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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.

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

• Presenter: Chuankun Zhang, JILA
• Host: Jun Ye
• Abstract: Laser-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 4 — "Ergodicity breaking in quantum dynamics"

• Presenter: Rahul Nandkishore, University of babyֱ��app Boulder
• Host:Tobin Munsat
• Abstract: When 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 11 — "Developing current and next generation physics assessments"

• Presenter: Bethany Wilcox, University of babyֱ��app, Boulder
• Host:Tobin Munsat
• Abstract: The 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 18 — "Mathematics of Nuclear Proliferation"

• Presenter: Jerry Peterson, University of babyֱ��app Boulder
• Host: 
• Abstract: We are all physicists, and have at least some acquaintance with mathematics. And we all have a fear of nuclear war. There 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 25 — "Hadron spectroscopy from long ago till the day after tomorrow"

• Presenter: Tom Degrand, University of babyֱ��app Boulder
• Host: Mihaly Horanyi
• Abstract: Perhaps "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 states that I think are particularly interesting.

October 2 — "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: The 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 9 — "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 babyֱ��app of the University of  Southern 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. 

October 16 — "Metaatoms and metamaterials for fun and to save the world"

• Presenter: Ivan Smalyukh, University of babyֱ��app Boulder
• Host: Mihaly Horanyi
• Abstract: Words of Richard Feynman “What I cannot create, I do not understand” inspire researchers to develop artificial building blocks of matter. This pursuit has the potential to boost our understanding of nature’s inner workings by re-creating phenomena and testing theories from research fields like cosmology in experimentally accessible physical systems like liquid crystals, colloids and magnets. It also allows for making new types of materials by design, allowing for physical properties not encountered in nature. 
  In my talk, I will discuss how vortex knots in liquid crystals can exhibit atom-like behavior, including fusion, fission and self-assembly into various crystals with giant electrostriction properties. These findings will  let us admire the beautiful history of the early model of atoms by Lord Kelvin, as well as the very last poem by Maxwell related to it. I will then show that these vortices interact with light similar to what was predicted for the elusive cosmic strings, with knots and arrays of vortices allowing for spatially localizing beams of light into closed loops and knots for technological uses. Finally, I will discuss how we also develop mesostructured metamaterials that combine thermal super-insulation with pre-designed light transmission in visible and infrared spectral ranges to re-create Earth's greenhouse effect on much smaller scales, which can be useful for harvesting solar energy, boosting efficiency of buildings and potentially even allowing for extraterrestrial habitats. 

October 23 — "How to Predict Space Weather"

• Presenter: Dan Baker, LASP, University of babyֱ��app Boulder 
• Host: Mihaly Horanyi
• Abstract: This presentation describes space weather impacts and their babyֱ��app 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 — "Delving into the Unknown: The Higgs Boson at Future Colliders"

• Presenter: Caterina Vernieri, Stanford University, SLAC
• Host: Alysia Marino and John Cumalat
• Abstract: The Higgs boson was discovered in 2012 by the ATLAS and CMS experiments at the world’s most powerful particle collider, the Large Hadron Collider (LHC) in Geneva, Switzerland. This particle plays a unique role in fundamental physics. It gives all of the known elementary particles, including itself, their masses. While we now have a strong evidence that the Higgs field is indeed the unique source of mass for the known elementary particles, the next step is to search for new interactions that could also explain why the Higgs field has the properties required by the Standard Model of particle physics. We have no clear roadmap to this new theory but the Higgs boson plays a crucial role in this quest. The goal of a next-generation e+e- collider is to carry out precision measurements to per-cent level of the Higgs boson properties that are not accessible at the LHC. In this talk we present the challenges and possibilities for the next e+e- collider and recent progress. The exploitation of the complementarity between LHC and future colliders will be the key to understanding fundamentally the Higgs boson.

November 6 — "Plasma-based Accelerators for Ultra High Energy Colliders"

• Presenter: Spencer Gessner, Stanford University, SLAC
• Host: Michael Litos
• Abstract: Recent experiments at SLAC demonstrated beam-driven plasma acceleration with accelerating gradients in excess of 150 GeV/m. That’s nearly 10,000 times the accelerating gradient produced by RF cavities in the SLAC linac! Plasma accelerators are a promising technology for future ultra-high energy colliders and were identified by the P5 Panel as a path toward 10 TeV collisions. In this talk, I’ll review the physics of nonlinear plasma wakefield acceleration. What makes the plasma bubble nearly-ideal for electron acceleration? Why does it fail for positron acceleration? I’ll conclude by describing the US 10 TeV Wakefield Collider Design Study and the next steps in plasma accelerator R&D.

November 13 — "New regimes of frontier science on the NIF laser and supporting HED facilities"

• Presenter: Bruce Remington, National Ignition Facility Discovery Science Program Leader, Lawrence Livermore National Laboratory
• Host: Yuan Shi
• Abstract: Highlights from research done on the National Ignition Facility (NIF) laser through the Discovery Science program will be presented. Plasma nuclear reactions relevant to stellar nucleosynthesis and nuclear reactions in high energy astrophysical scenarios are being studied. [1] Equations of state (EOS) at very high pressures (0.1-100 TPa or 1-1000 Mbar) relevant to planetary cores, brown dwarf interiors, and white dwarf envelopes are being measured on NIF, and show that the level of ionization can significantly affect the compressibility of the sample. [2-6] Studies of Rayleigh-Taylor instabilities in planar and cylindrical geometries at high Reynolds number, relevant to supernovae explosions and ICF implosions, are being investigated. [7-12] Relativistically hot plasmas [13,14] and target-normal sheath acceleration (TNSA) of protons [15-17] are also being studied on the NIF ARC laser. Experiments to study magnetic reconnection at high energy densities are underway. [18] High velocity, low density interpenetrating plasmas that generate collisionless astrophysical shocks, magnetic fields, bursts of neutrons, and that accelerate particles relevant to cosmic ray generation are also being studied on NIF. [19-21] And NIF experiments have demonstrated strong suppression of heat conduction in a laboratory replica of galaxy-cluster turbulent plasmas. [22] A selection from these results will be presented and a path forward suggested.
  References:
  [1] M. Gatu Johnson, PoP 24, 041407 (2017); and PoP 25, 056303 (2018).
  [2] T. Döppner, PRL 121, 025001 (2018).
  [3] A.L. Kritcher, Nature 584, 51 (2020).
  [4] A. Lazicki, Nature 589, 532 (2021).
  [5] R.F. Smith, Nature 511, 330 (2014).
  [6] R.F. Smith, Nature Astron. 2, 452 (2018).
  [7] C.C. Kuranz, Nature Commun. 9, 1564 (2018).
  [8] J.P. Sauppe, PRL 124, 185003 (2020).
  [9] S. Palaniyappan, PoP 27, 047208 (2020).
  [10] A. Casner, PoP 22, 056302 (2015).
  [11] A. Casner, PPCF 60, 014012 (2018).
  [12] D.A. Martinez, PRL 114, 215004 (2015).
  [13] G.J. Williams, PRE 101, 031201 (2020).
  [14] G.J. Williams, PRE 103, L031201 (2021).
  [15] D. Mariscal, PoP 26, 043110 (2019).
  [16] R.A. Simpson, PoP 28, 013108 (2021).
  [17] N. Iwata, PRR 3, 023193 (2021).
  [18] V. Valenzuela-Villaseca, PoP 31, 082106 (2024).
  [19] Steve Ross, PRL 118, 185003 (2017).
  [20] F. Fiuza, Nature Physics 16, 916 (2020).
  [21] D.P. Higginson, PoP 26, 012113 (2019).
  [22] J. Meinecke, Sci. Advances 8, eabj6799 (2022).

November 20 — "Improving the Performance of  Superconducting Qubits"

• Presenter: Corey Rae McRae, University of babyֱ��app, Boulder
• Host:
• Abstract: Superconducting quantum computers, once scaled up, could solve problems intractable to even the largest classical supercomputers, but better superconducting qubits are needed before this can occur. Superconducting qubit coherence is currently limited both by cryogenic low-power dielectric loss and by large temporal fluctuations due to strongly-coupled defects. In this talk, I discuss how single qubit performance is generally understood, models and proposed sources of decoherence, and new research disentangling decoherence channels in superconducting circuits, all of which is needed to build better, more scalable superconducting qubits. 

November 27 — No Colloquium, Fall Break 

**CANCELLED** December 4 — "The Future of High-Energy Colliders: Challenges and Opportunities with Muons"

• Presenter: Isobel R. Ojalvo, Princeton University
• Host: Alysia Marino
• Abstract: By pushing the bounds of the energy frontier, physicists have uncovered the fundamental particles and interactions that are responsible for our visible universe. But this work is not done: Dark Matter remains a mystery, and while the Higgs boson has been discovered, we have no understanding yet of its origin or the role it may have played in the birth of the Universe.  To explore the energy frontier, we have built larger and larger colliders utilizing the two charged particles that are easiest to produce and manipulate, the proton and the electron. As we push forward towards the future of high-energy colliders, using these particles have fundamental problems: the electron due to synchrotron radiation and the proton due to its composite nature. A compact and power-efficient collider using muons (heavy partners of the electron) would represent a paradigm shift in particle physics; it would allow physicists to explore an entirely new energy regime. In this talk, I’ll discuss the challenges and possibilities of a muon collider and give an overview of recent progress toward making one a reality.

December 11 — "Life on an Endless Hill: Making Sense of Up-Side-Down
Potentials in Quantum Mechanics and High Energy Physics"

• Presenter: Paul Romatschke, University of babyֱ��app, Boulder
• Host: Tobin Munsat
• Abstract: In classical physics, unbounded (or "up-side-down") potentials do not allow for a stable ground state. As a consequence, unbounded potentials have often been dismissed as not viable for proper unitary quantum theories. Historically, we have learned that the quantum world often contradicts dearly held beliefs based on classical physics. By contrast, mathematics has been recognized as a good guide even when classical intuition fails.  In this talk, I will use well-developed mathematics to explore physical systems with up-side-down and non-Hermitian potentials in quantum mechanics and quantum field theory, with applications to AMO experiments, high energy physics and Quantum Chromodynamics.

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