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In Spring 2020, snacks & refreshments 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 recent time change.

The student Questions and Answers will also be held in Phillips Hall 269 after the colloquium, 4:45pm.

Fall 2019

Aug 26

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.

Sep 9

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.

Sep 16

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.

Sep 30

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.

Oct 14

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).

Wed Oct 16 @1PM in GA 309

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.

event link: https://physics.unc.edu/event/physics-and-astronomy-colloquium-david-albert/

Oct 21

Iterative Thinking

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.

Oct 28

PT Symmetry

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.

Nov 4

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.

Nov 11

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.

Nov 18

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.

Dec 2

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.

Spring 2020

Jan 27

How the Physics of Nanoparticle Motion in Biological Tissue Can Tell Us Useful Things: A Tale of Ultrasound and Optical Contrast Methods

Amy Oldenburg, University of North Carolina at Chapel Hill

There are many parallels between ultrasonic imaging (US) and optical coherence tomography (OCT). They both produce images of biological tissue by detection of back-reflected waves, and they both are widely employed biomedical imaging modalities. However, US and OCT images often lack specific contrast to tissue properties of interest. In this talk I will describe two emerging US and OCT contrast methods: (1) magnetomotive imaging, in which magnetic nanoparticles are employed to label tissues of interest, and subsequently detected by their motion driven by electromagnets coupled with the imaging hardware, and (2) diffusion-sensitive imaging, in which gold nanorods act as sentinels of their biopolymeric environment by merit of their weakly-constrained Brownian motion. These methods are enabling new applications in a number of Useful Things, such as detecting blood clots, studying tumor growth, monitoring mucus hydration, and imaging tissue viscoelastic properties.

Feb 10

The science of FRIB: From the nuclear many-body challenge to applications of rare isotopes

Alexandra Gade, Michigan State University

There are approximately 300 stable and 3,000 known unstable (rare) isotopes. Estimates are that over 7,000 different isotopes are bound by the nuclear force. It is now recognized that the properties of many yet undiscovered rare isotopes hold the key to understanding how to develop a comprehensive and predictive model of atomic nuclei, to accurately model a variety of astrophysical environments, and to understand the origin and history of elements in the Universe. Some of these isotopes also offer the possibility to study nature’s underlying fundamental symmetries and to explore new societal applications of rare isotopes.

This presentation will give a glimpse of the enormous opportunities that arise once the Facility for Rare Isotope Beams (FRIB) comes online at Michigan State University.

Feb 17

Mechanistic Reasoning about Liquids

Dawn Meredith, University of New Hampshire

Mechanistic reasoning is one of the hallmarks of scientific thinking, but there are gaps in our students’ abilities (and even our abilities!) to reason mechanistically about liquids (both static and dynamic). However, there are conceptual resources for students to build on to allow them to think productively about static and dynamics liquids. These resources are especially important for life science students in our introductory physics course to think about how physical properties of water constrain and enable life.

Feb 24

Turning Photons into Polarized Nuclei

Thad Walker, University of Wisconsin–Madison

Spin-exchange optical pumping (SEOP) uses collisions between optically active and optically inactive species to convert the angular momentum of light into spin angular momentum. I will present a particularly important form of SEOP in which large quantities of noble gas spins, usually He or Xe, can be spin-polarized to nearly 100%. SEOP of noble gases originated with nuclear magnetic resonance gyros in the 1970s, then with the advent of high power tunable lasers became useful for targets for nuclear and particle physics in the 1990s, followed shortly by use in novel forms of magnetic resonance imaging. I with conclude with a few recent examples of precision measurements that use SEOP.

Mar 2

Blast from the Past: Impact of Ultraviolet Emission and Flaring on Exoplanetary Systems and their Habitability

Evgenya Shkolnik, Arizona State University

Roughly seventy-five billion low-mass stars (a.k.a. M dwarfs) in our galaxy host at least one small planet in the habitable zone (HZ). The stellar ultraviolet (UV) radiation from M dwarfs is strong and highly variable, and impacts planetary atmospheric loss, composition and habitability. These effects are amplified by the extreme proximity of their HZs. We now know that these planets are exposed to superflares daily in their first ~100 Myr. Knowing the UV environments of M dwarf planets of all sizes is crucial to understand their atmospheric composition and evolution, providing the needed context for measured exoplanet spectra; while for HZ terrestrial planets, characterization of the UV provides a key parameter in a planet’s potential to be habitable as well as discriminating between biological and abiotic sources for observed biosignatures. Our efforts to study the UV photometrically and spectroscopically of such planetary systems employ past, present and future space telescopes: the Galaxy Evolution Explorer (GALEX), the Hubble Space Telescope (HST), and the upcoming NASA-funded Star-Planet Activity Research CubeSat (SPARCS), due for launch at the beginning of 2022. SPARCS will be a 6U CubeSat completely devoted to continuous photometric monitoring of M stars, measuring their variability, flare rates and evolution, while also being a pathfinder for much-needed future UV missions.

Mar 9 – relocated to Chapman 125

Shape coexistence and triaxiality in atomic nuclei

Akaa Daniel Ayangeakaa, United States Naval Academy

The study of shapes and shape-related phenomena in atomic nuclei have been major themes of research in nuclear physics for more than half a century. In this talk, I will present results of measurements aimed at studying shape coexistence, a rare phenomenon where states located at similar excitation energies, but associated with different intrinsic deformations, coexist and interact. The talk will focus primarily on the electromagnetic properties of low-lying states in 72,76Ge investigated via multi-step Coulomb excitation. The experiments exploit state-of-the-art instruments: the advanced gamma-ray tracking array, GRETINA, and the charged-particle detector, CHICO2. The influence of the axial asymmetry parameter on the shape of these nuclei will be highlighted and the observations confronted with results of calculations within contemporary nuclear models. In addition, new experimental evidence characterizing the precise nature of triaxial deformation in 76Ge will be presented, in connection with the determination of nuclear decay matrix elements involved in neutrinoless double-beta decay (0). The themes and techniques presented in this talk will be an important component of the scientific program at FRIB, the Facility for Rare Isotope Beams that will start operations within the next 1 – 2 years.

Mar 16 – being rescheduled

TarHeel Bus Tour: A Retrospective Discussion

Chris Clemens, Rich Superfine, Dan Young, Suzanne Lye, and Gretchen Bellamy, University of North Carolina at Chapel Hill

The Diversity Committee is thrilled to sponsor our department’s March 16th colloquium, just after spring break. Esteemed colleagues Chris Clemens, Rich Superfine, Dan Young, Suzanne Lye and Gretchen Bellamy will speak about their experiences on the TarHeel Bus tour across the state this past fall. They will share important information about our state, our students, and the issues important to North Carolinians. In lieu of meeting with the colloquium speakers during the day, the Diversity Committee will host a post-colloquium discussion for everyone from 4:30-5 PM (replacing the standard student Q&A) in the same room as colloquium. Please plan to join us for an interesting and thought-provoking discussion!

Mar 23 – rescheduled for Fall 2020

Title TBA

Mini Das, University of Houston

Abstract TBA

Mar 30 – rescheduled for Fall 2020

Illuminating the Nature of Dark Matter via Spin-dependent Interactions

Derek Kimball, California State University, East Bay

Over 80% of the mass in the universe is made up of an invisible substance known as dark matter. Evidence of dark matter’s existence has been found by a wide variety of astrophysical observations. But exactly is dark matter? This is a complete mystery. There are a number of hypotheses that are being tested by experiments throughout the world, among them the idea that dark matter is an ultralight bosonic field that interacts with atomic spins. Cal State East Bay is part of two different international collaborations to test versions of the ultralight bosonic dark matter hypothesis. The Global Network of Optical Magnetometers to search for Exotic physics (GNOME) is a worldwide array of atomic magnetometers that searches for transient signals generated if the Earth passes through an invisible bosonic “wall” or “star” or even from a burst from a cataclysmic astrophysical event such as a binary black hole merger. In the Cosmic Axion Spin Precession Experiment (CASPEr), nuclear magnetic resonance (NMR) techniques are being used to search for oscillating dipole interactions induced by bosonic dark matter fields. We discuss recent and anticipated results of both experiments.

Apr 6 – rescheduled for Fall 2020

Title TBA

Jackie Faherty, American Museum of Natural History

Abstract TBA

Apr 20 – remote option TBD

Title TBA

Dam Son, University of Chicago

Abstract TBA