Colloquia will be hosted online and will start at 4 p.m unless otherwise noted.
Tom Hartman, Cornell University
Hosted by Ted Jacobson
Wormholes and the Information ParadoxBlack hole evaporation seems to create entropy in a way that violates quantum mechanics. This is the essence of Hawking's black hole information paradox. I will describe recent progress on this problem, including a new result for the entropy of Hawking radiation that is compatible with unitary quantum mechanics, and discuss the consequences for black holes in quantum gravity. The mechanism is a quantum effect in which virtual wormholes modify the leading-order behavior of highly entangled systems. This is part of a wider set of ideas relating geometry to entanglement.
Will Detmold, MIT
Hosted by Zohreh Davoudi
The secret life of quarksQuarks and gluons are the fundamental constituents of most of the visible matter in the Universe but they are never detected directly in experiment. Understanding how protons, neutrons, nuclei and their more exotic cousins emerge from the quantum fluctuations of quarks and gluons is a grand challenge in theoretical physics. At the same time, quarks and gluons hold they key to interpreting some of the most sensitive searches for new physics beyond the paradigm of the Standard Model of particle physics. I will explore how calculations on the worlds largest supercomputers are providing insight into the emergence of the structure of matter and the nature of nuclei at their deepest level and delivering critical inputs into searches for new physics at the LHC and in laboratory based searches for dark matter.
Jim Drake, UMD
Hosted by Bill Dorland
Magnetic Reconnection and Particle Acceleration in Space andMagnetic reconnection is responsible for the explosive release of magnetic energy in space and astrophysical systems. Such impulsive energy release spans a wide variety of environments throughout the universe, including solar and stellar flares, flares in pulsar nebulae, jets in active galactic nuclei and other astrophysical systems. What controls the dynamics of reconnection and the mechanisms responsible for efficient particle acceleration are therefore topics of great scientific interest, especially in light of the goal to interpret simultaneous observations of gravitational waves and electromagnetic signatures in astrophysical events. Observations reveal that a large fraction of released magnetic energy goes into energetic particles, whose distributions take the form of power laws that extend many decades in energy. Theoretical ideas about the mechanism that drives these energetic particles during reconnection have changed dramatically over the past decade. Early ideas that parallel electric fields were the dominant driver have been displaced by a new picture in which the growth and merging of large numbers of magnetic flux ropes both release magnetic energy and efficiently drive energy gain of particles. New computational and analytic models are for the first time reproducing the extended power laws seen in observations. The talk will emphasize basic physical concepts that reveal both the physics of magnetic reconnection and the mechanisms for particle energy gain.
Gianpaolo Carosi, LLNL
Hosted by Anson Hook
Tuning into the Dark Matter AxionThe nature of dark matter is one of the deepest mysteries in physics and cosmology. A preponderance of indirect evidence points to it being compose of new particles beyond the standard model. The Axion, which arises as a byproduct of explaining why the neutron doesn’t have a measurable dipole moment, is one very well-motivated candidate. The Axion Dark Matter Experiment (ADMX) is the DOE High Energy Physics flagship search for axions in the US and is based at the University of Washington in Seattle. ADMX uses a large microwave cavity immersed in a strong static magnetic field to resonantly convert dark matter axions to detectable photons. Recently ADMX has completed its first set of data runs with unprecedented sensitivity in the classical QCD-axion mass range of several µeV and is continuing to take data in a previously unexplored region of parameter space. In this talk I will describe the history of axion dark matter searches, describe the recent ADMX results and near term search prospects and give a survey of the R&D efforts currently underway to explore the entire axion dark matter mass window.
Ed Bertschinger, MITHosted by Sarah Eno
How Departments Change: A Cautionary ExampleAmong the major research universities in the 1970s and 1980s, MIT had an unusually large (though still small) percentage of women and African Americans as both faculty and students in its physics department. This talk discusses how this happened, why it ended, and how this information guided later change efforts. The answers go far beyond one physics department to include biologists, university presidents, and two US presidents.
Chandralekha Singh, University of Pittsburgh
Hosted by Daniel Serrano and Peter Shawhan
How to Enhance Physics by Making It InclusivePhysics faculty members often only focus on content and pedagogical approaches to improve student engagement and learning in physics courses. However, students’ motivational characteristics can also play an important role in their engagement and success in physics. For example, students’ sense of belonging in a physics class, their self-efficacy, and views about whether intelligence in physics is “fixed” or “malleable” can affect engagement and learning. These types of concerns can especially impact the learning outcomes of women and racial/ethnic minority students and stereotype threats can exacerbate these issues. In this colloquium, I will discuss prior research studies that show how different types of social psychological interventions (e.g., social belonging and growth mindset) have improved the motivation and learning outcomes of all students, especially women and underrepresented minorities in STEM fields. These interventions include providing data to students about how intelligence is malleable and one can become an expert in a discipline by working hard in a deliberate manner, sharing with the students examples of testimonials of past students with diverse backgrounds who struggled initially but then succeeded by working hard and using deliberate practice. I will discuss how these ecological interventions were adapted and implemented in our physics classes. These types of interventions are short, requiring less than one hour of regular class time even though they have the potential to impact student outcomes significantly—especially for women and other underrepresented students in physics classes. These findings also have implications for effectively mentoring students who are doing research in physics.
Chandralekha Singh is a professor in the Department of Physics and Astronomy and the Founding Director of the Discipline-based Science Education Research Center (dB-SERC) at the University of Pittsburgh. She is currently the Past President of the American Association of Physics Teachers.
Mimi Heibert, UMD
Hosted by Tim Koeth
The Uranium Club: Tracking Down Lost Radioactive Relics from World War IIAt the end of World War II, a top secret scientific intelligence mission, code named Alsos, was commissioned with the goal of assessing the state of the German nuclear program. What they found when they arrived in the small town of Haigerloch in Germany’s Black Forest, was a deep pit in the floor of an old monastery wine cellar and 664, five centimeter cubes of uranium buried in a nearby field. These were the remains of Werner Heisenberg’s final, failed attempt at building a functioning nuclear reactor.
To the Alsos Mission members, the conformation found at Haigerloch, that the German program had failed at coming anywhere close to creating a sustained nuclear reaction, much less an atomic bomb, was surprising. Germany was not only the birthplace of atomic physics, but the German program had also held a nearly two year head start over the Manhattan Project. Miscalculations, infighting between the scientists and mismanagement from the Nazi government, all combined to ensure the failure of Germany’s nuclear ambitions. The contrasts that can be drawn between the German nuclear program and the Manhattan Project provide lessons in both science and scientific management.
The majority of the uranium cubes found at Haigerloch have largely been lost to history. One, however, made its way to the collection of Dr. Tim Koeth, sparking a years-long research project seeking to investigate how many cubes still remain, where they are now, and what stories they might reveal along the way.
William Ratcliff, NISTHosted by Johnpierre Paglione
Investigations of the First Intrinsic Topological Insulator: MnBi2Te4
In this talk, I discuss our recent results on the first intrinsic antiferromagnetic topological insulator, MnBi2Te4 . In this Van der Waals material, we can control the magnetic state through chemical substitution, as well as through the application of a magnetic field. These knobs allow us to affect the topology of the band structure and thus the transport. We apply a number of probes, including transport, susceptibility, neutron scattering, angle-resolved photoelectron spectroscopy (ARPES), and transmission electron microscopy (TEM) to determine the physics of this exciting material [1,2].
 "Spin Scattering and noncollinear spin-structure induced intrinsic anomalous Hall Effect in antiferromagnetic topological insulator MnBi2Te4," Seng Huat Lee, et al., Phys. Rev. Research 1, 012011 (2019)
 "Ferromagnetism in van der Walls compound MnSb1.8Bi0.2Te4," Yangyang Chen, et al., Phys. Rev. Materials 4, 064411 (2020)
Meeting ID: 987 7803 5497
Dmitry Pushin, Institute for Quantum Computing, University of WaterlooHosted by Charles Clark
Applications of Structured Matter and Light WavesSince their experimental demonstrations a quarter-century ago there has been great progress in the generation, detection, and applications of “structured waves” of light and quantum particles, where the wavefront is patterned to attain nontrivial propagation characteristics such as orbital angular momentum (OAM), nondiffraction, and self-healing. The structured OAM light waves have demonstrated a number of applications in microscopy, encoding and multiplexing of communications, and manipulation of matter. In this talk, I will cover some recent advances in the preparation and application of spin coupled OAM beams, for both neutrons and light. In the case of light, we are exploring a unique application of retinal imaging and detection of age-related macular degeneration. In the case of neutrons, we look at probing emerging quantum materials with interesting topological features.
Sergey Frolov, University of PittsburghHosted by Vlad Manucharyan
How Do We Discover Majorana Particles in Nanowires?Majorana particles are real solutions of the Dirac equation, representing their own antiparticles. In the condensed matter context, Majorana refers to electronic modes in nanostructures described by peculiar ‘pulled-apart’ wavefunctions and by hypothesized non-Abelian exchange. This last property makes them interesting for quantum computing. I will present our efforts to generate and verify Majorana modes in semiconductor nanowires coupled to superconductors. In particular, how can we tell Majorana signatures apart from similar Andreev states that do not have non-Abelian properties? While we may not have a verified Majorana observation now, I will talk about ways to get there: through careful experiments, improved nanowires and device fabrication and with eyes open for alternative explanations.
Meeting ID: 994 8423 2905