Colloquia / Seminars
Tea, coffee, and refreshments are served at the speaker’s reception in Phillips Hall 269, 3:30pm.
Colloquia are held Monday afternoons in Phillips Hall 265, 4:00pm.
The student Questions and Answers will also be held in Phillips Hall 269 after the colloquium, 5:15pm.
Past Fall 2018 Colloquia
The Hubbard Model: From solids to cold atoms and back again
Richard Scalettar, UC Davis
Over the last half-century, the Hubbard Hamiltonian has been extensively studied and applied to some of the most fundamental problems in solid state physics. I will first discuss how it provides simple physical pictures which lead to a qualitative understanding of the origin of magnetism and insulating behavior in transition metal oxides, and even Cooper pairing and density inhomogeneities in high temperature superconductors. Unfortunately, exact solution (either analytic or numeric) of the Hubbard model is not possible except in special limits. In an effort to understand its properties better, attempts have been made over the last decade to emulate the Hubbard model with ultracold atoms. A description of these experiments, and their successes and failures, will be presented. Finally, in just the least year or so, a new proposal has emerged to emulate the Hubbard Hamiltonian using engineered defects in thin silicon sheets. This suggestion returns the model to its solid state roots, and may offer at last a quantitatively accurate revelation of its mysteries.
Physics, Data Science, and Causal Inference
Adam Kelleher, Columbia University, Buzzfeed (recently)
I’ll describe my career path into data science from the Physics PhD program at UNC. I’ll discuss a few projects from throughout my data science career. I’ll try to give a realistic view of what data science is, cutting through some of the hype around machine learning and artificial intelligence. I’ll discuss the value of transferring methods from other sciences into data science, and focus on causal inference as an example.
Sketches from the exotic world of quarks and gluons
Raul Briceño, Old Dominion University
At the core of everyday matter is a complex inner world of subatomic particles. In particular, the nuclei of atoms are made of protons and neutrons, which are themselves made of even smaller particles known as quarks and gluons. Thanks to experiments, like the ones being carried out at Jefferson Lab, we have been able to peer inside and deduce the guiding principles for the behavior of quarks and gluons. This knowledge has been formalized into a fundamental theory of the strong nuclear force, Quantum Chromodynamics (QCD). However, despite having the theory in place for over 40 years, the connection between QCD and experiment has been historically limited by the fact that the strong nuclear force is “strongly interacting”. In this talk, I discuss recent theoretical progress that is finally allowing us to peer into the fascinating world of quarks and gluons.
How to Tell a Great Story about your Research
Jessica Thomas, American Physical Society
I’m a former condensed matter physicist who left research to work in science publishing and communication. Today, I run Physics (physics.aps.org), an online magazine for the American Physical Society that features stories about newsworthy papers in the society’s journals (i.e. the Physical Review.) I’ll give some insight into how we decide which papers to cover and what goes into crafting a good story about them. I’ll also offer some general tips for communicating your research to a broad audience, whether it’s for writing a clear paper and a standout cover letter, or for giving a talk, defending your thesis, or chatting with journalists. Finally, I’ll share my experience as a one-time Ph.D. who chose a career outside of research.
Multiscale Imaging of Cellular Microenvironments
Kevin Eliceiri, University of Wisconsin-Madison
Over the last thirty years the field of Biophotonics, the study of the interaction between light and biological material, has exploded with the advent of advanced labeling and optical imaging technologies that allow for unprecedented imaging resolution with high specificity in cellular and animal models. A major strength of optical imaging is the broad range of scales that are possible, from single molecules to cells. Moreover, the modern tools of fluorescence and bioluminescence imaging are able to bridge cellular studies in a dish to cells and molecules in animal models. However, optical approaches have largely failed to translate to the clinical setting. While this is partially due to the emerging nature of these approaches, the majority of these techniques either do not yet have the depth penetration needed for clinical imaging, or require exogenous labels that are not yet validated in the clinical environment. Despite the clear complementary potential of optical approaches to traditional PET and MRI methods by coupling high resolution and research models with depth penetration and clinical validation, such multimodal approaches are uncommon and not yet used clinically. New techniques that could combine the micron level spatial resolution of optics with the millimeter depth visualization of medical imaging are needed and have great potential. Three collaborative multiscale efforts will be the focus of this talk: 1) Multiscale Imaging instrumentation development 2) Bridge between biomedical and basic researchers and their research models 3) Multiscale Visualization and computational strategies.
Counting distinct states in physical dynamics
Norman Margolus, Massachusetts Institute of Technology
Since counting distinct states is so fundamental in statistical mechanics, why isn’t it a basic quantity in all of physics? It turns out that, in fact, it is. Like entropy, energy is also a maximum count of distinct states—in time. In this talk I review how finite average energy makes distinct-state finite, despite space and time being treated as continuous. I discuss the relationship between maximum distinctness, discreteness and uncertainty. And I show that classical lattice gas models are foundational for dynamics, in the same way that they are in statistical mechanics.
Innovations and applications of high-power optical pumping
F. William Hersman, University of New Hampshire
Optical pumping involves the resonant illumination of a vapor to selectively produce and control a non-thermal distribution of the atomic states. New technologies to select the output wavelength from high-power diode lasers and narrow their spectrum have enabled new and improved applications. We discuss evolution of technology to select the output wavelength and narrow the spectrum from high-power diode lasers that has enabled increased polarization and production rate of hyperpolarized xenon-129. We present a new laser architecture specifically engineered for optical pumping that utilizes an atomic line filter in an external cavity, and speculate on its utility for improving polarized noble gas production as well as underpinning a new high-energy laser technology for ballistic missile defense.
New Views of the Universe
Dragan Huterer, University of Michigan
I will discuss how progress in cosmology over the past decade has improved our understanding of dark matter, dark energy, and the physics of the early universe. I will particularly concentrate on the developments in mapping out the expansion rate of the universe and the growth of density fluctuations in order to better understand dark energy and, eventually, identify the physics responsible for universe’s accelerated expansion. The talk will provide basic background and discuss exciting new developments at a level accessible to graduate students.
Exploring the Primordial Universe with the Cosmic Microwave Background and Beyond
Martin Bucher, Université Paris 7
Cosmology endeavors to characterize, and furthermore to explain, the origin of the universe from the putative big-bang, its evolution to the present epoch, and its structure on very large scales. Early on, cosmology was primarily speculative and theoretical, but with the present observations of the Cosmic Microwave Background (CMB), a highly constrained characterization of the initial conditions of our universe has emerged. I will explain how observations of the CMB from the European Space Agency’s Planck mission seem to favor simple models of Cosmic Inflation. I will also survey efforts to discover the primordial B mode of the CMB polarization, which could be the tell-tale sign of primordial gravitational waves generated during Cosmic Inflation. As the initial conditions of the Universe are now more or less known, emphasis is shifting toward understanding Cosmic Dawn, when the first stars and quasars came into being, and the nature of the Dark Energy, which unexpectedly is causing the expansion of the Universe to accelerate. I will describe efforts to constrain the Dark Energy using observations of the 21 cm hyperfine transition of hydrogen with the forthcoming 1024-dish HIRAX radio telescope in the Karoo Desert in South Africa.
Structural and Functional Imaging of Tissues with Optical Coherence Tomography/Elastography
Kirill Larin, University of Houston
Development of novel methods for structural and functional imaging, monitoring and quantification of different biological processes in tissues and small organs has gained tremendous interest in view of the varied applications of Biomedical Optics. In this talk I will overview several research projects in the Biomedical Optics Lab on development and applications of Optical Coherence Tomography technique for structural and functional imaging of different tissues, such as imaging of mammalian embryonic development and quantifying biomechanical properties of different tissues.
They Call it Free Energy, so, Hey, Why Pay?
James De Yoreo, Pacific Northwest National Laboratory
Nucleation is the seminal process in the formation of ordered structures ranging from simple inorganic crystals to macromolecular films. Recent observations have revealed a rich set of hierarchical pathways involving higher-order species ranging from multi-ion clusters to dense liquid droplets to transient amorphous or crystalline phases. Despite their complexity, a holistic framework for understanding such pathways based on classical concepts emerges when the effects of complexities in free energy landscapes and kinetic factors are considered. I illustrate that framework using in situ TEM and AFM studies of inorganic, organic, and macromolecular systems. The results show that introduction of size-dependent phase stability or high driving force coupled with the existence of metastable polymorphs leads to true two-step pathways characterized by the initial appearance of a bulk precursor. Creation of microstates representing local free energy minima stabi-lized by configurational factors also drives hierarchical pathways, but the intermediates can only exist as transient microscopic entities. Small changes in molecular structure can eliminate these transients and lead to direct nucleation pathways. In either case, reduction in molecular mobility can freeze in non-equilibrium states for kinetic reasons. The findings provide a common basis for understanding the development of order in diverse systems.
Upcoming Fall 2018 Colloquia
Dark Matter, Quantum Computers, and all that.
Reyco Henning, University of North Carolina at Chapel Hill
The international effort to directly detect and determine the nature of cosmic dark matter is experiencing a transition. Weakly Interacting Massive Particles (WIMPs), the traditionally preferred candidates, have come under pressure recently. The Large Hadron Collider has failed to discover a new physical mechanism that would produce WIMPs, and direct detection experiments have come up empty. In this talk I will discuss the axion, which is the leading contender to the WIMP model. A fascinating aspect of searches for axions, which I will also discuss, is the overlap in experimental techniques with radiation detection, quantum computing, NMR, and optics. I will conclude by presenting recent results from two experiments with UNC connections, the MAJORANA DEMONSTRATOR and ABRACADABRA, in the search for axion dark matter.
Kevork Abazahian, University of California, Irvine
Cosmology has entered a precision era, allowing to make inferences of the constituency of the Universe to the sub-percent level on quantities like the density of matter. The density of light, relativistic components like neutrinos can also be inferred, so that limits on the mass of the neutrinos are an order of magnitude stronger from cosmology than the laboratory, albeit with some important caveats. The neutrino sector could hold some surprises, including dark/sterile species that may constitute the dark matter. An unexplained line in X-ray astronomy may indicate a signal of this sort of dark matter, which has initiated several follow-up astronomical and laboratory searches.