challenge that we face in theoretical modeling the experiments is that the QCD matter is produced with large out-of-equilibrium corrections. For this reason, addressing out-of-equilibrium phenomena in hydrodynamics models is essential to building theoretical simulations for these experiments. Part of my research focuses on quantifying the applicability of fluid dynamics in the presence of these out-of-equilibrium corrections, in addition to building in the correct physics describing the QGP dynamics.

An important aspect we focus on in the Noronha-Hostler group is the incorporation of local baryon, strange, and electric charge fluctuations in fluid dynamics. While previously the community was interested in the high temperature and zero chemical potential limit of the QCD phase diagram, understanding charge dynamics is directly relevant to the search for the QCD critical point and the beam energy scan program. Incorporating charge dynamics in the collision system could also introduce qualitative and quantitative impacts on the QGP properties extracted previously, which is something we aim to scrutinize.

*Research in the Noronha-Hostler lab is supported by the U.S. Department of Energy under Grant No. DESC002063, by the National Science Foundation’s support of the MUSES collaboration under Grant No. OAC-2103680, and by an Alfred P. Sloan Foundation Research Fellowship. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the funding agencies.*

**LAIMEI NIE**

Condensed matter theory has long been at the center of interdisciplinary endeavors, with its thriving interactions with quantum information and high energy physics, as well as inseparable connection to experiments. During the past few years my work has focused on the characterization of quantum dynamics in many-body systems. In particular, I’m interested in deterministic quantum evolutions that exhibit chaotic behaviors.

Chaos in the classical world is more or less well understood, but its quantum counterpart remains elusive—even its definition is not completely clear, despite decades of efforts. The glory and mystery of many-body quantum chaos is tightly connected with quantum thermalization, a puzzling phenomenon where certain isolated quantum systems (such as ultracold atomic gases) behave “thermal” under unitary time evolution, without being in contact with a thermal bath.

Furthermore, the footprints of quantum chaos have recently been witnessed in two seemingly disparate research thrusts—resolving the black-hole information paradox and building quantum computers. My research aims to address fundamental questions regarding the precise definition of many-body quantum chaos and its relation to key concepts in condensed matter physics, AMO physics, quantum information, and high- energy physics. By applying insights from quantum entanglement and the anti-de Sitter/conformal field theory correspondence (AdS/CFT), which is sometimes called gauge/gravity duality, my collaborators and I revealed an important, universal aspect of quantum chaotic dynamics: the ability to efficiently and thoroughly delocalize quantum information. We further showed that certain condensed matter toy models and artificial black holes both possess this ability to its maximum extent, making them the perfect candidates for quantum chaotic dynamics.

The other thrust of my research is to understand exotic properties of real-world materials through collaborations with experimental colleagues. For example, in the past I have worked on how disorder affects various charge orders seen in X-ray measurements in high-temperature superconductors. My newly found interest is the search for and characterization of Majorana zero modes in the planar topological Josephson junction, a promising experimental platform for the formulation of topological qubits. With a combination of analytical and numerical treatments of the junction models, we aim to predict the locations of the Majorana modes and perform braiding operations by tuning parameters such as the external magnetic field. Our next step in this work will be to transfer our knowledge of the theoretical models to more realistic setups, to provide guidance and feedback to experimentalists working on these problems.

*Laimei Nie’s research has been funded by the National Science Foundation under Grant Nos. DMR-2004825, OMA-2016136, and DMR-1725401. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.*