Abstract: Achieving ballistic, coherent charge and energy flow in materials at room temperature is a long-standing goal that could unlock ultrafast, lossless energy and information technologies. The key obstacle to overcome is short-range scattering between electronic particles and lattice vibrations (phonons). I will describe two promising avenues for realizing ballistic transport in two-dimensional (2D) semiconductors by harnessing hybridization between electronic particles and long-wavelength excitations. First, I will show that beyond-perturbative interactions between electrons and delocalized phonons in flat-band materials can result in the formation of 2D acoustic polarons. These polarons are protected from scattering, resulting in sustained ballistic transport over macroscopic spatiotemporal scales at room temperature, a remarkable phenomenon we are beginning to harness in electronic devices. I will then focus on hybridization between semiconductor excitons and light to form polaritons, demonstrating that these hybrid quasiparticles display long-range ballistic transport at light-like speeds even in the presence of finite interactions with lattice phonons. I will conclude with new prospects for leveraging polaritons to control material function even in the absence of illumination. In all cases, we develop ultrafast optical imaging capabilities enabling us to track the propagation of these quasiparticles with femtosecond resolution and few-nanometer sensitivity, providing precise measurements of transport dynamics and sensitivity to both static and dynamic disorder.

We live in a world where everything spins! Join CU Wizards on an exciting adventure to discover what that means, how it feels, and why things get weird when they spin! 

Gwen Eccles, CU Physics Demonstration Coordinator, presents the first show of the CU Wizards season that will include hands-on activities for the audience.

For over 40 years, CU Wizards has been delighting families at CU Boulder with engaging, FREE STEM Saturday morning shows. These spectacular monthly events have introduced thousands of PK-12 students and their families to the wonders of the natural world. All are invited to attend. Don’t miss out on this fantastic opportunity for educational fun! 

For more information, visit: www.colorado.edu/cuwizards.

Solar flares and coronal mass ejections (CMEs) are powered by the sudden release of magnetic energy stored in the Sun’s low corona as a result of magnetic reconnection. Understanding these explosive events requires tracking how magnetic fields evolve—not only during, but also before the eruptions. Yet direct measurements of the 3D coronal magnetic field remain a major challenge. In this talk, I will overview what we currently know about the structure of the pre-eruption magnetic field and the physical mechanisms that trigger eruptions. I will also present recent results from both statistical and case-study analyses of Solar Dynamics Observatory and DKIST observations as well as data-driven MHD simulations of eruptive flares. I will conclude by looking ahead to the exciting future of solar physics, as new observatories will provide key empirical constraints on the physics of the solar flares in the decade to come.

Please join us for the first Life After JILA Seminar of the semester on Monday, September 15th! Aaron Leanhardt, a former JILA postdoc from the Cornell group, will be speaking about his journey from JILA to professorship to coaching Major League Baseball for the Miami Marlins. 

There will be a reception at the Sink at 5:30 pm after the talk, where students and postdocs can talk to Aaron more about his career. The seminar and the meetup are open to everyone, so please invite your friends! There will be refreshments during the talk and appetizers at the meetup at the Sink. After the talk, we will meet on the first floor of the JILA tower at 5:15 pm so we can walk over to the Sink together. 

Life after JILA is a seminar series that brings back JILA alumni to talk to current graduate students and postdocs about their careers after leaving CU. Our goal is to showcase diverse career paths and introduce students to options outside of the "traditional" academic environment. Students, postdocs, staff, and professors are all welcome to attend, regardless of department or affiliation. Please see below for more details about the talk. 

Please contact Anya Grafov (Anya.Grafov@colorado.edu) for any questions about the event. 

Speaker: Aaron Leanhardt

Date/Time: Monday, September 15^th at 4:00 pm

Location: JILA X317/325

Speaker bio: 

Life *Before* JILA -- I was an undergraduate student at the University of Michigan where I majored in Electrical Engineering and worked in a physics lab studying the lifetime of Positronium atoms.  I moved on to graduate school at MIT where I earned a PhD in Physics working on "Microtraps and Waveguides for Bose-Einstein Condensates". 
Life *At* JILA -- I was a post-doctoral scholar on the upstart HfF+ electron EDM experiment, which has subsequently gone on to set new limits for violations of the Standard Model.  

Life *After* JILA -- well, that's a work-in-progress and the subject of this presentation!  Somehow I have managed to transition from running a windowless lab in the sub-basement of the physics building as an Assistant Professor at the University of Michigan to baking under the summer sun in the dugout of MLB games as the Major League Field Coordinator for the Miami Marlins.

Due to their strong, long-range, and tunable dipolar interactions, ultracold polar molecules can realize spin-motion models with rich many-body physics. Using a spin encoded in rotational states of fermionic KRb molecules, we demonstrate tuning of Heisenberg XXZ models with electric fields and Floquet engineering of XYZ models with microwave pulse sequences. By controlling motion with optical lattices, we explore highly tunable generalized t-J models. Observing new dynamics and phases predicted for these models also requires low-entropy initial states. We report progress toward producing a deeply degenerate Fermi gas in an isolated 2D layer using a tunable-spacing optical lattice.

Host: Dylan Taatjes

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Host: Mihaly Horanyi

Abstract: While the properties of soft materials are ultimately dictated by their electronic structure, exploiting this knowledge for the design of non-crystalline materials has long been a formidable computational challenge. I will define conceptual and practical barriers that limit quantum mechanical design in soft materials and discuss recent work aimed at removing these barriers. First, I will describe the development of electronic structure models that leverage AI to operate at coarse-grained resolutions, enabling electronic design in non-crystalline molecular solids and polymers. Second, I will discuss how AI-driven strategies, tightly coupled with experimentation, can tackle soft materials reactivity challenges outside of the purview of traditional theoretical and computational methods. These developments chart a path towards predictive soft materials engineering grounded in electronic structure and chemical reactivity.

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Host: Ana Maria Rey

Abstract: Proteins operate within an aqueous environment that influences their folding, stability, and activity. Membrane proteins have the added complication of being embedded in lipid bilayers that play an equally critical, yet significantly less understood, role. Much like solvent conditions modulate enzyme kinetics and protein interactions in solution, the lipid composition of the membrane performs regulatory functions for membrane proteins, affecting their organization, conformational dynamics, and catalytic output. To investigate these membrane-dependent phenomena, we employ time-resolved fluorescence spectroscopy techniques like pulsed interleaved excitation fluorescence cross-correlation spectroscopy (PIE-FCCS) in model membranes and live cells. We couple these spectroscopic probes with liposome-based activity assays in vitro. These complementary approaches allow us to quantitatively assess how specific lipid species influence the assembly and function of receptor tyrosine kinases (RTKs).

In this talk, I will highlight two key areas where lipid–protein interactions govern RTK behavior. First, I will describe how the anionic lipid phosphatidylinositol 4,5-bisphosphate (PIP₂) promotes multimeric assembly of EGFR and EphA2 in the plasma membrane, driving the formation of functionally distinct signaling complexes, as revealed by PIE-FCCS in live cells. Second, I will present our recent in vitro findings showing that both PIP₂ and phosphatidylserine (PS) act as reversible, noncompetitive inhibitors of EGFR catalytic activity in a reconstituted liposome system, demonstrating direct biochemical regulation of kinase function by anionic lipids. Together, these results reveal that the lipid bilayer is not merely a scaffold but an active participant in membrane protein regulation. By drawing parallels to the well-established influence of solvent on soluble proteins, we hope to center the membrane environment as a dynamic and tunable component of cell signaling.

The availability of exascale computing resources has enabled numerical modeling of astrophysical fluid dynamics at unprecedented scale, including studies of MHD turbulence on grids with 10,000^{3} cells, or MHD models of black hole accretion in full GR with radiation transport. Results from a diverse range of applications will be presented, including new insights into the structure of radiation-dominated accretion disks, modeling AGN feedback in elliptical galaxies, and turbulence and cosmic ray transport in the interstellar medium.

Abstract: Social bonds live in our biology. To understand the computations that allow our brains to form social bonds, my lab studies monogamous prairie voles. Unlike laboratory mice and rats, these rodents often mate for life, parenting together and defending a shared home. We have found that social information is organized at multiple scales in the brain's reward center—from stable encoding in individual neurons to coordinated ensembles—to enable bond formation. Once these bonds are formed, they lead to an alignment of brainscapes between partners, evident in patterns of neural activity and molecular alignment. Ultimately, this work delineates how social relationships change the brain beginning with their initial encoding mechanisms and then establishing a framework that facilitates connectedness and may help pairs effectively navigate the world together.

Abstract: My talk will highlight new directions in probing semiconductor electrochemistry and reactivity at the single-particle and single-molecule level. I will discuss our recent discovery that the band gap renormalization (BGR) effect in 2D semiconductors strongly dictates their current–voltage behaviorin electrochemical cells, providing a new framework to understand solid-state transistor device performance variability. I will then describe how single-particle photoelectrochemistry of BiVO₄ reveals unexpected facet-dependent heterogeneity that links structural defects and surface terminations to reactivity. Finally, I will present super-resolution imaging results of surface defect states in semiconductor nanocrystals, where direct visualization opens new possibilities for correlating local electronic structure with photophysical function. Together, these studies illustrate how multi-scale imaging and spectroscopy can unravel fundamental mechanisms of charge generation, separation, and storage in semiconductor materials for energy conversion.

Abstract: Polaritons are hybrid light-matter states with unusual properties that arise from strong interactions between a molecular ensemble and the confined electromagnetic field of an optical cavity. Cavity-coupled molecules appear to demonstrate energetics, reactivity, and photophysics distinct from their free-space counterparts, but the mechanisms and scope of these phenomena remain open questions. I will discuss new experimental platforms that the Weichman Lab is developing to investigate molecular reaction dynamics under strong cavity coupling.

While polaritons are now well-established in solution-phase and solid-state systems, they had not been previously reported in isolated gas-phase molecules, where attaining sufficiently strong light-matter interactions is a challenge. We access the strong coupling regime in an intracavity cryogenic buffer gas cell optimized for the preparation of simultaneously cold and dense ensembles and report a proof-of-principle demonstration in gas-phase methane. We strongly cavity-couple individual rovibrational transitions and probe a range of coupling strengths and detunings. In ongoing work, we are harnessing this infrastructure as a testbed for fundamental studies of polariton physics and chemistry.

We are also searching for signatures of cavity-altered dynamics in benchmark solution-phase systems. So far, we have focused on radical hydrogen-abstraction processes, which have well-characterized reactive surfaces and can be initiated with photolysis and tracked directly on ultrafast timescales. We use ultrafast transient absorption to examine intracavity reaction rates with the goal of better understanding exactly how and when reactive trajectories may be influenced by strong light-matter interactions.

The Department of Physics at the University of Colorado Boulder in collaboration with CUbit and JILA is hosting the third annual Physics and Quantum Career & Internship Fair on Friday, October 17^th from 12:00 - 3:00 p.m. in the Glenn Miller Ballroom.

This event will feature employers across all areas of theoretical, experimental, and computational physics. The fair will connect physics undergraduate and graduate students and recent alumni with laboratory and industry leaders to learn about internships and employment opportunities.

Sign up online

Handshake is CU's online recruiting tool used by thousands of employers. It is recommended, but not required for students to sign up for the 2025 Physics and Quantum Career Fair on Handshake.

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Full Technical Registration Required
JILA is one of the nation’s leading research institutes in the physical sciences. Located at the base of the Rocky Mountains on the University of Colorado Boulder campus, JILA was founded in 1962 as a joint institute of CU Boulder and the National Institute of Standards and Technology. JILA’s scientists explore some of today's most challenging and fundamental scientific questions about the limits of quantum measurements and technologies, the design of precision optical and X-ray lasers, the fundamental principles underlying the interaction of light and matter, the role of quantum physics in chemistry and biology, and the processes that have governed the evolution of the Universe for nearly 14 billion years. JILA’s history is marked by many scientific breakthroughs, including the first demonstrations of a frequency comb and a Bose-Einstein condensate. During your visit to JILA, you will have the opportunity to tour research laboratories and the world-renowned JILA Instrument Shop, followed by a walk through the beautiful campus of CU Boulder to a delicious campus dining hall (the C4C), which can accommodate most common food allergies.

Tour Itinerary

09:00: Depart from Denver (Location to be Determined)

10:00: Arrive at University of Colorado Boulder

10:00 - 12:30: JILA Lab Tours

12:30 - 13:30: Break for Lunch

13:30: Ride back To Denver

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