- The university will hold a virtual town hall for students and their families to answer questions about remote education, student support, and how the UO is protecting campus and the community during the COVID-19 outbreak. The event will be livestreamed from 2:30 – 4:00 p.m. on Monday, March 30 and can be viewed on this webpage. You may submit a question ahead of time anonymously using this web form.
The Physics Colloquium series will resume in Spring term.
Today’s Physics Colloquium will continue as scheduled. (Updated 3/12/20 8:45am)
Date: Thursday, March 12, 2020
Speaker: Ben Farr, UO Physics
Title: The Latest Results from the LIGO-Virgo O3 Observing Run
Abstract: Having recently celebrated the fourth anniversary of the first detection of gravitational waves from a binary black hole merger, the LIGO and Virgo detectors have collected an impressive census of compact binary mergers in the local universe. By the end of the second observing run in August 2017 the LIGO Scientific Collaboration and Virgo Collaboration claimed a total of 10 binary black hole mergers and one binary neutron star merger. The third observing run began in April 2019, and during the first six months the collaborations alerted the astronomical community of 33 merger candidates. The preliminary classifications of these events include 21 binary black hole merger candidates, 4 neutron star black hole merger candidates, and 4 binary neutron star candidates. I will present some of what ground-based gravitational wave astronomy has taught us about compact binaries over the last four years, and what may lie ahead.
Host: Ray Frey
Date: Thursday, March 5, 2020
Speaker: Markus Luty, UC Davis
Title: Classical Radiation Reaction
Abstract: Every physics undergraduate knows that when electrically charged particles accelerate, they radiate away energy and momentum. This means that they must experience a “radiation reaction” force in addition to the Lorentz force. Over 100 years ago, Lorentz and Abraham showed that this force is proportional to the derivative of the acceleration. However, this makes a number of paradoxical predictions, such as runaway solutions and the absence of radiation from charges undergoing constant acceleration. This has led to over a century of conflicting claims in the literature and in textbooks. This talk will give an account of radiation reaction at the advanced undergraduate level that aims to be both understandable and correct. I will give an elementary derivation of the Abraham-Lorentz force using energy and momentum conservation. I then show that in a theory of classical electrons with radius smaller than the classical electron radius, the total energy is unbounded from below, and the theory is catastrophically unstable. If instead the classical approximation breaks down at a radius larger than the classical radius, the structure of the electron cuts off the instability. Although the electron is an elementary particle with no structure, quantum effects cause the classical theory to break down, saving us from this instability. I will close with some comments on radiation reaction for constant acceleration
Host: Spencer Chang
Date: Thursday, February 27, 2020
Speaker: Ben McMorran, UO Physics
Title: Seeing the invisible using electrons
Abstract: New developments in electron optics enable quantum-inspired measurements with electrons. For example, nanoscale diffraction holograms can produce free electron wavefunctions with non-trivial phase profiles that provide a new way to probe the chirality and spatial coherence of nanoscale plasmonics. We report results demonstrating symmetry-breaking inelastic interactions between electron vortex beams and chiral nanoparticle clusters. Nanoscale material phase gratings can also serve as optimized beamsplitters for electrons. We used this in an electron Mach-Zehnder interferometer with large path separation – up to 200 microns – and have demonstrated its use to measure and image electric and magnetic fields at the nanoscale. Recent results on using electron interferometry to probe 3d structure of magnetic skyrmions will be discussed. More recently, we demonstrated interaction-free measurements with this matter wave interferometer. These early demonstrations may also serve as key steps towards novel forms of electron microscopy and spectroscopy that could potentially be used to coherently probe quantum systems – perhaps even manipulate them – as well as image sensitive phase objects like biological molecules with atomic resolution.
Host: Brian Smith
Date: Thursday, February 20, 2020
Speaker: Ethan Minot, Oregon State University
Title: Electrons Dancing on a String
Abstract: Electrons confined to one-dimensional (1d) materials offer fascinating opportunities for applications and fundamental studies. Our group uses individually-contacted carbon nanotubes (CNTs) as a model experimental system to investigate these electrons dancing on strings. I will discuss application areas including sensors, quantum light sources, transistors, and photovoltaics. The unique features of CNTs enable sensors that detect single electrons, light-emitting diodes that emit single photons on demand, band gaps that are driven by tunable Coulomb interactions, and photovoltaic devices with extraordinary quantum efficiency. Beyond our application-driven research, we also explore the fundamental realm. I will discuss measurements of quantum interference effects, and the compressibility of “electron crystals” (Wigner crystals) that form at low temperature and low electron density.
Host: Benjamín J. Alemán
Date: Thursday, February 13, 2020
Speaker: Jason Hogan, Stanford University
Title: Atom interferometry for fundamental physics and gravitational wave detection
Abstract: In recent years, atom interferometry and atomic clocks have made impressive gains in sensitivity and time precision. The best atomic clocks have stability corresponding to a loss of less than one second in the lifetime of the universe. Matter wave interferometers have achieved record-breaking coherence times (seconds) and atomic wavepacket separations (over half a meter), resulting in a significant enhancement in accelerometer and gravity gradiometer sensitivity. Leveraging these advances, atomic sensors are now poised to become a powerful tool for discovery in fundamental physics. I will describe a new type of atom interferometry based on narrow-line optical transitions that combines inertial sensitivity with features from the best atomic clocks, allowing for increased immunity to technical noise and systematic errors. This technique is central to the Mid-band Atomic Gravitational wave Interferometric Sensor (MAGIS) proposal, which is targeted to detect gravitational waves in a frequency band complementary to existing detectors (0.03 Hz – 10 Hz), the optimal frequency range to support multi-messenger astronomy. I will also discuss MAGIS-100, a 100-meter tall atomic sensor now being constructed at Fermilab that will serve as a prototype of such a gravitational wave detector, and that will be sensitive to proposed ultra-light dark matter (scalar and vector couplings) at unprecedented levels.
Host: David Wineland
Date: Thursday, February 6, 2020
Speaker: Brian Nord, University of Chicago
Title: AI In the Sky: The Promise and Peril for the use of Artificial Intelligence in Cosmology and Society
Abstract: Artificial Intelligence (AI) refers to a set of techniques that rely primarily on the data itself for constructing highly accurate models of observed phenomena. AI has had a long history of development, and there has been a recent resurgence in its research and deployment. This is marked by extraordinary results in many contexts across society — from the promise of self-driving vehicles and accelerated biomedical engineering to the peril of automation in the criminal justice system, retail stores, and the military. Moreover, in the last few years, AI has had substantial impacts in the physical sciences, like molecular chemistry, particle physics, and more recently, astronomy.
However, the story is far from over: these techniques face significant challenges to reach their full potential, especially in scientific contexts. During this talk, we’ll first look at modern AI techniques, like neural networks, including the major changes that enabled their rise to prominence. Then, we’ll discuss how the need for significant algorithmic development for trustworthy use in both science and society. This will include examples from astronomy and cosmology, and a vision for where these efforts may take us in the future. Finally, we’ll talk about the implications for AI’s increasing pervasiveness in society and consider our roles as individuals in an increasingly data-driven world.
Host: Tien-Tien Yu
Date: Thursday, January 30, 2020
Speaker: Swapan Chattopadhyay, Fermilab and Northern Illinois University
Title: Particle Accelerator and Emerging Quantum Initiatives at Fermilab
Abstract: Fermilab is building a state-of-the-art high current proton accelerator complex PIP-II in support of DUNE (Deep Underground Neutrino Experiment), its international flagship particle physics experiment, while advancing fundamental accelerator R&D of nonlinear dynamics, high current proton beams, and single electron quantum dynamics in its experimental test accelerator complex FAST/IOTA.
Synergistically, as part of a national DOE ‘Quantum Initiative’, Fermilab is hosting half a dozen funded R&D activities in the science and technology of Quantum Sensors via its emerging strong Quantum Science and Technology Program, including superconducting cavity-based dark matter ‘Axion’ search and prototype 50-qubit quantum computer, quantum algorithms for high energy experimental physics and a 100-meter long-baseline atomic beam interferometer to demonstrate macroscopic atomic quantum entanglement and as a quantum sensor for the dark sector and stochastic cosmic gravitational wave background from the early universe.
I will give a flavor and description of some of these current activities at Fermilab.
Host: Jim Brau
Date: Thursday, January 23, 2020
Speaker: Mike Raymer, UO Physics Dept.
Title: The National Quantum Initiative, or Mr. Raymer goes to Washington
The National Quantum Initiative Act, which passed with strong bipartisan support in Congress and was signed into law by President Trump in late 2018, authorizes up to $1.275B in federal funding over five years and instructs the NIST, NSF, and DOE to work with academic institutions and private industry to catalyze the growth of quantum information science and technology (QIST). What are the main goals, opportunities, and hoped-for outcomes of QIST? What is the state of the art? How did a professor from the UO happen to initiate and organize the lobbying effort that led to passage of the NQI Act? How did Ivanka Trump assist in the process? The answers to some of these questions (without spoilers) can be found in the article:
“The US National Quantum Initiative – from Act to Action,” Christopher Monroe, Michael G Raymer and Jacob Taylor, Science, 3 May 2019, VOL 364 ISSUE 6439
Host: Dave Wineland