Colloquia / Seminars
In Fall 2020, the UNC Department of Physics and Astronomy and the Duke Physics Department presents general physics lectures by Duke and UNC faculty for members of both departments. Lectures will be delivered via Zoom with links distributed via email.
M Aug 24
Quantifying the Shear Viscosity of Nature’s Most Ideal Liquid
Steffen Bass, Duke University
Collisions of heavy nuclei at ultrarelativistic velocities are currently utilized at the Relativistic Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC) to recreate matter at temperatures and densities as have only existed in the early universe, a couple of microseconds after the Big Bang. This Quark-Gluon Plasma (QGP), consisting of deconfined quarks and gluons, is nearly an ideal fluid with zero viscosity.
A primary goal of heavy-ion physics is the measurement of the fundamental properties of the QGP, notably its transport coefficients and initial state properties. Since these properties are not directly measurable, one relies on a comparison of experimental data to computational models of the time-evolution of the collision to connect measured observables to the properties of the transient QGP state.
Over the last few years the Duke QCD group has developed techniques based on Bayesian statistics that allow for the simultaneous calibration of a large number of model parameters and the precision extraction of QGP properties including their quantified uncertainties. The analysis has provided the first determination of the temperature-dependent viscosity of the QGP.
W Sep 9
The Search for the QCD Critical Point
Gökçe Basar, University of North Carolina at Chapel Hill
The strong force binds the building blocks of protons and neutrons, quarks and gluons, together and creates most of the observed mass in the universe. At a few trillion degrees, these bonds break, and matter transitions into a new phase called Quark Gluon Plasma (QGP). QGP once filled the universe when it was microseconds old, and today is recreated in the heavy ion collision experiments with the goal of understanding how matter behaves at these extreme temperatures and densities. What do we know about the phases of matter at these extreme environments? What is the nature of the phase transition between ordinary matter and QGP? Is there a critical point in the phase diagram and if there is how can we locate it? I will give an overview of the status of the theoretical and experimental efforts to answer these questions as well as the future challenges.
M Sep 21
Experiments with Quantum Materials
Sara Haravifard, Duke University
Just as the discovery of semiconductors revolutionized the electronics industry in the twentieth century, the development of Quantum Materials holds the key to new advances in technology. There is much basic scientific research still necessary to unveil the tantalizing potential of Quantum Materials. To that end, my research program is focused on advancing our ability to design, synthesize and characterize Quantum Materials. This talk will focus on two main topics: (1) our efforts to study the properties of a specific class of Quantum Materials, the so-called “Quantum Spin Liquids” (QSL), in which spins of the constituent electrons are predicted to become strongly entangled and fail to form a static ordered state as in a conventional magnet; and (2) our work to investigate the underlying properties of a recently discovered class of Quantum Materials, the so-called “Topological Magnon Insulators (TMI).” We are designing a recipe for synthesizing perfect TMI candidates and developing probes to reveal their topological nature directly and unambiguously.
W Sep 30
Physics and Energy
Robert Jaffe, Massachusetts Institute of Technology
Energy is a central concept in physics. Because energy is conserved, it is possible to understand the behavior of complex systems by tracing the flow of energy through them. On the other hand, we humans “consume” energy, degrading it into less useful forms, as it powers modern societies. Providing energy for the world to use in a sustainable fashion is a major, perhaps existential challenge for humankind in the 21st century. The scale and scope of the problem is enormous. The implications for Earth and human societies are profound. Economic considerations and political decisions will be central to any attempt to address this energy challenge. However, decisions made in the absence of good scientific understanding have the potential to waste vast amounts of effort and resources and to adversely affect countless lives and large ecosystems. A clear understanding of the science of energy is essential for specialists and non-specialists alike. Physicists and our universities have a responsibility to provide this understanding. In response to this challenge, Washington Taylor and I developed a physics course for MIT undergraduates and an associated textbook – “The Physics of Energy” — that focus on the sources and uses of energy, and on energy systems and the externalities associated with energy use, including climate change.
W Oct 7
Exploring Beyond the Standard Model with Lattice QCD
Amy Nicholson, University of North Carolina at Chapel Hill
While the Standard Model (SM) of particle physics has been enormously successful in describing the world around us, there still remain many important and unanswered questions requiringBeyond the SM (BSM) physics. One way to experimentally probe the limits of the SM is to search for potential violations of its fundamental symmetries by utilizing properties of special atomic nuclei which enhance these rare events. Connecting experimental signals from nuclear environments to a particular BSM model requires the numerical solution of Quantum Chromodynamics (QCD), a cornerstone of the SM which governs the nuclear interactions. In this talk I will discuss the use of Lattice QCD as a tool for numerically calculating matrix elements relevant for experimental BSM searches. I will use neutrinoless double beta decay, which, if observed, could offer an explanation for the matter-antimatter asymmetry of the universe, as a key example.
M Oct 19
Active Biological Matter and Mechanosensing
Christoph Schmidt, Duke University
Thermodynamic non-equilibrium is a defining feature of living systems on all levels of organization. Cells and tissues are built of “active matter”, dynamic materials with built-in force generators. Such materials self-organize in biological systems into well-ordered dynamic steady states, sustained by the dissipation of metabolic energy. We use advanced light microscopy as well as microscopic motion and force-sensing techniques to characterize the complex mechanical properties of and the motion and stress patterns in biological active matter, in particular the actin cortex, both in reconstituted model systems and in cells. I will introduce methods to detect and quantitate thermodynamic non-equilibrium using fundamental concepts of statistical physics such as the fluctuation-dissipation theorem and the principle of detailed balance.
Closely related to mechanical activity in biological systems are mechanosensory processes. I will present some recent results we obtained on mechanosensitive channels in bacteria.
W Nov 4
A night at high speed: exploring the minute-cadence sky with the Evryscopes
Nicholas Law, University of North Carolina at Chapel Hill
The Evryscopes are array telescopes which cover the entire visible sky in each and every exposure. Based in the mountains of Chile and California, the systems together take a 1.3 Gigapixel image of the sky every two minutes, reaching depths of 16th magnitude in each exposure and much deeper with coadding. I will present the Evryscopes’ view of what happens on a typical night across the sky: superflares blasting habitable worlds, gravitational wave event counterparts, mysterious millisecond-timescale flashes appearing everywhere, and a host of other phenomena. I will also for the first time present the Argus Array, the next-generation Evryscope which will observe far further out into the Universe.
W Dec 2
Quantum Information Science Landscape and NIST
Carl J. Williams, Deputy Director, Physical Measurement Laboratory, National Institute of Standards and Technology
In the early 1900’s, Niels Bohr, Albert Einstein and others laid the foundations of quantum mechanics — nature’s instruction book for the smallest particles of matter. Now 100 years later researchers are primed to harvest the fruits of basic research resulting from Quantum Information Science – the confluence of Information Science and Quantum Mechanics – two of the revolutionary developments of the 20th Century. Quantum information scientists have already convincingly demonstrated the long-term feasibility of these new approaches and there are now an emerging number of niche applications, including NIST’s own quantum logic clock as well as revolutionary new approaches to communication and computing.
The colloquium will begin with a brief introduction into how science policy is made in the United States and describe the international landscape that led to the passage of the National Quantum Initiative (NQI) Act in December 2018. I will then describe NIST’s role within the NQI before moving on to focus on several research highlights from the NIST laboratories. I will then conclude with a few remarks on the potential implications of this technology for science, the economy, and public welfare.