Action at the Edge: Interfaces in Superconductors and Outlaw Quantum Systems

In this colloquium, we will embark on a fascinating journey to the frontiers of condensed-matter physics, exploring the intriguing world of superconductors and the territory of ‘outlaw’ quantum systems.

Superconductors, known for their zero electrical resistance, have long been a subject of intense study. Critically, when interfaces are embedded into superconductors, they generate a rich variety of emergent properties, which lay the foundation for intriguing questions of fundamental physics as well as for applications such as the exploration of mineral resources or nuclear fusion.

Does nature prohibit practical zero-resistance cables that operate at room temperature and run by a mechanism other than superconductivity? Following up on this apparently absurd notion, I will present quantum thermodynamic devices that utilize the strange phenomena occurring at the interface between the quantum and the classical worlds. These devices violate well-accepted laws and rules and enable revolutionary materials and technologies. This colloquium aims not only to inform but also to inspire by posing unanswered questions and suggesting potential paths for future research.

Achieving the science of the extreme universe through developments in gamma-ray instrumentation and telescopes

The New Messengers and New Physics and Cosmic Ecosystem priority themes from the Astro2020 Decadal Survey are uniquely addressed at gamma-ray energies. The gamma-ray group at NASA’s Goddard Space Flight Center, as part of a large effort together with many groups around the world, is developing technologies and future telescopes to enable observations to fill these critical capability gaps revealed by Fermi and fully capitalize on this exciting new era. This talk will present the development of CMOS silicon pixel detectors, called AstroPix, and their planned launch on a sounding rocket; the recent balloon launch of the ComPair gamma-ray prototype telescope; the next steps for ComPair; and community efforts to prioritize gamma-ray missions in the future. 

Thermodynamic Linear Algebra

Linear algebraic primitives are at the core of many modern algorithms in engineering, science, and machine learning. Hence, accelerating these primitives with novel computing hardware would have tremendous economic impact. I'll discuss how a variety of linear algebra problems can be solved by sampling from the thermodynamic equilibrium distribution of a collection of coupled harmonic oscillators. 

Scaling down the laws of thermodynamics

Thermodynamics provides a robust conceptual framework and set of laws that govern the exchange of energy and matter. Although these laws were originally articulated for macroscopic objects, nanoscale systems also exhibit “thermodynamic­-like” behavior – for instance, biomolecular motors convert chemical fuel into mechanical work, and single molecules exhibit hysteresis when manipulated using optical tweezers. To what extent can the laws of thermodynamics be scaled down to apply to individual microscopic systems, and what new features emerge at the nanoscale? I will describe some of the challenges and recent progress – both theoretical and experimental – associated with addressing these questions.  Along the way, my talk will touch on non-equilibrium fluctuations, “violations” of the second law, the thermodynamic arrow of time, nanoscale feedback control, strong system-environment coupling, and quantum thermodynamics.

US Particle Physics for the Next Ten Years

The US particle physics community has gone through a long-range planning exercise for the next ten years. The Particle Physics Project Prioritization Panel (P5) issued a report with recommendations to Department of Energy and National Science Foundation. I discuss how the report defines its scientific scope, what the major initiatives are in the next ten years, derived from a long-term vision for the field. The report also recommends creating a balanced portfolio in the program for all sizes and time scales, domestic vs international, and different subfields.

Topological photonics

There are many intriguing physical phenomena that are associated with topological features --- global properties that are not discernible locally. The best-known examples are the quantum Hall effects in electronic systems, where insensitivity to local properties manifests itself as robust conductance. In this talk, we first discuss how similar physics can be explored with photons; specifically, how various topological models can be simulated in various photonics systems, from ring resonators to photonic crystals and fiber loops. We then discuss how the integration of optical nonlinearity can lead to unique bosonic phenomena, such as topological frequency combs, topological sources of quantum light and chiral quantum optics. These results may enable the development of classical and quantum optical devices with built-in protection for next-generation optoelectronic and quantum technologies.

The Future of Cosmology

Cosmology is currently at a crossroads.  Where do we go  next for  guaranteed science return? The lunar surface allows a unique way forward, to go well beyond current limits in  cosmology. The far side provides a unique radio-quiet environment for probing the dark ages via 21 cm interferometry to seek elusive clues on the building blocks of the galaxies and the nature of inflation. Far-infrared telescopes in cold and dark polar craters will probe the cosmic microwave background radiation back to the first months of the Big Bang. The Moon provides a unique environment for pursuing gravitational wave astronomy and precision optical interferometry.

Democracy, Autocracy and the Threat to Reason in the 21st Century

Please register: https://science.umd.edu/events/milchberg-2024.html

How to Learn to Think Like a Good Physicist and How to Teach It

For many years, my group has been studying what makes up high level performance (“expertise”) in science and engineering (S & E), and how that expertise is best learned and taught.  Being a good physicist primarily involves being able to solve novel authentic physics related problems.  I will discuss how the combination of research on the development of expertise and our recent studies of the nature of S &E problem solving provides guidance for how to best learn that skill.  This learning requires practicing calling on relevant knowledge to make a specific set of decisions that frame the problem-solving process of experts. I will explain how to carry out this practice in the context of physics research and courses, and discuss the research behind this approach. Although the talk will be targeted at physics graduate students, the ideas are very relevant to undergraduates and physics teachers.

High Pressure Quantum Sensing

Pressure alters the physical, chemical and electronic properties of matter. By compressing a material between two opposing brilliant cut diamonds, the diamond anvil cell enables tabletop experiments to reach pressures more than a million times that of atmospheric pressure. Since its development over half a century ago, it has enabled experiments to directly access pressure as a thermodynamic tuning parameter and has had a dramatic impact on quantum science, chemistry and materials physics. Among these impacts, a tremendous amount of recent attention has focused on the discovery of superconductivity in a class of hydrogen-based materials. When compressed to megabar pressures, these so-called super-hydrides are believed to exhibit the highest known critical temperatures, and have led to a nascent field that is equal parts exciting and controversial. Part of this controversy stems from the nature of the tool itself: especially at high pressures, it is tremendously challenging to extract local information from within a diamond anvil cell. 

In this Colloquium, I will describe a new approach to directly "see" the physics inside the science chamber of a diamond anvil cell at ultra-high pressures. The basic idea is deceptively simple: We directly integrate a thin layer of sensors into the surface of the diamond anvil that is actually applying the pressure. I will demonstrate the ability to perform diffraction-limited imaging of both stress fields and magnetism, with the latter allowing us to image the magnetic field expulsion associated with superconductivity. Applying our techniques to cerium hydride, we observe the dual signatures of superconductivity: diamagnetism characteristic of the Meissner effect and a sharp drop of the resistance to near zero. By locally mapping both the diamagnetic response and flux trapping, we directly image the geometry of superconducting regions, showing marked inhomogeneities at the micron scale.

Topology and “impossible” electronic devices

Since the discovery of quantized Hall effects in the 1980s, topology has provided a useful new paradigm for understanding condensed matter systems, expanding our vocabulary for describing the distinctions between states of matter. I will focus on how topological properties can be harnessed to build otherwise impossible electronic devices--devices whose operation, in turn, provides precise tests of the topological description of matter.  In the first example, I will show how a quantized Hall effect can be realized at zero magnetic field from the spontaneous alignment of orbital magnetic moments in a graphene heterostructure. Remarkably, the large magnetic moments of the resulting chiral edge states can be used to realize an electrically actuated magnetic memory, where the macroscopic magnetic moment can be controllably reversed by charging a capacitor. In the second example, I will show how the fractionalization of charge, characteristic of topologically ordered states, can be used to create a purely direct current dissipationless step-up voltage transformer. Along the way, I will introduce the physics of van der Waals heterostructures—layered stacks of atomically thin two-dimensional crystals—and show how the remarkable experimental control available in these systems makes them the leading platform for exploring the interplay of topology and many-body quantum physics, and, potentially, realizing topologically protected quantum bits. 

Observation of Pines’ demon in Sr2RuO4

The characteristic excitation of a metal is its plasmon, which is a quantized sound wave in its valence electron density. In 1965, David Pines predicted that a distinct type of plasmon, which he named a "demon," could exist in multiband metals that contain more than one species of charge carrier. Consisting of electrons in two different bands beating out-of-phase, demons are acoustic excitations, meaning they are “massless,” meaning their energy tends toward zero as the momentum q ® 0. Demons may therefore play a central role in the low-energy physics of multiband metals. However, demons are neutral excitations that do not couple to light, so they have never been observed experimentally, at least in an equilibrium, 3D material. In this talk I will present the observation of a demon in the multiband metal Sr2RuO4. Formed of electrons in the β and γ bands, the demon is gapless with critical momentum qc = 0.08 reciprocal lattice units and room temperature velocity v = 1.065(120)×105 m/s. This study confirms a 67-year old prediction and suggests that demons may be a widespread feature of multiband metals. A. A. Husain, et al., Nature 621, 66 (2023) 

Wielding Quantum Optics for Gravitational Physics

Optical interferometer observatories such as LIGO have begun a new era of astrophysics by measuring the length of their vast arms to such precision that gravitational waves from distant collisions of black holes and neutron stars are now regularly observed. This past run, the global gravitational wave network itself entered a new era, whereby every detector has enhanced sensitivity using quantum squeezed states of light, limited by measurement back-action and optical loss. LIGO is now operating with its "Frequency-dependent squeezing"  upgrade in its ongoing observing run. This technique suppresses back-action from quantum radiation pressure, bypassing trade-offs implied from Heisenberg uncertainty. This talk will: overview squeezing for enhancing astrophysics; introduce Cosmic Explorer, next-generation gravitational wave observatories with deep cosmological reach; and detail the GQuEST experiment at Caltech that hopes to realize different types of quantum enhancements to shed light on experimental techniques where quantum measurement and fundamental physics can collide.

The Quest to See the Invisible with the LUX-ZEPLIN Experiment

LUX-ZEPLIN (LZ) is a multi-tonne scale direct detection dark matter experiment currently being operated at the Sanford Underground Research Facility in Lead, South Dakota. The experiment utilizes a dual-phase time projection chamber (TPC) aided by two veto detectors to primarily look for Weakly Interacting Massive Particles (WIMPs) which are promising dark matter candidates. The active TPC region consists of 7 tonnes of liquid xenon viewed by photomultiplier tubes to record light signals from particle interactions inside the detector. In this talk, I will give an overview of the LZ experiment and discuss its state-of-the-art calibration systems which were designed to ensure a thorough understanding of the light signals produced by its various backgrounds in order to enhance their discrimination and the ability to recognize new signals from potential dark matter particle interactions. I will also discuss LZ first WIMP results and the outlook of the experiment for the future, including a merger with XENON and DARWIN collaborations to build the ultimate Generation-3 dark matter detector.

The Road to Fusion Power with the Centrifugal Mirror

The centrifugal mirror is a magnetic confinement concept that is remarkable for its engineering simplicity compared to other fusion concepts. It consists of a minimum of two circular electromagnets linearly arranged such that the magnetic field between them acts as a potential well that traps the hot plasma that can then be heated to thermonuclear conditions. Plasma heating and stabilization is achieved in the centrifugal mirror by imposing a radial electric field at the axis of the configuration, such that plasma experiences an azimuthal drift that is naturally sheared. This shear in turn leads to viscous heating and prevents the plasma from drifting radially outwards, achieving self-heating and dramatically better confinement than magnetic mirrors without rotation. The Centrifugal Mirror Fusion Experiment (CMFX), a research effort led by UMBC in partnership with the University of Maryland, College Park, has been funded since 2020 by ARPA-E to test the physics of centrifugal mirrors and demonstrate magnetic confinement at parameters relevant to sustained fusion production. The CMFX is the second-generation centrifugal mirror at Maryland, but the first one in the world to use superconducting coils, with a maximum field of 3-T. It is also the first one to achieve sustained operation for up to 10 seconds (limited only by the passive cooling of components). Temperatures, densities, and momentum confinement times in CMFX are now high enough to produce small amounts of fusion energy when experimenting with deuterium plasmas. The success in CMFX has spurred the ongoing engineering design of the next centrifugal mirror machine, led by the commercial spinoff of CMFX, the Terra Fusion Energy Corporation. This new machine will be aimed at demonstrating net energy gain in a small (1 – 10 MWe) modular system that can be used in industrial facilities that require resiliency, such as data centers, and will serve as an intermediate step for systems that can provide 100 MWe or more for regional power generation.

Where is high-energy physics heading to? A viewpoint from CERN

The LHC physics program is advancing successfully and its results have reshaped our views about the particle world. Preparations for the high-luminosity phase of the LHC are in full swing. At the same time, CERN is considering future projects to continue research in the high-energy domain after the LHC. I will review the ongoing decision process and highlight the most promising directions that are currently pursued.  

Physics of Deep Learning

Deep learning has revolutionized fields ranging from image recognition to natural language processing, but its theoretical foundations remain an open frontier. In this colloquium, we will explore how tools and concepts from physics provide a powerful lens for understanding the mechanisms and behavior of deep neural networks, as well as lead to practical engineering advances.

Surprises in Self-Deforming Systems

In classical mechanics we typically study systems that can be represented by point-like particles and are subject to external forcing. In contrast, in living systems we encounter extended objects which undergo internal forcing to generate cyclic changes in shape or configuration. Such dynamics occur across scales, from proteins undergoing conformational changes to cells crawling on surfaces to centipedes wiggling through soil and debris. The physics of such “self-deforming” systems is remarkably rich, especially when coupled to non-trivial environments. In this talk I will narrate a few examples of surprising emergent dynamics in living and nonliving (robot) systems arising from the interplay of traveling waves of body bending and environmental heterogeneities. I will describe how undulatory limbless robophysical models that mix wave and particle-like properties can mechanically “diffract” in regular arrays of obstacles and exponentially localize in disordered environments. Such insights have proven useful in highlighting the importance of mechanics in living systems, e.g. the role of passive dynamics in the locomotion of snakes and nematode worms in heterogeneous environments. Discovery of principles of self-deforming systems is informing and guiding the commercialization of elongate robots (e.g. in a startup company I co-founded) that can self-propel effectively in dirty, dull, and dangerous situations.

Shedding Nano-light on Quantum Materials

Optical spectroscopies have contributed immensely to the present understanding of metals,
superconductors and semiconductors. Unfortunately, optics encounters problems when it comes to “seeing” effects at length scales below the diffraction limit of light and also with probing physics outside of the light cone. Both capabilities are highly desirable for the exploration of quantum physics of new quantum materials. Over the last decade or so, our group has developed and deployed scanning-probe nano-optical methods for the nano-scale spectroscopy and imaging of complex materials. In this talk, I will discuss recent examples of the progress we have made in understanding and controlling the electronic phenomena in quantum materials, all empowered by deeply subdiffractional nano-light.

Photonic Time Crystals and Timetronics

Light-driven nonreciprocal forces in arrays of nano-opto-mechanical oscillators can underpin the functionality of Time Crystals, a many-body interacting system that exhibits a spontaneous mobilization transition to the robust state of oscillation under an infinitely small change of the external driving force.
Such time crystals are a form of Active Matter with life-mimicking dynamics accompanied by the breaking of time translation symmetry, ergodicity, and local entropy decrease. This is of interest to optical “timetronics” – a data processing and communications technology relying on the unique functionalities of time crystals.

Science communication and miscommunication

Science is by the people and for the people. But the people doing science don’t always have an easy time making themselves understood by the rest of the people. I will discuss why science communication is important, give some examples of dramatic misunderstandings of science by the general public, share my personal journey through science communication, and give some advice to early career researchers enthusiastic about communicating with the public. 

From arXiv to 'story's live': How physics gets reported in the press

Physics journalism is often a mystery to its primary subjects: physicists. In this talk I will try to demystify physics journalism by discussing the principles and processes that physics journalists use. I'll break down the stages of reporting a story, from conceptualization to publication, and I'll explain what different parts of a story do and how they are constructed. I will also disclose aspects of my own process—emails, interview notes, and rough drafts—to help explain specific editorial choices. As case studies to illustrate the practice of physics journalism, I will use one news story and one feature story, both about an exciting new development in fundamental physics: the observation of the fractional quantum anomalous hall effect (FQAHE) in moiré quantum materials. 

Quantum Signal Processing: Making Schrödinger Cats and Other Exotic States of Microwave Photons

The Schrödinger Cat idea was an early thought experiment intended to point out the weirdness of quantum mechanics. It is a paradigmatic example of the quantum principles of superposition and entanglement. With the vast experimental progress in the last two decades, we can now routinely carry out this experiment in the laboratory. In this pedagogical talk, I will present a ‘quantum signal processing’ recipe for how to create a Schrödinger Cat in a system consisting of a superconducting microwave resonator (a harmonic oscillator) and a superconducting qubit (a two-level artificial atom). Extensions of this recipe now allow us to create even more exotic states of microwaves that can be used as quantum error correction codes.

Communicating What Science Knows in a Polarized Time

The talk will explore ways to reduce resistance to knowledge about topics ranging from arctic sea ice extending to vaccination safety.   

 
Kathleen Hall Jamieson is the Elizabeth Ware Packard Professor at the Annenberg School for Communication of the University of Pennsylvania, the Walter and Leonore Annenberg Director of the university’s Annenberg Public Policy Center, and Program Director of the Annenberg Foundation Trust at Sunnylands. She has authored or co-authored 18 books, including Democracy Amid Crises: Polarization, Pandemic, Protests, and Persuasion (2023) with the Annenberg IOD Collaborative, Creating Conspiracy Beliefs: How Our Thoughts Are Shaped (2022), and Cyberwar: How Russian Hackers and Trolls Helped Elect a President, which won the Association of American Publishers' 2019 R.R. Hawkins Award. Six of the books that Jamieson has authored or co-authored have received a total of 12 political science or communication book awards (Cyberwar, Packaging the Presidency, Eloquence in an Electronic Age, Spiral of Cynicism, Presidents Creating the Presidency, and The Obama Victory). She co-edited The Oxford Handbook of Political Communication and The Oxford Handbook of the Science of Science Communication.

In 2020, the National Academy of Sciences awarded Jamieson its Public Welfare Medal for her “non-partisan crusade to ensure the integrity of facts in public discourse and development of the science of scientific communication to promote public understanding of complex issues.” In 2022, the Roper Center for Public Opinion Research awarded Jamieson the Warren J. Mitofsky Award for Excellence in Public Opinion Research. In 2023, Jamieson was elected to the Board of Directors of the American Association for the Advancement of Science (AAAS). Jamieson is a member of the American Philosophical Society and the National Academy of Sciences, and a Distinguished Scholar of the National Communication Association. She also is a fellow of the American Academy of Arts and Sciences, the AAAS, the American Academy of Political and Social Science, and the International Communication Association, and a past president of the American Academy of Political and Social Science.

Jamieson has won university-wide teaching awards at each of the three universities at which she has taught and has delivered the American Political Science Association’s Ithiel de Sola Pool Lecture, the National Communication Association’s Arnold Lecture, the NASEM Division of Behavioral and Social Sciences and Education's Henry and Bryna David Lecture, and the keynote lecture at the CDC's Charles C. Shepard Science Awards (2022). Her paper “Implications of the Demise of ‘Fact’ in Political Discourse” received the American Philosophical Society’s 2016 Henry Allen Moe Prize. She is the co-founder of FactCheck.org and its SciCheck project, and director of The Sunnylands Constitution Project, which has produced more than 30 award-winning films on the Constitution for high school students.

Opportunities of Photonics at Nanoscale

The interaction of light with nanostructures provides numerous opportunities for exploring fundamental physics using light, and has profound implications for technological developments. In this talk, we will discuss some of our recent efforts in exploring the fundamental science of nanophotonics, and in exploiting some of these fundamental advances for information and energy technology applications.

Shanhui Fan is the Joseph and Hon Mai Goodman Professor in the School of Engineering, a Professor of Electrical Engineering, a Professor of Applied Physics (by courtesy), and a Senior Fellow of the Precourt Institute for Energy, at the Stanford University. He received his Ph. D in 1997 in theoretical condensed matter physics from the Massachusetts Institute of Technology (MIT). His research interests are in fundamental studies of nanophotonic structures, especially photonic crystals, plasmonic structures, and meta-materials, and applications of these structures in energy and information technology applications. He has published over 700 refereed journal articles, has given over 400 plenary/keynote/invited talks, and holds over 70 US patents. He is a co-founder of two companies aiming to commercialize high-speed engineering computations and radiative cooling technology respectively.  Prof. Fan received a National Science Foundation Career Award (2002), a David and Lucile Packard Fellowship in Science and Engineering (2003), the U. S. National Academy of Sciences W. O. Baker Award for Initiatives in Research (2007), the Adolph Lomb Medal from the Optical Society of America (2007), a Vannevar Bush Faculty Fellowship from the U. S. Department of Defense (2017), a Simons Investigator in Physics (2021), and the R. W. Wood Prize from the Optica (2022).  He is a member of the U. S.  National Academy of Engineering, and a Fellow of the IEEE, the American Physical Society, the Optica, and the SPIE.

https://profiles.stanford.edu/shanhui-fan

Black Holes, Quantum Mechanics, and the Emergence of Space and Time

Quantum mechanics is the theory which governs the behavior of matter at the atomic scale, but so far we have not succeeded in making it compatible with gravity.  This tension is highlighted by Stephen Hawking's famous "black hole information paradox", which argues that any self-consistent combination of quantum mechanics and gravity must violate some fundamental principle of physics.  In recent years consensus has been building that the principle which must be given up is the existence of spacetime as a fundamental entity: instead space and time are emergent notions, valid only in certain situations and only in some approximation.  What does it mean for space and time to be emergent?  When can they fail to emerge and how badly?  In this talk I will give a broad overview of these ideas, building towards recent developments which put the emergence of spacetime on a firm mathematical footing by relating it to ideas from the theory of quantum computation. 

Daniel Harlow is an Associate Professor of Physics at MIT, working on quantum aspects of black holes and cosmology.  He grew up in some combination of Cincinnati, Boston, and Chicago, and attended Columbia University (BA) and Stanford University (PhD). Harlow received the New Horizons in Physics Prize in 2019 "for fundamental insights about quantum information, quantum field theory, and gravity.” He is an avid hiker and pianist. 

Experimental Studies of Black Holes: Status & Prospects

More than a century ago, Albert Einstein presented his general theory of gravitation. One of the predictions of this theory is that not only particles and objects with mass, but also the quanta of light, photons, are tied to the curvature of space-time, and thus to gravity. There must be a critical mass density, above which photons cannot escape. These are black holes. It took fifty years before possible candidate objects were identified by observational astronomy. Another fifty years have passed, until we finally can present detailed and credible experimental evidence that black holes of 10 to 10¹⁰ times the mass of the Sun exist in the Universe. Three very different experimental techniques have enabled these critical experimental breakthroughs. It has become possible to investigate the space-time structure in the vicinity of the event horizons of black holes. I will summarize these interferometric techniques, and discuss the spectacular recent improvements achieved with all three techniques. In conclusion, I will sketch where the path of exploration and inquiry may lead to in the next decades.

Reinhard Genzel, born 1952 in Bad Homburg v. d. H., Germany, is one of the Directors of Max Planck Institute for Extraterrestrial Physics, Professor in the Graduate School of the University of California, Berkeley and an Honorary Professor at the Ludwig Maximilian University, Munich. He is a Scientific Member of the Max Planck Society and a member of the US National Academy of Sciences. His research interests include astrophysics of galactic nuclei, star formation, kinematics and cosmic evolution of galaxies, massive black holes and experimental infrared, submillimeter and millimeter astronomy. He has received numerous honours and awards, including the Shaw Prize of The Shaw Prize Foundation and the Crafoord Prize in Astronomy. In 2020, he received the Nobel Prize in Physics, jointly with Andrea Ghez, for the discovery of a supermassive compact object at the centre of our galaxy.

https://science.umd.edu/events/genzel.html

Relativistic optics and laser-driven particle accelerators

The remarkable increase in peak laser intensity over the past 30+ years –over 6 orders of magnitude--has spurred new and exciting advances in laser-driven sources of relativistic charged particles and light, along with the new field of indestructible plasma optics. I will start with our recent results demonstrating acceleration of electrons up to 10 GeV in just 30 cm—a distance 5,000 times smaller than required using conventional technology, and then work backward to highlight the physics building blocks that made such a result possible.

Jonathan Bagger, American Physical Society

This year, 2024, marks the 125th anniversary of the founding of APS.  To recognize the occasion, the APS Board refreshed the Society’s mission, vision, and core values.  It also endorsed a strategic framework to guide APS in the years ahead.  In this talk, I will introduce the Society.  I will explain what it is, where it is going, and most importantly, why we should care.

Challenges and Opportunities in Communicating STEM

This talk aims to explore twin universal concerns in communicating scientific work, for any audience. For one, we will describe and demonstrate elements of craft: distilled, actionable lessons from professional writers translated and applied to the unique challenges we face in relaying complex technical projects. These elements include familiar obstacles like jargon but also less familiar opportunities like basic narrative tension. For another, we will explore calibration: research from cognitive science and human brain evolution can serve us well in considering our audiences with savvy compassion. In sum, the talk seeks to improve the clarity, impact, and persuasive power of our work, with hopes of benefiting scientists and engineers at any stage of their careers.

Scaffold and Arch: From Dispersion Theory to Matrix Mechanics*

Students of quantum mechanics interested in the history of their field are likely to be baffled by the Umdeutung (= reinterpretation) paper with which Heisenberg laid the basis for matrix mechanics in the summer of 1925. In Dreams of a Final Theory, Steven Weinberg confessed that he had never understood this paper. In an interview in the 1960s, Alfred Landé, a contemporary of Heisenberg, put it more bluntly: “Heisenberg stammered something, Born made sense of it.” And, indeed, the so-called Dreimännerarbeit (= Three Man Paper) of late 1925/early 1926, in which Born, Heisenberg and Jordan gave the first systematic exposition of matrix mechanics poses no particular difficulties for those familiar with the basics of quantum mechanics. In this talk, I will argue that the reason the Umdeutung paper, by contrast, looks so mysterious to modern eyes is that it still shows many traces of the scaffold on which it was built, a lengthy paper on the Kramers dispersion theory that Heisenberg co-authored with Kramers in late 1924/early 1925. Since the dispersion-theory scaffold is no longer visible today, admirers of the matrix-mechanics arch built on top of it are left wondering how this arch was originally erected.

*Based on joint work with Anthony Duncan (Department of Physics and Astronomy, University of Pittsburgh)

The Next Generation of Neutrino Astrophysics with PUEO

Neutrinos provide a unique window into the highest energy accelerators in the Universe. Due to only interacting weakly, they are capable of traveling directly from their sources to detectors built on Earth. They are ideal candidates for unraveling the mysteries of the ultra high energy cosmic ray flux and understanding particle physics at energies beyond the capabilities of detectors on Earth.

In this talk, I will provide an overview of past, present, and future astrophysical neutrino detectors, with specific focus on the Payload for Ultrahigh Energy Observations (PUEO), a new experimental effort that will fly out of Antarctica in December 2025. I will discuss how updates to the trigger and instrument make PUEO a discovery instrument. And finally, I will talk about how PUEO fits into the larger field of neutrino astrophysics

The Quantum Reform of the Modern Metric System:  Mass becomes quantum, and electrical measurements become honest

The modern metric system, officially known as the International System of Units (SI), has recently undergone its most revolutionary change since the inception of the metric system at the time of the French revolution.  The kilogram, ampere, kelvin, and mole all have new definitions, based on fixing the values of fundamental constants of nature.  Famously, the reform eliminates the artifact International Prototype Kilogram as the foundation of the unit of mass.  This lecture will explain why this was necessary and how it was accomplished.  Less famously, the century-old practice of having two separate unit systems for electrical metrology —“legal” and “scientific”— has disappeared with the reformed SI.    

https://ireap.umd.edu/events/paint-branch-distinguished-lecture-applied-physics-2024

Asymptomatic: The Silent Spread of COVID-19 and the Future of Pandemics

This talk explores an idea and its consequences. The first part leverages dynamical principles and public health data to explain how COVID-19's ability to silently spread between individuals often without causing illness is precisely what made it catastrophic for society as a whole. The second part looks ahead and identifies model-informed public health approaches that can effectively reduce asymptomatic transmission so as to prevent and control future pandemics.

PRX: What Kind of Papers We are Looking for?

PRX is published by the American Physical Society, a nonprofit membership society of scientists.  Its mission goal is to select around 250 *landmark* papers a year from all fields of physics and showcase them to a broad and multidisciplinary readership.  Is your paper a good match for PRX?  Or asked differently, what papers qualify as *landmark* papers?  How do the PRX editors actually select such papers?  Are such selections always accurate?How can you, as an author, navigate PRX’s editorial and peer-review process effectively and get the most out of your interactions with the editors and referees? I will use the talk to discuss with you how to answer these questions.  Many of these questions do not have a black-and-white answer in the case of a single paper.  Open-minded, reasoned, and constructive dialogues amongst the authors, the editors, and the referees are key to making each concrete process a meaningful and productive experience, and sometimes even a pleasure, for everyone.

Neutrino Astronomy: Viewing the High Energy Sky Through the South Pole Glacial Ice

This talk will summarize recent advances in the ongoing quest to view the universe at higher energies to identify the sources of the highest energy cosmic rays and to elucidate the astrophysical mechanisms at work in these extreme objects. I explain why neutrinos, nearly massless neutral elementary particles, are the perfect “messenger” particles, which enable us to both extend the energy range at which we can view the distant universe and to unambiguously identify sources of high energy cosmic rays. While the concept of a neutrino telescope is many decades old, the means to build such a telescope at the needed 1 cubic-kilometer scale remained technically elusive until the international IceCube collaboration successfully deployed the first such instrument in the glacial ice located at the Antarctic South Pole station. The IceCube Neutrino Observatory is comprised of over 5,000 highly sensitive photodetectors imbedded to a depth of 2.5 kilometers instrumenting a cubic kilometer of optically clear ice and began full operations in 2011. The IceCube detector has recorded neutrinos at energies over 1 PeV or about 10 15 times the energy of visible light photons, opening a new window into the high energy extreme universe for the first time. This new glimpse of the universe at these extreme energies has revealed the first ever neutrino sources, and our first unambiguous detection of high energy cosmic ray sources outside our galaxy. Recently the IceCube neutrino telescope has also given us our first view of the galactic plane in neutrinos. This talk will present an overview of these results. I will close with a brief description of what these first measurements tell us about the neutrino sky, and the
plans to build a next generation telescope with higher sensitivity.

The Mathematics of Human Population Growth and CO2 Emissions

In a paper published in the Science magazine in 1960, von Foerster et al. argued that human population growth follows a hyperbolic pattern with a singularity in 2026. Using current empirical data from 10,000 BCE to 2023 CE, we re-examine this claim. We find that human population initially grew exponentially as N(t)~exp(t/T) with T=3050 years. This growth then gradually evolved to be super-exponential with a form similar to the Bose function in statistical physics. Population growth further accelerated around 1700, entering the hyperbolic regime N(t)=C/(ts-t) with the projected singularity year ts=2030, which essentially confirms the prediction by von Foerster et al. We attribute the switch from the super-exponential to the hyperbolic regime to the onset of the Industrial Revolution and the transition to massive use of fossil fuels. This claim is supported by a linear relation that we find between population and the increase in the atmospheric level of CO2 from 1700 to 2000. But in the 21st century, the inverse population curve 1/N(t) deviates from a straight line and avoids crossing zero, thus escaping a literal singularity. We find that N(t) is well fitted by the square root of the Lorentzian function, with a maximum of about 8.2 billion people at t=ts. The width 2\tau of the population peak is given by the cutoff time \tau=32 years. We also find that the increase in the atmospheric CO2 level since 1700 is well fitted by arccot[(ts-t)/\tau_F] with \tau_F=40 years. This fit gives a forecast of the CO2 level in the near future for the 21st century.

Fast and Flexible Group Decision-Making

A wide range of animals live and move in groups. Many animals do better in groups than alone when, for example, foraging for food, migrating, and avoiding predators. A key to group success is social interaction. Less well understood is how a group, with no centralized control, is capable of the fast and flexible decision-making required to carry out its tasks in an environment with uncertainty, variability, and dynamic change.

I will introduce an approach to modeling group decision-making dynamics that reveals the fundamental importance of nonlinearity, feedback, and social interaction. Analysis of the model provides new insights into fast and flexible decision-making: how indecision can be broken as fast as it becomes costly, and how sensitivity to stimulus can be tuned as context and environment change. I will discuss the significance of these results for the study and design of collective intelligence in nature and technology. 

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