Spring 2021 Colloquia

No Physics Colloquium

Georgia Institute of Technology, School of Physics


Abstract: The SARS-CoV-2 virus is a strain of coronaviruses, named for the characteristic trimeric spike (S) glycoproteins that protrude from the viral membrane surface. The S proteins are type I fusion proteins, which upon recognition of ACE2, their host cell receptor, undergo substantial conformational change leading to membrane fusion and viral entry. Using molecular dynamics simulations, we have investigated several aspects for both the conformational landscape of the pre-fusion S protein as well as the receptor-binding process. Before binding, the receptor-binding domain on the S protein must first open to make the binding site accessible. We have carried out free-energy calculations to determine the minimum-free-energy pathway for this opening on the nation’s largest supercomputer, Summit at Oak Ridge National Laboratory. Our simulations reveal, in particular, the role of S-protein glycans in modulating the opening process as well as the roles of key mutations. Next, machine learning applied to multiple microsecond-scale trajectories has allowed us to identify key residues that differentiate between SARS-CoV and SARS-CoV-2 S-protein binding to the receptor. Free-energy perturbation of selected residues further reveals the energetic contributions of individual mutations. Finally, we have also determined the contributions of ACE2 receptor glycans to binding, illustrating in part why SARS-CoV-2 may bind more easily than SARS-CoV.

Bio: Dr. James C. (JC) Gumbart is an Associate Professor of Physics at the Georgia Institute of Technology in Atlanta, GA. He obtained his BS from Western Illinois University in 2003 and his PhD in Physics from the University of Illinois, Urbana-Champaign in 2009 under the mentorship of Klaus Schulten, focusing on the area of computational biophysics. After two years as a postdoctoral fellow at Argonne National Lab working with Benoit Roux, he started his lab at Georgia Tech in early 2013. His lab carries out molecular dynamics simulations aimed primarily at understanding the composition, construction, and function of the Gram-negative bacterial cell envelope and the proteins embedded within.
No Physics Colloquium
Colorado School of Mines, Department of Physics


Bio: I have lived my entire life in Colorado, love teaching physics, and studying how people learn physics. I have taught a range of courses over 15 years from introductory physics to graduate level science education research seminar.

My research focuses on formative assessment and curriculum design. I developed the widely used CLASS, which measures students’ perceptions of physics and how to learn physics; have done extensive work on problem solving evaluation; developed the interface design guidelines for the PhET Interactive Simulations; and most recently developed the PTaP (Perceptions of Teaching as a Profession) instrument. I have also designed and developed several curricula including the Explore Sound project – K-14 materials for acoustics.

Over the years I have also juggled a few other roles, including co-Director of the PhET Interactive Simulations Project, Director of Research for the Science Education Initiative at CU, Boulder, Research Consultant with the Carl Wieman Science Education Initiative at UBC, Education Coordinator for the Acoustical Society of America , and Director of Science Teacher Education Programs at the University of Northern Colorado. Currently I am working with several national societies to build a campaign aimed at recruiting secondary math and science teachers.

Recorded Video Link

Presidents’ Day Break
No Physics Colloquium
No Physics Colloquium
University of Colorado @ Boulder, JILA


Quantum science with neutral atoms has seen great advances in the past two decades. Many of these advances follow from the development of new techniques for cooling, trapping, and controlling atomic samples. As one example, the technique of optical tweezer trapping of neutral atom arrays has been a powerful tool for quantum simulation and quantum information, because it enables control and detection of individual atoms with switchable interactions. In this talk, I will describe ongoing work at JILA where we have explored a new direction for the optical tweezer platform: metrology. I will report our recent progress towards combining scalability and quantum coherence in a tweezer-based optical atomic clock platform, and our efforts towards using quantum information concepts and many-body dynamics to create entangled states that enhance metrological performance. Much of this technology is based in the use of tweezer-trapping of a new family of atoms, alkaline-earth atoms — I will discuss the broader outlook of this direction and new pursuits on the horizon.
Recorded Video Link
Tweezing a New Kind of Atomic Clock

Bio: Dr. Adam Kaufman is an associate JILA fellow and assistant professor adjoint at CU Boulder. He did his PhD at JILA, studying few-body quantum mechanics of atoms in optical tweezers. Afterwards, as a postdoctoral fellow at Harvard, he investigated the dynamics of entanglement in thermalizing many-body systems and other Bose-Hubbard phenomena. In 2017, he moved back to JILA where he has continued working in the field of quantum science with neutral atoms. He is a winner of the prestigious APS DAMOP thesis prize in 2016, and he pioneered the research on atomic clocks based on optical tweezers.

Texas State University, Department of Physics


Abstract: Much has been learned in the past few decades about how to teach undergraduate STEM courses in a way that generates positive and equitable student outcomes. At the same time, many instructional change efforts that aim to support individual instructors in incorporating equitable, student-centered classroom practices have fallen short of achieving widespread change. Instructional change teams are a promising mechanism for achieving sustained improvements to undergraduate STEM courses and are becoming more prevalent in higher education change efforts that focus on systems rather than individuals. Yet team-based change efforts are also much more complex and can fall apart without appropriate support and guidance. For the past five years, my collaborators and I have been pursuing research that aims to reveal how change leaders can provide that support to teams. We have used grounded theory to create a model that highlights key aspects of how instructional change teams work together to achieve various kinds of success. The model includes five team inputs, five team processes, three emergent states (how teams think and feel about their work), and four team outcomes. In this talk, I will describe how we developed this model using interviews with project leaders and team members from across the U.S., as well as literature about teams in other contexts. I will then provide examples of how lessons from the model can be applied in practice by drawing on my own change efforts at Texas State University. Specifically, I will illustrate how this model informed the design of a 5-year, $2.5 million instructional change effort that I am currently co-leading in our college of science and engineering. I will also discuss how the model has helped me to implement a small-scale curriculum development project within my own department. Finally, I will discuss how the initial research project has evolved into a new grant-funded project, and what we hope to accomplish from a practical and research perspective.

Bio: Dr. Alice Olmstead (she/her) is an Assistant Professor of Physics and the Co-director of the Physics Learning Assistant Program at Texas State University. She is also a co-PI and programmatic co-lead on the $2.5 million, 5-year NSF-IUSE-HSI award “Creating Faculty-Student Communities for Culturally Relevant Institutional Change” at her home institution. Her primary research expertise is on strategies that can help STEM faculty to improve their instruction and lead to long-term change. She has also recently been pursuing research related her own teaching, specifically focusing on how to support students’ reasoning about connections between physics/STEM, ethics, and society. She received her PhD in Astronomy at the University of Maryland in 2016 and held a postdoctoral research appointment at the Center for Research on Instructional Change in Postsecondary Education (CRICPE) at Western Michigan University from 2016-2018. She has been at Texas State since 2018.

No Physics Colloquium
University at Buffalo, Department of Physics


Abstract: Electron spin qubits in Si are promising candidates as building blocks toward future scalable quantum computers. Tremendous progress has been made in the past decade in demonstrating the exceptional coherence properties of spins confined in quantum dots and donors. However, studies of high-fidelity manipulation of spin qubits have encountered numerous problems as well: for donors, the small Bohr radius makes donor electrons hard to locate and control; for quantum dots, especially ones in Si/SiGe heterostructures, small valley splitting makes spin detection based on spin blockade difficult to realize. In this talk I discuss our recent work on spin manipulation and decoherence in Si quantum dots. I will first show that the complex valley-orbit coupling in a Si quantum dot can be significantly impacted by the atomistic scale features of an interface. The different valley mixing angles across a double dot would remove all valley selection rules in electron tunneling, and cause significant modification to the two-electron exchange coupling. On the decoherence front, I will discuss our recent study of spin relaxation in a Si quantum dot under the influence of a micromagnet that allows electrical control of single spins in Si. We show that the field gradient generated by a micromagnet amounts to an artificial spin-orbit interaction. However, unlike intrinsic spin-orbit coupling, which causes only spin relaxation, a micromagnet would cause both spin relaxation and pure dephasing, and generate a longitudinal effective field that could potentially be used for spin manipulation.
We thank support by US ARO.

Short Bio: Xuedong Hu is a physics professor at the University at Buffalo, the State University of New York. He received his PhD degree in condensed matter theory from University of Michigan in 1996, supervised by Franco Nori. He was introduced to the field of solid state quantum information processing in 1998 as a postdoc in Sankar Das Sarma’s group at the University of Maryland. His recent research focus is on spin qubits in silicon.

Spring Break
No Physics Colloquium
American Physical Society


Abstract: My path through physics is non-traditional in many ways, and it serves as an example of how the physics discipline can fail Black students even when we are seen as high achieving. In this talk, I will discuss my physics journey, and how I found myself in a career that is focused on pushing the field of physics to become a more equitable space for Black folks. Because my experiences resonate with research findings from studies I have conducted, I will use excerpts from my study participants to demonstrate some common themes of experience for Black physicists. I will wrap up the talk with some ideas about how other members of the physics community can learn to become an agent of change, and what ongoing initiatives are looking to make the field more equitable and just.

Bio: Dr. Simone Hyater-Adams is a physicist, artist, educator, and researcher with a passion for creating more opportunities for Black STEM students. After receiving her B.S. in Physics from Hampton University, she pursued graduate studies at the ATLAS Institute at the University of Colorado Boulder (CU Boulder) where she was a National Science Foundation Graduate Research Fellow. In her graduate research, she used her personal experiences from pursuing physics to guide her interdisciplinary research examining the connections between performance art and identity for Black Physicists. This work was awarded the Harry Lustig Award from the American Physical Society’s Four Corners Section. Currently, Simone manages the American Physical Society’s National Mentoring Community. Concurrently she continues to develop her Performing Physics program, an outreach program that incorporates physics with performance art. In addition to this work, Simone also develops and facilitates equity workshops with goals to cultivate more inclusive and equitable STEM learning and working environments.

University of Wisconsin, Madison, Department of Physics


Quantum computing is based on the manipulation of two-level quantum systems, or qubits. In most approaches to quantum computing, qubits are as much as possible isolated from their environment in order to minimize the loss of qubit phase coherence. The use of nuclear spins as qubits is a well-known realization of this approach. In a radically different approach, quantum computing is also possible for strongly coupled multi-electron spin 1/2 systems, as realized in silicon-based devices. In this talk I will present both a historical overview of how quantum manipulation in silicon has developed, as well as the latest results from both our group at Wisconsin and from around the world. I will discuss our recent demonstration of coherent manipulation of eight different microwave-frequency resonances in a single silicon quantum dot, which starts to glimpse the future prospect of spin qubits being controlled using the types of powerful tools developed for controlling atoms by the AMO community over many decades. I will end with a brief discussion of how silicon fits into the broad quantum science and technology ecosystem, which is growing at an astounding rate. This article in Physics Today discusses closely related material: Quantum computing with semiconductor spins.

Bio: Mark A. Eriksson is the John Bardeen Professor of Physics at the University of Wisconsin-Madison. He received a B.S. with honors in physics and mathematics in 1992 from the University of Wisconsin-Madison and an A.M. (1994) and Ph.D. (1997) in physics from Harvard University. His Ph.D. thesis demonstrated the first cryogenic scanned-gate measurements of a semiconductor nanostructure. He was a postdoctoral member of technical staff at Bell Laboratories from 1997-1999, where he studied ultra-low-density electron systems. Eriksson joined the faculty of the Department of Physics at UW-Madison in 1999. His research has focused on quantum computing, semiconductor quantum dots, and nanoscience. With collaborators he demonstrated the first quantum dot in silicon/silicon-germanium occupied by an individual electron and performed the first experiments to demonstrate the quantum dot hybrid qubit. Eriksson currently leads a multi-university team focused on the development of spin qubits in gate-defined silicon quantum dots. A goal of this work is to enable quantum computers, which manipulate information coherently, to be built using many of the materials and fabrication methods that are the foundation of modern, classical integrated circuits. Eriksson was elected fellow of the American Physical Society in 2012 and of the American Association for the Advancement of Science in 2015.

Colorado State University, Department of Physics


Abstract: Because of hydrogen’s simplicity, its energy levels are well-described by quantum electrodynamics (QED). This had made precision spectroscopy of hydrogen a favorite testbed for bound-stated QED. In addition, assuming the QED calculations are correct, one can use hydrogen spectroscopy to determine the Rydberg constant and the proton-charge radius. Any discrepancy of these constants determined in different systems can indicate new physics. In 2010, such a discrepancy was found [Pohl, R. et al. Nature 466, 213 (2010)] when the proton charge radius in muonic hydrogen was found to be about 5-sigma away from the value found through normal hydrogen spectroscopy (termed the proton-radius puzzle). In this talk, I will discuss our ongoing experiments at Colorado State University to produce additional spectroscopic hydrogen data to address this puzzle. Specifically, we have been measuring the 2S-8D transition in a cryogenic beam of hydrogen, which we hope will provide a new determination of the proton charge radius soon. In addition, I will discuss our efforts at laser slowing our atomic hydrogen beam, which could allow for more precise spectroscopy in the future.

Bio: Dylan Yost grew up in Colorado and obtained his BS in Engineering Physics from the Colorado School of Mines in 2005. While at Mines, he performed undergraduate research with Prof. Durfee and Prof. Ohno. He received his PhD on work with vacuum-ultraviolet frequency combs from the University of Colorado in 2011. In 2012, he was a Humboldt Fellow at the Max Planck Institute for Quantum Optics and worked on precision hydrogen spectroscopy. He is currently an associate professor at Colorado State University. He has received an NSF CAREER award and the NIST Precision Measurement Grant for his hydrogen spectroscopy experiments.

Colorado State University, Electrical & Computer Engineering


Abstract: Heme proteins contain an iron-porphyrin group, which plays a central role in oxygen transport, electron transfer, and catalysis in a wide range of organisms. Their unique redox- and oxygen-sensitive optical absorption spectra form the basis for technologies like pulse-oximetry devices and provided critical clues that led to the discovery of the mitochondrial electron transport chain. This talk will focus on transient (picosecond and femtosecond timescale) optically-excited states of heme proteins, their spectral signatures, and use for nonlinear optical imaging of blood oxygenation, mitochondria, and potential for detection of mitochondrial disease. We will also discuss modeling heme transient absorption responses with a time-correlator approach and active suppression of laser intensity noise with adaptive digital signal processing.

Bio: Jesse Wilson is a Boettcher Young Investigator, Rhoden Professor, and Assistant Professor of Electrical & Computer Engineering at Colorado State University. Prior to joining CSU’s faculty, Jesse trained as a postdoc in Warren Warren’s lab at Duke University, working on in-vivo transient absorption microscopy of melanoma. He earned his PhD in Randy Bartels’ lab at Colorado State University, developing techniques in ultrafast pulse shaping and impulsive Raman spectroscopy.

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