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
Date: Thursday, January 16th, 2020
Speaker: Nick Hutzler, Caltech
Title: Searching for new particles and forces using polyatomic molecules
Abstract: The fact that the universe is made entirely out of matter, and contains no free anti-matter, has no physical explanation. While we cannot currently say what process created the matter in the universe, we know that it must violate a number of fundamental symmetries, including those that forbid the existence of certain electromagnetic moments of fundamental particles. We can search for signatures of these electromagnetic moments via precision measurements in polar molecules, whose extremely large internal electromagnetic fields can significantly amplify these moments. These effects would arise from physics beyond the Standard Model, which enables tabletop searches for new, symmetry-violating particles and forces. With
modern, quantum science techniques to control polar molecules, these searches can currently reach into the TeV scale, and offer many routes to even higher scales. In this talk, I will discuss our lab’s approach to performing these tabletop measurements with polyatomic molecules, whose complex structure offers a unique opportunity to
combine robust precision measurement techniques with laser cooling and trapping. This allows us to build experiments with sensitivity to a variety of new physics sectors, and a route to exploring the PeV scale.
Host: Laura Jeanty
Date: Thursday, January 9th, 2020
Speaker: Nathan Wiebe, UW and Pacific Northwest National Labs
Title: Using machine learning to learn magnetic fields with NV centers at room temperature
Abstract: Nitrogen-vacancy (NV) centers in diamond are appealing nanoscale quantum sensors for temperature, strain, electric fields, and, most notably, magnetic fields. However, the cryogenic temperatures required for low-noise single-shot readout that have enabled the most sensitive NV magnetometry reported to date are impractical for key applications, e.g., biological sensing. Overcoming the noisy readout at room temperature has until now demanded the repeated collection of fluorescent photons, which increases the time cost of the procedure, thus reducing its sensitivity. Here, we show how machine learning can process the noisy readout of a single NV center at room temperature, requiring on average only one photon per algorithm step, to sense magnetic-field strength with a precision comparable to those reported for cryogenic experiments. Analyzing large datasets from NV centers in bulk diamond, we report absolute sensitivities of 60 nT s1/2 including initialization, readout, and computational overheads. We show that machine learning techniques, such as sequential Monte-Carlo methods, allow dephasing times to be estimated simultaneously to the magnetic field and that time-dependent fields can be dynamically tracked at room temperature. Our results dramatically increase the practicality of early-term single-spin sensors.
Host: Steven van Enk
The Physics Colloquium series will resume on Thursday, January 9th, 2020.
Happy Holidays! Wishing you a beautiful holiday season and a new year of peace and happiness!