Colloquia / Seminars
In Fall 2019, tea & coffee are served at the speaker’s reception in Phillips Hall 269, 3:00pm.
Colloquia are held Monday afternoons in Chapman Hall 201, 3:30pm. Please note the time change.
The student Questions and Answers will also be held in Phillips Hall 269 after the colloquium, 4:45pm.
Past Fall 2019 Colloquia
Biophysical contrast mechanisms for biomedical imaging
Giuliano Scarcelli, University of Maryland
The interaction between photons and acoustic phonons within materials, first described by Leon Brillouin, has been widely investigated to characterize mechanical and physical properties of samples. To translate this technology to biomedical applications where mechanical properties are often critical, our lab has developed high-resolution spectrometers at high throughput and combined them with optical microscopes to yield 3D imaging modalities that use label-free biophysical properties as contrast mechanisms for imaging. Our first area of application has been in ophthalmology as the loss of corneal strength leads to ectasia and is a major risk factor for refractive surgery complications. To address this issue, we have developed an in vivo Brillouin ophthalmoscope and encouraging data show we can differentiate ectatic corneas as well as characterize outcome of emerging treatments. Recently we have demonstrated increased Brillouin microscopy resolution to characterize intracellular modulus and we developed a flow cytometry platform to rapidly characterize cells based on their mechanical properties. Finally, we will discuss the physics behind the interpretation of Brillouin spectral signatures in the context of soft matter such as cells and tissues.
ZFOURGE & MOSEL : Emergent Galaxies at z~3.5
Kim-Vy Tran, Texas A&M University, University of New South Wales
ZFOURGE and MOSEL are deep observational surveys that track how galaxies assemble over cosmic time. ZFOURGE identifies approximately 70,000 objects up to redshifts of z~7 using a custom set of near-infrared imaging filters that provide high precision photometric redshifts. MOSEL targets emergent galaxies from ZFOURGE for spectroscopic follow-up to track this rapidly evolving population. Here I highlight results that include building a library of composite Spectral Energy Distributions (SED), using the SED fitting code Prospector to determine star formation histories for a range of galaxy populations, and comparing galaxy kinematics at z~3 to cosmological simulations.
Weighing in on Neutrinos — First Results from the KATRIN Experiment
John Wilkerson, University of North Carolina at Chapel Hill
Over the past generation, a series of challenging experiments have revealed that neutrinos have unexpected properties and non-zero masses. These revolutionary discoveries revealed shortcomings in the standard model of fundamental interactions and in our understanding of the role neutrinos play in astrophysics and cosmology. Many intriguing questions remain with profound implications. Might neutrinos offer an explanation of the observed matter-antimatter asymmetry in the universe? What are the masses of the neutrinos and what is the underlying mass mechanism? Can hints of sterile neutrinos be substantiated? This talk will review our current understanding of neutrinos and then turn to the question of how does one “weigh” neutrinos? The latest results from cosmology, double beta decay and direct kinematical methods will be presented, including a first result from the Karlsruhe Tritium Neutrino experiment (KATRIN). As part of the story, the neutrino’s intertwined relationship with and impact on nuclear physics, astrophysics, and cosmology will be explored.
Building with Crystals of Light and Quantum Matter: From clocks to computers
Ana Maria Rey, JILA, NIST, & University of Colorado Boulder
Understanding the behavior of interacting electrons in solids or liquids is at the heart of modern quantum science and necessary for technological advances. However, the complexity of their interactions generally prevents us from coming up with an exact mathematical description of their behavior. Precisely engineered ultracold gases are emerging as a powerful tool for unraveling these challenging physical problems. In this talk, I will present recent developments at JILA on using alkaline-earth atoms (AEAs) –currently the basis of the most precise atomic clock in the world– for the investigation of complex many-body phenomena and magnetism. I will discuss ideas to use AEAs dressed by laser fields to engineer analogs of spin-orbit coupled Hamiltonians, as well as new forms of matter with no yet known counterpart in nature. Finally, I will discuss recent ideas on how atomic collisions can realistically be used for entanglement generation in atomic clocks which are already the state-of-the-art. These investigations would open a path for the practical improvement of world-leading quantum sensors using correlated many-body fermionic states as well as new possibilities to use the new generation of atomic clocks for quantum information processing.
Tracing the gaseous surrounds of galaxies
Virginia Kilborn, Swinburne University
Observations of the neutral atomic hydrogen (HI) component of galaxies is a powerful mechanism to probe the physical properties of galaxies in the nearby Universe. HI is generally found in star-forming, disk galaxies whilst early-type galaxies are generally gas-poor. However recent surveys have uncovered disk galaxies with little HI — and conversely early-type galaxies which are gas-rich. I will discuss the physical mechanisms driving gas content in galaxies, including mass, environment and kinematics. We are heading into a new era of next-generation radio telescopes which will revolutionise our understanding of the HI component of galaxies. I’ll explain how these surveys plan to operate, and show some recent results from one particular telescope, the Australian SKA Pathfinder (ASKAP).
How to teach Quantum Mechanics – Part II
David Albert, Columbia University
I distinguish between two conceptually different kinds of physical space: a space of ordinary material bodies, which is the space of points at which I could imaginably place (say) the tip of my finger, or the center of a billiard-ball, and a space of elementary physical determinables, which is the smallest space of points such that stipulating what is happening at each one of those points, at every time, amounts to an exhaustive physical history of the universe. In all classical physical theories, these two spaces happen to coincide – and what we mean by calling a theory “classical”, and all we mean by calling a theory “classical”, is (I will argue) precisely that these two spaces coincide. But once the distinction between these two spaces in on the table, it becomes clear that there is no logical or conceptual reason why they must coincide – and it turns out (and this will be the main theme of my lectures) that a very simple way of pulling them apart from one another gives us quantum mechanics.
Aaron Titus, High Point University
Numerical techniques for integration are hardly taught in a typical calculus course and are hardly used in a typical physics course. Yet, numerical integration is an essential tool in current research and development in science and engineering. How do we bridge this gap between what contemporary students need and what we traditionally teach? The answer is to think iteratively. I will demonstrate how iterative thinking in the introductory calculus-based physics course allows students to construct, test, and extend physical models and observe the emergence of complex behavior from simple physical rules. I will present examples using VPython (or the web-based version, GlowScript) which provides 3D visualization and a low barrier to learning computational modeling.
Carl Bender, Washington University in St Louis
By using complex-variable methods one can extend conventional Hermitian quantum theories into the complex domain. The result is a huge and exciting new class of parity-time-symmetric (PT-symmetric) theories whose remarkable physical properties are currently under intense study by theorists and experimentalists. Many theoretical predictions have been verified in recent beautiful laboratory experiments.
Dark Matter Challenges of the Solid State
Piers Coleman, Rutgers University
At the turn of the 20th century, physicists faced an uncanny range of unsolved problems: simple questions, such as why hot objects change color, why matter is hard and why the sun keeps on shining, went unanswered. These problems heralded a new era of quantum physics. What was truly remarkable about discovery in this heroic era, was the intertwined nature of research in the lab and in the cosmos: solving superconductivity really did help answer why the sun keeps on shining, while looking at the stars provided clues as to why matter is hard.
The challenges facing us today, epitomized by our failure to quantize gravity and the mysteries of dark matter and energy, are not just problems facing particle physics and astronomy, but problems that challenge physics to its core. What is perhaps less well known, is that physics in the lab and cosmos remain just as intertwined as they were a hundred years ago.
I will discuss the less well-known dark matter challenges of the solid state, epitomized by the strange metals with linear resistivity that accompany high temperature superconductivity, the discovery of insulators with Fermi surfaces and the phenomenon of Quantum criticality. I will argue that these laboratory-scale problems challenge our fundamental understanding of emergent quantum matter in ways that are no less intertwined with their cosmological counterparts than they were a hundred years ago.
Where Do Galaxies End?
Michael Shull, University of Colorado
I review recent observations and theoretical estimates of the spatial extent of galaxies. Galaxies are defined as systems of stars and gas embedded in extended halos of dark matter and formed by the infall of smaller systems. Their sizes are determined by gravitational structures, gas dynamics, and chemical enrichment in heavy elements produced by stars and blown into extragalactic space by galactic winds. The full extent of galaxies is poorly determined. The “virial radius” and “gravitational radius” provide estimates of the separation between collapsed structures in dynamical equilibrium and external infalling matter. Other measurements come from X-ray emission and ultraviolet absorption lines from metal-enriched gas in galactic halos. Astronomers have now identified large reservoirs of baryonic matter in the circumgalactic medium (CGM) and intergalactic medium (IGM) that contain 50-70% of the cosmological baryons formed in the Big Bang. The extent of the bound gas and dark matter around galaxies such as our Milky Way is approximately 200 kpc (650,000 light years). Investigations of physical processes at the “edge of galaxies” are crucial for interpreting new observations of the CGM and IGM, and their role in sustaining the star formation in galaxies.
When the Monster Awoke: Dating the Most Recent Major Flare of Our Galaxy’s Supermassive Black Hole
Gerald Cecil, University of North Carolina at Chapel Hill
The historical power output of mass accreted onto the 4 million solar mass black hole at the center of our galaxy 26,000 light years distant have been estimated from ionization/recombination X-ray spectra of its surroundings. These show that ~500 years ago it was ~200,000 times more luminous than today, but faded within the last century to its current feeble state. I will present our team’s evidence from ground- and Hubble-based spectra and photoionization modeling that this region was a billion times more luminous than at present for many hundred-thousand years ~3.5 million years ago. The principle “transceiver” of this powerful outburst is an angular arc of the Magellanic tidal Stream, 200,000 light years distant from us. Patches of this gas stream within the radiation pattern of the central black hole are too bright and too highly ionized to have been photo-energized by just Milky Way starlight. Model consistency points to a prolonged flare from the central black hole, not a sustained starburst. It occurred within the most recent 1/3000th history of our galaxy, so has repeated often to synchronize all Galactic inhabitants who are aware of electromagnetism. Being very nearby, this interaction will provide unique insights into the influences of the central black hole present in most galaxies.
Upcoming Fall 2019 Colloquia
The Holographic Mystique
Dmitri Khveshchenko, University of North Carolina at Chapel Hill
In the recent years, there has been a remarkable proliferation of the holographic techniques originating from ‘bona fide’ string theory into a number of other fields, including condensed matter. This emergent confluence of ideas from high energy, gravity, quantum information, and many-body theory has become a new frontier where some of the most challenging fundamental questions are being addressed. However, many of the current condensed mater-related holographic applications remain deeply controversial and their true status is yet to be ascertained. In this talk I’ll review the state of the field, focusing on a few condensed matter examples of analogue holography (flexible graphene and optical metamaterials) as well as its soluble (Sachdev-Ye-Kitaev and Witten-Gurau) toy models.