Colloquium
Fall 2023 Colloquia will be held in Room 307 of the Science and Engineering Research Facility (unless slated as virtual in the schedule below) on Mondays at 3:30 PM, EST.
August 28 |
Travis Humble |
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September 4 |
LABOR DAY HOLIDAY |
NO Colloquium |
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September 11 |
Miguel Madurga |
Tipping the Nuclear Scale: Beta-Decay Spectroscopy of (Very) Neutron Rich Nuclei |
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September 18 |
Lucas Platter |
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September 25 |
Takeshi Egami |
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October 2 |
Sam McKenzie |
From Scientist to Politician: Connecting Skills in Science and Politics |
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October 9 |
FALL BREAK |
NO Colloquium |
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October 16 |
Kevin Pitts |
Measurement of the Anomalous Magnetic Moment of the Muon to 0.20 ppm |
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October 23 |
Rob Appleby |
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October 30 |
James A. Sauls |
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November 6 |
Gaute Hagen |
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November 13 |
Fan Zhang |
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November 20 |
Zohreh Davoudi |
Simulating Nature's Fundamental Interactions: From Classical Computations to Quantum Simulations |
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November 27 |
Stephen Taylor |
NANOGrav: The Dawn of Galaxy-scale Gravitational Wave Astronomy |
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December 4 |
Josh Pierce |
Discovery and Innovation in Quantum Science and Technology
The Quantum Science Center is a National Quantum Information Science Research Center headquartered at Oak Ridge National Laboratory. The purpose of the center is to discover and innovate in the field of quantum information science (QIS) to ensure American scientific leadership, economic competitiveness, and national security. QSC addresses this mandate by targeting three major scientific challenges 1) quantum simulation platforms for scientific discovery applications, 2) quantum sensing for real-world applications, and 3) topological quantum materials for new quantum devices. This talk will give an overview of the center's scientific goals as well as highlights of recent scientific impacts and their outcomes in each of these areas.
Tipping the Nuclear Scale: Beta-Decay Spectroscopy of (Very) Neutron Rich Nuclei
The continuing development of production and separation techniques allowing for the study of nuclei far away from the line of stability has spurred the low energy nuclear field for the past three decades. Large proton-neutron imbalances drive emerging exotic phenomena such as shape coexistence or halo distributions of nuclear matter, which in turn have helped refine our understanding of the nuclear interaction in the nuclear medium. In this talk I will discuss our experimental efforts using beta-delayed gamma and neutron spectroscopy to characterize the nuclear structure of neutron rich nuclei around doubly magic 132Sn. In particular I will concentrate in the role nucleon excitations across shell closures play in all three regions, driving both increasingly smaller decay-half lives and larger neutron branching ratios.
Effective Field Theories in Nuclear Physics
In the simplest electroweak nuclear reaction, the proton-proton fusion process, two protons combine into a deuteron while emitting a positron and a neutrino. It is the starting point of the chain of fusion reactions that generate the sun's energy. Only effective field theory can provide a high precision, first principles description of this process needed for modern stellar models. Such a calculation requires not only the nuclear interaction but also electroweak one- and two-body currents derived in a consistent effective field theory framework. I will review the effective field formalisms used to describe this process. I will explain how it depends on fundamental electroweak two-nucleon properties, and how these can be measured in complementary experiments. I will also discuss how the same tools as in proton-proton fusion can be used to describe electroweak processes involving so-called halo nuclei consisting of a tightly bound core and weakly bound valence nucleons.
Figuring Out Dynamic Correlation in Disordered Systems: Glass Transition and High-Temperature Superconductivity
Particle interactions create static and dynamic correlations even in seemingly disordered systems, and such correlations determine the properties, for instance through the fluctuation-dissipation theorem. Thus, figuring out such correlations is the key to understanding dynamic aperiodic matter (DAM), such as liquid, glass and itinerant electrons (Fermi liquid). However, correlations are often concealed and hard to detect by experiments, making the studies difficult, but interesting. I discuss two recent breakthrough examples by my research group, one on the glass transition and the other on the high-temperature superconductivity (HTSC). These two appear totally disconnected, but actually similar experimental approaches to dynamic correlation, the dynamic pair-distribution function determined by neutron/x-ray scattering or by simulation, brought us to the goal. In the case of the glass transition the discovery of density wave instability in liquid was the key [1], and for the HTSC the crucial step was the recognition that the electron dynamics affects electron correlation and the Bose-Einstein condensation [2].
1. T. Egami and C. W. Ryu, Frontiers in Materials, 9, 874191 (2022); J. Phys: Condens. Matter, 35, 174002 (2023).
2. T. Egami, Physica C, 613, 1354345 (2023).
From Scientist to Politician: Connecting Skills in Science and Politics
Plato is quoted as saying "If you do not take an interest in the affairs of your government, then you are doomed to live under the rule of fools." Scientists have long been underrepresented in seats of political power. The 117th Congress had only one physicist, one chemist, and one geologist. In my talk I will discuss what it is like transitioning from being a scientist managing maintenance on the Spallation Neutron Source at the Oak Ridge National Laboratory to a career in local and state politics, and how my scientific training has aided my decision making.
Measurement of the Anomalous Magnetic Moment of the Muon to 0.20 ppm
Previous measurements of the anomalous magnetic moment of the muon have shown a sizeable discrepancy with standard model calculations, which might be indicative of new physics. We present a new measurement from the Fermilab Muon g-2 experiment with twice the precision of our prior result.
The Upgrade of the Large Hadron Collider, What the UK is Doing, and How We Are Telling People About It
The Large Hadron Collider at CERN is a two-beam proton synchrotron with a design energy per proton beam of 7 Tera-electron volts. It has been operating at CERN since 2010, with the high-profile success of finding the Higgs boson in 2012, thus completing the standard model of particle physics. The collider has been running since, and now preparations are being made to upgrade the collision rate (luminosity) of the proton collisions through the HL-LHC project. This upgrade will permit high precision measurements and more sensitive particle searches and involves considerable accelerator upgrade. This talk will review the LHC accelerator, the luminosity upgrade and present some of the UK's contributions to this project. Following this, several public engagement projects linked to the LHC are presented, which attempt to communicate the science of the LHC to a range of diverse audiences, using a range of diverse methods.
The Left Hand of the Electron
Sixty plus years ago parity violation by the weak force was demonstrated in experiments led by Chien-Shiung Wu on the asymmetry of electron currents emitted in the beta decay of polarized 60Co. The asymmetry reflects two broken symmetries - mirror reflection and time-reversal, the latter imposed by an external magnetic field. The same year Bardeen, Cooper and Schrieffer published the celebrated BCS theory of superconductivity, and soon thereafter P. W. Anderson and P. Morel proposed that the ground-state of liquid 3He (the light isotope of Helium) was possibly a BCS superfluid exhibiting spontaneously broken mirror reflection and time-reversal symmetries. Indeed superfluid 3He-A, discovered in 1972, is the realization of a quantum state of matter that violates both parity and time-reversal symmetry. Definitive proof of broken mirror symmetry in 3He-A came 41 years later from the observation of asymmetry in the motion of electrons in superfluid 3He-A.1 I discuss these and related discoveries, as well as the physics underlying anomalous electron transport in such quantum systems with broken mirror and time-reversal symmetries.2,3
- H. Ikegami, Y. Tsutsumi, & K. Kono, Chiral Symmetry in Superfluid 3He-A, Science, 341,59–62, 2013.
- O. Shevtsov & J. A. Sauls, Electrons & Weyl Fermions in Superfluid 3He-A, Phys. Rev. B, 94, 064511, 2016.
- V. Ngampruetikorn & J. A. Sauls, Anomalous Thermal Hall Effect in Chiral Superconductors, PRL 124, 157002 (2020). † Research supported by NSF grant DMR-1508730.
Frontiers in ab-initio Computations of Atomic Nuclei
Atomic nuclei exhibit multiple energy scales ranging from hundreds of MeV in binding energies to fractions of an MeV for low-lying collective excitations. Describing these different energy scales within an ab-initio framework is a long-standing challenge. In this talk I will show how we overcome this challenge by using high-performance computing, many-body methods with polynomial scaling, and ideas from effective-field-theory. This progress enables us to address fundamental questions related to the how nucleons organize themselves in shell away from the valley of beta-stability, nuclear deformation and the limits of the nuclear chart, the role of meson-exchange currents and strong correlations in Gamow-Teller transitions, and the nature of the neutrino from computations of neutrino-less double beta decay and lepton-nucleus scattering on relevant nuclei. New ways to make quantified predictions are now possible by the development of accurate emulators of ab-initio calculations. These emulators reduce the computational cost by many orders of magnitude. This allows us to perform global sensitivity analysis, and use novel statistical tools to make quantified predictions for the neutron skin in 208Pb, the binding energy of exotic 28O, and what drives deformation in neon and magnesium isotopes. With this talk I hope to convey that the accurate computation of multiscale nuclear physics demonstrates the predictive power of modern ab initio methods.
Interacting Electrons in Elementary Graphene
A recurring theme in condensed-matter physics has been the discovery and exploration of macroscopic quantum phenomena as consequences of strong electron-electron interactions, such as magnetism, superconductivity, and fractionalization. Bilayer graphene with a magic-angle artificial twist exemplifies a new paradigm of strongly interacting electrons, as witnessed in the past five years. In fact, naturally occurring rhombohedral graphene multi-layers are also fertile ground for strongly interacting electron physics. In this talk, I will first discuss their theory-oriented spontaneous chiral symmetry breaking, topological orbital magnetization, and quantum anomalous Hall effect at charge neutrality, which have all been observed in experiment. Then I will introduce their experiment-oriented ferromagnetism, superconductivity, electron crystallization, and fractional quantum anomalous Hall effect under ultra-low doping. If time permits, I will show how SU(3) flavor physics analogous to the quark model can also emerge in this system.
Simulating Nature's Fundamental Interactions: From Classical Computations to Quantum Simulations
The strong force in nature, which is at the core of nuclear-physics phenomena, is described by the theory of quantum chromodynamics (QCD). It has long generated an active and growing field of research and discovery. In fact, despite the development of QCD more than half a century ago, plenty of questions remain open into the 21st century: What does the phase diagram of matter governed by strong interactions, such as the interior of neutron stars, look like? How does matter evolve and thermalize after energetic processes such as after the Big Bang or in particle colliders? How do elementary particles in QCD and their interactions give rise to the complex structure of a proton or a nucleus, and their response to various probes? A successful program called lattice QCD has enabled a first-principles look into some properties of matter with the aid of classical computing. At the same time, we have yet to come up with a more powerful computational tool to predict the complex dynamics of matter from the underlying interactions. Can a large reliable (digital or analog) quantum simulator eventually enable studies of the strong force? What does a quantum simulator have to offer to simulate QCD, and how far away are we from such a dream? In this talk, I will describe a vision for how we may go on a journey toward quantum simulating QCD, by taking insights from early to late developments of lattice QCD and its achievements, by motivating the need for novel theoretical, algorithmic, and hardware approaches to quantum-simulating this unique problem, and by providing examples of the early steps taken to date in establishing a quantum-computational lattice-QCD program.
NANOGrav: The Dawn of Galaxy-scale Gravitational Wave Astronomy
For more than 15 years, NANOGrav and other pulsar-timing array collaborations have been carefully monitoring networks of pulsars across the Milky Way. The goal was to find a tell-tale correlation signature amid the data from all those pulsars that would signal the presence of an all-sky background of nanohertz-frequency gravitational waves, washing through the Galaxy. At the end of June this year, NANOGrav finally announced its evidence for this gravitational-wave background, along with a series of studies that interpreted this signal as either originating from a population of supermassive black-hole binary systems, or as relics from cosmological processes in the very early Universe. I will describe NANOGrav's journey up to this point, what led to the ultimate breakthrough, how this affects our knowledge of supermassive black holes and the early Universe, and what lies next for gravitational-wave astronomy at nanohertz frequencies.
Dynamic Nuclear Polarization for Neutron Crystallography
Protein crystallography is an established technique for determining the structure and function of many protein systems. These measurements are essential for drug design, enzymology, and more. Light sources dominate this field due to their extremely high brightness, but neutrons have unique advantages such as sensitivity to light nuclei and isotopes. At ORNL, Dynamic Nuclear Polarization (DNP) is being used to take advantage of the nuclear spin dependence of neutron scattering and leverage that to overcome the large brightness disadvantage of neutron sources. The DNP technique will be described, as will test results, and the design and operation of a DNP enhanced IMAGINE instrument which will soon be installed at the High Flux Isotope Reactor (HFIR).