JILA Auditorium

Abstract: The scales of asteroid strength, from centimeters to tens of meters or more, can in principle be connected via the well-known Weibull theory (Weibull 1951) that explains in probabilistic terms why small samples of a rock are stronger than the whole. There are fewer weak flaws to be exploited in a smaller sample. This leads to a statistical understanding of size-dependent strength that has been implemented in fragmentation and damage models for planetary materials (Melosh et al., 1992; Benz and Asphaug 1994, 1995). The Weibull analysis enabled Cotto-Figueroa et al.

Abstract: The most basic requirement of a scientific theory is that it make predictions. Is the Standard Model a scientific theory? As the well-tested, reigning theory of the elementary particles and fundamental forces, the Standard Model certainly claims to be able to predict the outcomes of a wide range of experiments. Yet from inelastic nuclear scattering, to neutron stars and superconductors, the universe is filled with systems whose behavior should be predicted by the Standard Model, but for which no such predictions are forthcoming!

Abstract: The 2025 Nobel Prize in Physics was awarded to John Clarke, Michel Devoret, and John Martinis “for the discovery of macroscopic quantum mechanical tunnelling and energy quantization in an electric circuit.”  This talk will give a brief history of their work and the remarkable developments that followed from it.

Linear spectroscopy is used to learn about transitions from the ground states of systems. Nonlinear spectroscopies, such as transient absorption (TA) spectroscopy, first excite the system and then probe after some time delay, giving dynamical information about excited states and spectral information about their excitations. If the pump pulses are strong enough, then some molecules are excited multiple times, and the signal has contributions from singly excited molecules mixed with those from multiply excited molecules.

Abstract: Modeling gas-phase chemical kinetics relevant to combustion and atmospheric chemistry requires a complete description of elementary reactions involving ephemeral species such as hydroperoxyalkyl radicals, Q̇OOH, which undergo competing sets of unimolecular reactions and bimolecular reactions with O2. The balance of flux from the competition affects rates of chain-branching and inherently depends on temperature, pressure, and oxygen concentration.

Quantum interferences, where two electronic pathways “compete” in a manner akin to the interference of separate propagating waves, are often exploited in atomic systems to realize a variety of exotic phenomena, such as electromagnetically induced transparency, slow light and lasing without inversion. In crystalline materials, quantum interferences can sometimes be difficult to discern with conventional probes, even if their consequences may be just as profound.

Abstract: Understanding thermal transport and light-matter interactions at the extreme scales is both fundamentally important and practically relevant. Studying these regimes often demand new instrumentation and high-resolution sensing techniques. In this talk, I will present my lab’s efforts to explore the complex landscape of heat transport and nanophotonics at the atomic and single-molecule scale. Specifically, we have developed microfabricated scanning thermal microscopes with picowatt- and sub-picowatt sensitivity and atomic spatial resolution.

Abstract: Magnetism is a striking example of how quantum mechanics and interactions among electrons combine to generate entirely new forms of collective behavior—phenomena that deepen our understanding of matter, as well as power modern technologies. Over the past decades, discoveries in magnetism have often heralded new paradigms in condensed matter physics, exemplified by antiferromagnetism and Mott insulators, and quantum spin liquids with their fractionalized excitations. In real materials, however, spins are inseparable from the crystalline lattices that host them.

The corona is a layer of hot plasma that surrounds the Sun, traces out its complex magnetic field, and ultimately expands into interplanetary space as the supersonic solar wind. This complex and unpredictable system varies over many orders of magnitude in space and time, so it's not surprising that we still do not have a complete theoretical understanding of its origins. In this talk, I will present some new observations and theoretical concepts that are helping us get closer to finally identifying and characterizing the physical processes responsible for the corona and solar wind.

Abstract: With the advent of the Gaia space mission, there has been a revolution in astronomers’ ability to precisely locate the interstellar structures the Sun may have encountered on its voyage around the galaxy. We now have the spatial resolution to trace the Sun’s trajectory back through its interstellar environment up to 60 million years in the past (4000 light-years in distance). This timescale is commensurate with the timescale over which we can reconstruct the paleoclimate of Earth from deep ocean foraminiferas.