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Colloquia are Wednesdays at 4:00 p.m. in the JILA Auditorium.��

Coffee, tea and cookies will be available in G1B31 (across from G1B20) from 3:30 - 3:50 p.m.

January 15 — "Toward Quantum Imaging of Nuclei"

• Presenter: Miguel Arratia, University of California, Riverside
• Host: Jamie Nagle
• Abstract: The atomic nucleus emerges from interacting quantum particles called quarks and gluons, but how this happens remains unknown. This might be elucidated with quantum-level "images" of their position, orbital motion, spin alignment, and entanglement. I will describe recent and upcoming experiments at the Thomas Jefferson Laboratory that use a high-intensity, high-energy electron beam to probe a wide range of nuclear targets, from polarized lithium to lead. I will also explain how these studies pave the way for future research at the Electron-Ion Collider (EIC), which will usher in a new era by providing a novel tool: particle jets. To advance EIC jet physics, we are developing next-generation, highly granular calorimeter systems, which can be enhanced with state-of-the-art AI/ML methodologies. I will summarize recent prototype testing conducted at various facilities and discuss plans for further testing and construction in the near future.

January 22 — "Economic inequality from a statistical physics point of view"

• Presenter: Victor Yakovenko, Physics and JQI, University of Maryland, College Park
• Host: Rahul Nandkishore
• Abstract: Inequality is an important and seemingly inevitable aspect of the human society. Various manifestations of inequality can be derived from the concept of entropy in statistical physics.��In a stylized model of monetary economy, the probability distribution of money among the agents converges to the exponential Boltzmann-Gibbs law due to entropy maximization. Our analysis of empirical data shows that income distributions in the USA and other countries exhibit a two-class structure. The lower class (about 97% of population) is characterized by the "thermal" exponential distribution, whereas the upper class (about 3%) by the "superthermal" Pareto power law.��The total income share of the upper class expands and contracts dramatically during booms and busts in financial markets.��We also found that global inequality in energy consumption and CO₂ emissions has been decreasing since 1980 (likely due to the globalization) and converging toward the exponential distribution. The decrease in global inequality stopped recently, when maximal entropy was reached, as we predicted in advance.��All papers are available at

January 29 — "�����ɴǰ��������ڰ��dz�����������������Ǵ����貹����"

• Presenter: Tadashi Tokieda, Stanford University
• Host: Leo Radzihovsky

• Abstract: Starting from just a sheet of paper, by folding, stacking, crumpling, sometimes tearing, we will explore a diversity of phenomena, from magic tricks and geometry to elasticity and the traditional Japanese art of origami. Much of the lecture consists of table-top demonstrations, which you can try later with friends and family.

  So, take a sheet of paper . . .

• Bio: Tadashi Tokieda is��a��professor at Stanford University. He grew up��as��a��painter in Japan, became��a��classical philologist (not to be confused with philosopher) in France��and, having earned��a��PhD in pure mathematics��from��Princeton, has been��an��applied mathematician in England��and the US. He is��also��active in outreach in the developing��world, especially via the��African Institute for Mathematical Sciences (AIMS)��as well��as the YouTube channel Numberphile. Tokieda was invited to deliver��a��public lecture��at the 2018 ICM��and��at the 2022 ICM.

**Special Colloquium** Monday, February 3 — "A view into the flow and fracture of glacier ice"

• Presenter: Joanna Millstein, Colorado School of Mines
• Time: 11:00 a.m.
• Location: JILA Auditorium
• Host: Mike Ritzwoller
• Abstract: Glaciers deform through the driving force of their own weight and display dramatic responses to both external forcing, such as changes in climate, and internal forcing like variations in stress. Determining the response of glaciers and ice sheets to such forcing was, until very recently, limited by sparse observations and data across the cryosphere. The rapid expansion of pertinent and available satellite-based data has created an opportunity to understand the processes contributing to dynamic change through melting and calving, the fracture of icebergs. I leverage the expanding volume of satellite observations to develop and refine models of ice flow and ice fracture through mechanical and statistical frameworks. In this talk, I will discuss a modern reexamination of the constitutive law for glacier ice and new parameterizations for large ice fractures. These observational studies improve higher-order ice sheet models, enabling a more complete view of ice sheet change. This research showcases the power of quantifying and calibrating the processes of ice flow and ice fracture to understand ice sheet stability and to assess future projections of glaciers and ice sheets in a changing climate.

February 5 — "Tabletop X-Ray Lasers: From Star Wars to Quantum Sculpting"

• Presenter: Margaret Murnane, JILA, University of Colorado, Boulder
• Host: Tobin Munsat
• Abstract: Ever since the invention of the laser over 60 years ago, scientists have been striving to create x-ray lasers. In the same way that visible lasers can concentrate light energy far better than a light bulb, a directed beam of x-rays would have many useful applications. The problem was that until recently, ridiculously high powers were needed to make an x-ray laser. Some of the first x-ray lasers were powered by nuclear detonations as as part of the “star wars” program in the 1980s. To make a practical, tabletop-scale, x-ray laser source required taking a very different approach. The story behind how this happened is surprising, where we learned how to transform ultrafast laser light into directed beams of x-rays by sculpting the wave function of a radiating electron. Along the way, we also learned to generate the shortest strobe light in existence, and to build near-perfect short wavelength microscopes.

**Canceled** February 12 — "Quantum Simulation and Sensing with Atoms Interacting via Photons"

• Presenter: James K. Thompson, JILA, NIST, University of Colorado, Boulder
• Host: Ana Maria Rey
• Abstract: Photons bouncing back and forth many times between mirrors provide a way for atoms to interact at essentially infinite range. ��These interactions open powerful new paths for quantum simulation and quantum sensing, allowing us to leverage the certainty provided by quantum mechanics to make very precise measurements of the world around us, or allowing us to emulate one quantum system with another to provide insights and understanding. In this talk, I will provide a sampling of my group’s work including how we use the quantum measurement process and interactions to create some of the most highly-entangled states realized in any system, realize the first entanglement-enhanced matterwave interferometer, and simulate the predicted dynamical phases of BCS superconductors.

**Special Colloquium** Monday, February 17 — "The Role of Clouds in Earth’s Changing Climate"

• Presenter: Ivy Tan, McGill University
• Time: 11:00 a.m.
• Location: JILA Auditorium
• Host: Michael Ritzwoller
• Abstract: How much will Earth warm in response to increasing carbon dioxide emissions?�� Climate projections are highly uncertain yet have important societal implications.�� Climate models are the most effective tools for making climate projections, however, their ability to reliably project climate has been hindered primarily by challenges in representing clouds in Earth’s atmosphere.�� Cold clouds composed of supercooled liquid droplets and ice crystals are particularly challenging to represent in climate models due to the large number of complex micro-scale physical properties and processes associated with these clouds.�� In this talk, I will demonstrate how satellite observations are indispensable tools for improving our understanding of cloud physical processes and improving the representation of these processes in climate models.�� I will also identify the key micro-scale physical processes associated with cold clouds that are important for Earth’s changing climate through their interactions with solar and terrestrial radiation.�� I will then focus on clouds in the Arctic --- a region where Earth is experiencing accelerated warming compared to the rest of the globe -- and show how nonlinear interactions between clouds, the vertical thermal structure of the atmosphere, and sea ice contribute to the amplified warming.�� I will conclude with a glimpse into exciting new developments underway, including the future launch of satellite instruments and the rise of high-resolution global storm-resolving models, and explain how these advancements will enhance our understanding of Earth’s physical climate system in the coming decade.

February 19 — "Closing the Loop in Early Universe Cosmology?"

• Presenter: Chris Smeenk, Western University, Canada
• Host: Allan Franklin
• Abstract: Inflationary cosmology has been widely accepted for decades. Yet there are persistent debates about inflation which raise central questions in philosophy of science. Skeptics have often expressed doubt regarding whether inflation is "testable" or "falsifiable," due to the flexibility of inflationary models. This is an instance of a general question in philosophy of science: to what extent does phenomenological success support the claim that a theory gets the physics right? How does one answer a skeptical worry, that the theory "fits the data" because it is flexible? My aim in this talk is reframe this debate, drawing on ideas from George Smith’s historical and philosophical assessment of celestial mechanics. Smith answers the skeptic by looking at the role a theory plays in guiding inquiry. Following Newton, astronomers "closed the loop" by starting with an initial description of motions; using discrepancies with observations to identify sub-dominant physical details; incorporating these details into a more refined description; and then starting the process over again. Through this process astronomers discovered hundreds of new details about the solar system, based on assuming the theory of gravity, that could be checked independently. Considering this case helps to characterize one challenge facing theories of the early universe: our lack of clarity about the underlying physics driving inflation has blocked pursuit of a similar process of iterative refinement. I will close by considering several different responses to this challenge.

**Special Colloquium** Thursday, February 20 — "Decoding the Dialogue Between Clouds and Land through Boundary-Layer Turbulence"

• Presenter: Tianning Su, Lawrence Livermore National Laboratory
• Time: 11:00 a.m.
• Location: JILA Auditorium
• Host: Michael Calkins
• Abstract: The planetary boundary layer (PBL), the lowest part of the atmosphere, plays a key role in regulating interactions between the land surface, clouds, and atmospheric turbulence. These interactions drive the exchange of energy, moisture, and aerosols, shaping both weather and climate. However, turbulence within the PBL adds complexity to these processes, making them challenging to understand and predict. In this seminar, I will examine how PBL turbulence mediates the "dialogue" between clouds and land, with a focus on the role of surface fluxes and radiation in regulating the coupling between them. Using lidars—laser-based instruments that detect atmospheric particles such as aerosols and clouds—we developed remote sensing algorithms to determine PBL height and cloud properties, offering observational evidence into the mechanisms that drive aerosol transport and cloud formation. These observations help us investigate how cloud-land coupling influences aerosol-cloud interactions, which remain one of the largest uncertainties in climate projections. Finally, I will discuss how these findings inform climate models, with support from artificial intelligence to integrate complex data and refine simulations. By integrating high-resolution field observations with advanced modeling, this research deepens our understanding of how PBL turbulence shapes interactions between clouds and land, a key driver of weather patterns and the climate system.

**Special Colloquium** Monday, February 24 — "Turbulent and stochastic dynamics in the climate system: energy transfers, self-organization and abrupt transitions"

• Presenter: Adrian Van Kan, University of California, Berkeley
• Time: 11:00 a.m.
• Location: JILA Auditorium
• Host: Michael Calkins
• Abstract: The Earth’s climate system is highly complex, consisting of many coupled components. Turbulent motions in the atmosphere and oceans across a wide range of spatial and temporal scales are highly important as they not only transport heat from the equator to the poles, but also distribute aerosols, nutrients and pollutants across the globe. These atmospheric and oceanic fluid flows are impacted at large scales by the Earth’s rotation, density stratification and their thin-layer geometry - for instance, the troposphere is around 10km high, but weather systems typically extend over 1000km in the horizontal direction. These factors strongly constrain the behavior of these flows, leading to striking self-organization into large-scale vortices and zonal jets. Moreover, nonlinear feedback mechanisms in this complex system lead in many cases to multiple coexisting metastable states, between which the system can transition abruptly due to intrinsic fluctuations or external (e.g., anthropogenic) forcing. An important example of this is the Atlantic Meridional Overturning Circulation, which is a tipping element in the climate system that has been abruptly shut down and re-emerged in the past. Due to the complexity of the climate system, a hierarchy of models of varying complexity is required to elucidate its properties. In this talk, I will present results from idealized models at the lower-complexity end of this model hierarchy,��where key physical insights can be gleaned, namely self-organization in a turbulent dry atmosphere and abrupt transitions between large-scale, hurricane-like vortices and zonal jets or small-scale three-dimensional turbulence. I will also provide an outlook on my future work, including rotating moist convection, which is a key driving mechanism in Earth’s atmosphere, idealized climate modeling and ideas relating to climate engineering.

February 26 — "An introduction to climate engineering"

• Presenter: David Keith, University of Chicago
• Host: Eric Cornell
• Abstract: It is possible to reduce some of the climate risks of accumulated CO₂ by deliberately altering the Earth's albedo using Sunlight Reflection Methods (SRM) also called solar geoengineering. It is possible to remove carbon from the atmosphere at large scale using various methods for Carbon Dioxide Removal (CDR).�� Estimates of the cost, risks, and efficacy of these tools will remain uncertain but it is now possible to make some policy-relevant quantitative comparisons between risks and benefits, and to speculate about the appropriate use of energy-system decarbonization, CDR, and SRM.

**Special Colloquium** Thursday, February 27 — "Oceanic turbulence regimes and their impact on the climate system"

• Presenter: Roy Barkan, Tel Aviv University
• Time: 11:00 a.m.
• Location: JILA Auditorium
• Host: Michael Ritzwoller
• Abstract: The ocean absorbs most of the heat and about a quarter of the carbon emissions caused by human activities. These anthropogenic perturbations significantly influence the ocean circulation, with direct and critical implications for the climate system. The ocean circulation is characterized by diverse turbulence regimes that span a vast range of spatial and temporal scales. Understanding how these distinct turbulence regimes and their interactions lead to the observed spatiotemporal distributions of energy, heat, and tracers in the ocean is essential for predicting circulation adjustments and their effects on the climate system.��
  In this talk, I will discuss how the interplay between geostrophic turbulence, submesoscale turbulence, boundary layer turbulence, and wave turbulence shapes the ocean circulation, with a particular focus on energy transfer and material transport. I will also distinguish between the dominant processes occurring in the ocean’s mixed layer, where continuous interactions with the atmosphere take place, and in the deeper thermocline region. Finally, I will demonstrate how a comprehensive approach – combining analytical theory, circulation models of varying complexity, remote sensing, and carefully designed field experiments – can ultimately improve the representation of these turbulent processes in climate models.

March 5 — "From Mars Sample Return to Enceladus plume missions: finding habitable environments and life across the solar system"

• Presenter: Jonathan Lunine, JPL, Caltech
• Host: Mihaly Horanyi
• Abstract: Planetary exploration has unveiled environments that could support life today, or in the past, or contain the ingredients of life. Mars was once habitable; Enceladus’ ocean is today, Europa is a question mark, and Bennu contains most of the basic key monomers of life in abiotic form. I will discuss how this all fits together.��

March 12

• Presenter: Holger Mueller, Berkeley
• Host: Adam Kaufman
• Abstract:

March 19��

• Presenter: Merav Opher, Boston University
• Host: Mihaly Horanyi
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March 26 — No Colloquium, Spring Break

April 2

• Presenter: Martin Formanek, MPIK, Heidelberg, Germany
• Host: Yuan Shi
• Abstract:

April 9

• Presenter: Alireza Marandi, Caltech
• Host: Juliet Gopinath
• Abstract:

April 16

• Presenter: Sébastien Corde, Ecole Polytechnique
• Host: Michael Litos
• Abstract:

April 23

• Presenter: Chunmei Ban, University of Colorado, Boulder
• Host: Joe Berry
• Abstract:

April 30

• Presenter: Steve Girvin, Yale
• Host: Leo Radzihovsky
• Abstract:

For more information about colloquia this semester, contact: Mihaly Horanyi