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

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

August 28Ìý— "Optical nuclear clock: nuclear physics meets metrology"

  • Presenter: Chuankun Zhang, JILA
  • Host: Jun Ye
  • Abstract:ÌýLaser-based measurement and control of atomic and molecular states form the foundation of modern quantum technology and provide deep insights to fundamental physics. The recent breakthrough of quantum-state-resolved thorium-229 nuclear laser spectroscopy marks the beginning of precision metrology for nuclear transitions. Using a state-of-the-art frequency comb in the vacuum-ultraviolet, we coherently excite the thorium nuclear clock transition and link its frequency directly to today’s most precise atomic clock based on strontium-87. This unification of precision metrology and nuclear physics sparks new ideas for fundamental physics tests and promises nuclear-based robust timing applications.

September 4Ìý— "Ergodicity breaking in quantum dynamics"

  • Presenter: Rahul Nandkishore, ÀÖ²¥´«Ã½ Boulder
  • Host:Tobin Munsat
  • Abstract:ÌýWhen can isolated many body quantum systems fail to go to equilibrium under their own dynamics, and how robust can this `ergodicity breaking’ be? This question has been a central theme of research in quantum dynamics and statistical mechanics over the past decade, and I will share with you some highlights, focusing on three key developments: many body localization, dynamics with multipolar symmetries, and dynamics with higher form symmetries. I will present the rich and exotic phenomena that arise in these three regimes, and how they may be realized experimentally. I will then discuss some key open directions for the field.

September 11Ìý— "Developing current and next generation physics assessments"

  • Presenter: Bethany Wilcox, ÀÖ²¥´«Ã½, Boulder
  • Host:Tobin Munsat
  • Abstract:ÌýThe ability to measure what students are learning (or not) is a crucial component of crafting effective learning environments. In particular, low-stakes, standardized diagnostic assessments can provide a valuable tool for tracking student learning over time and between instructional approaches to identify effective strategies that improve students' understanding of core physics content. The field of physics education research (PER) has created a number of these assessment instruments targeting content from introductory mechanics up to senior-level thermal physics. While these assessments have provided an important mechanism to ground educational decision making in data on student learning, it is important for these instruments to evolve to meet the needs of a changing educational landscape. In this talk, I will articulate the value of standardized assessments in the context of improving physics programs broadly as well as the need for a new generation of assessment instruments. I will describe work towards meeting these next generation assessment needs for a range of physics content areas.

September 18Ìý— "Mathematics of Nuclear Proliferation"

  • Presenter: Jerry Peterson, ÀÖ²¥´«Ã½ Boulder
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  • Abstract: We are all physicists, and have at least some acquaintance with mathematics.ÌýAnd we all have a fear of nuclear war.ÌýThere are currently nine nations with these dreadful weapons. Can you name them? This colloquium will criticize the current meaning of deterrence, and offer an alternative, with evidence.

September 25Ìý— "Hadron spectroscopy from long ago till the day after tomorrow"

  • Presenter: Tom Degrand, ÀÖ²¥´«Ã½ Boulder
  • Host: Mihaly Horanyi
  • Abstract:ÌýPerhaps "The quark model for an AMO audience'' would be a better title? Anyway, I will tell you a bit about the spectroscopy of strongly interacting particles, a bit about the quark model, a bit about how people calculate the masses of bound states of quarks and gluons, and a bit about some statesÌýthat I think are particularly interesting.

October 2Ìý— "The Dark Energy Spectroscopic Instrument First Year Results: Cosmic Expansion History with Baryon Acoustic Oscillations"

  • Presenter: Julien Guy, Lawrence Berkeley National Laboratory
  • Host: Alysia Marino
  • Abstract:ÌýThe Dark Energy Spectroscopic Instrument (DESI) collaboration is conducting a 5 year redshift survey of 40 million extra-galactic sources over 14,000 square degrees of the northern sky. One of its primary goals is to measure the cosmic expansion history with baryon acoustic oscillations (BAO). I will present the measurement of BAO in galaxy, quasar and Lyman-alpha forest tracers from the first year of observation. With 5.7 million galaxy and quasar redshifts in the range 0.1 < z < 2.1, and 420,000 Lyman-alpha forest quasars at higher redshift, the aggregate precision on BAO is of 0.52% at z<2.1 and 1.1% at an effective redshift z=2.3, surpassing in a year two decades of observations with the SDSS. I will present some of the numerous validation tests performed with simulations and blinded data. I will then highlight the main cosmological results, with improved constraints on the dark energy equation of state, the Hubble parameter, spatial curvature, and the sum of neutrino masses.

October 9Ìý— "Guiding Trojan Beams via Lagrange Points"

  • Presenter: Mercedeh Khajavikhan, University of Southern California
  • Host: Juliet Gopinath
  • Abstract: The guided transmission of optical waves is essential for modern applications in communication, information processing, and energy systems. Traditionally, light guiding in structures like optical fibers has been predominantly achieved through total internal reflection. In periodic structures, a range of other physical mechanisms can also facilitate optical wave transport. However, guiding light in fully dielectric, transversely non-periodic, passive materials remains challenging when total internal reflection is not viable. We introduce an approach to light trapping that leverages the unique properties of Lagrange points—a class of equilibrium positions analogous to those that capture Trojan asteroids in the Sun-Jupiter system. This is accomplished through optical Coriolis forces, which create guiding channels even in regions where the refractive index is defocusing or otherwise featureless. We also explore the potential of extending this mechanism, based on Lagrange points, to guide other wave species, notably charged particle beams in vacuum. As the first waveguide designed for charged particles and enabling transport in the ground state, this approach may open new avenues in particle acceleration, quantum sensing, and quantum computing.
  • Biography: Professor Mercedeh Khajavikhan joined the faculty of the University of ÌýSouthern California in the Ming Hsieh Department of Electrical and Computer Engineering in August 2019 as an Associate Professor and was promoted to a full professor rank in January 2022. She has also a joint appointment at the Department of Physics & Astronomy at USC. She received her Ph.D. in Electrical Engineering from the University of Minnesota in 2009. Subsequently, she joined the University of California in San Diego as a postdoctoral researcher, where she worked on the design and development of nanolasers, plasmonic devices, and silicon photonics components. In August 2012, she started her career as an Assistant Professor in the College of Optics and Photonics (CREOL) at the University of Central Florida (UCF), working primarily on unraveling novel phenomena in active photonic systems. She is the recipient of the NSF Early CAREER Award in 2015, the ONR Young Investigator Award in 2016, the DARPA Young Faculty Award in 2018, the University of central Florida Reach for the Stars Award in 2017, UCF Luminary Award in 2018, and DARPA Director’s Fellowship in 2020. She is a fellow of Optica (formerly known as Optical Society of America OSA) and a fellow of APS (American Physical Society). Her current research interests are in optical thermodynamics, charged particle guiding, novel laser arrays, as well as in topological and non-Hermitian photonics.Ìý

October 16

  • Presenter: Ivan Smalyukh, ÀÖ²¥´«Ã½ Boulder
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October 23Ìý— "How to Predict Space Weather"

  • Presenter: Dan Baker, LASP, ÀÖ²¥´«Ã½ BoulderÌý
  • Host: Mihaly Horanyi
  • Abstract:ÌýThis presentation describes space weather impacts and their economic and societal costs. Modern technological society is characterized by a complex set of interdependencies across its critical infrastructures. These are vulnerable to the effects of intense geomagnetic storms and solar disturbances. Strong currents flowing in the ionosphere can disrupt and damage Earth-based electric power grids and contribute to the accelerated corrosion of oil and gas pipelines. Magnetic storm-driven ionospheric disturbances interfere with high-frequency radio communications and navigation signals from Global Positioning System (GPS) satellites. Exposure of spacecraft to solar particles and radiation belt enhancements can cause operational anomalies, damage critical electronics, degrade solar arrays, and blind optical systems such as imagers and star trackers. Moreover, intense solar particle events present a significant radiation hazard for astronauts during the high-latitude segment of the International Space Station (ISS) orbit as well as for future human explorers of the Moon and Mars. It is imperative that we—as a technological society—develop a truly operational space weather observing and modeling system in which accurate forecasts are effectively provided. In this talk we discuss current space weather prediction capabilities and steps being taken to improve forecasting abilities. We also describe progress being made to reduce the societal impacts from this major natural hazard.

October 30

  • Presenter: Caterina Vernieri, Stanford University, SLAC
  • Host: Alysia Marino and John Cumalat
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November 6

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November 13

  • Presenter: Bruce Remington, Lawrence Livermore National Laboratory
  • Host: Yuan Shi
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November 20

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November 27Ìý—ÌýNo Colloquium, Fall BreakÌý

December 4

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December 11

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