Spring 2026 Colloquium Schedule
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 14 — Joint Physics-APS Colloquium, "String Theory Reborn"
- Presenter: Andrew Hamilton, CU Boulder
- Host: Mike Litos
- Abstract: String theory offers a viable theory of quantum gravity, with spin 2 gravitons encoded in closed strings. But the failure to find evidence for supersymmetry at the LHC has left string theory in an uncertain state. A solution to the problem is in plain sight: revert to classic nonsupersymmetric, bosonic string theory, reenvisaged as a theory of all the forces, not just the strong force. The classic theory correctly reproduces the Brauer-Weyl (1935) algebraic relation between fermions and bosons seen in the standard model, whereas supersymmetry does not.
Sages rejected the classic theory on the grounds that (1) it does not admit fermions, and (2) its ground state is tachyonic. But rejection (1) assumes that fermions are strings, whereas the fermions of bosonic string theory are the endpoints of strings, and are not themselves strings; in modern parlance, the fermions are excitations of the D-brane boundary of strings. As to rejection (2), the properties of the tachyon are precisely those of a Higgs field: it is a multiplet of the unbroken symmetry; the "vacuum" state where the Higgs field vanishes identically is tachyonically unstable; and it has spin zero. The gauge group of bosonic string theory is tightly constrained. I show that a 26-dimensional bosonic string theory that fits the standard model emerges without contrivance. Unburdened by supersymmetry, bosonic string theory has the potential to bring string theory back into the realm of testable physics accessible to present-day observation and experiment.
January 21 — "Quantum Simulation of Correlated Exciton Phases via Ultrafast Optical Microscopy"
- Presenter: Libai Huang, Purdue University
- Host: Markus Raschke
- Abstract: Moiré superlattices formed from transition metal dichalcogenide (TMDC) heterostructures have emerged as a compelling platform for exploring quantum many-body physics. These systems are viewed as a solid-state counterpart to ultracold atomic gases in optical lattices for quantum simulation. A central open question concerns the coherence and dynamics of quantum phases arising from photoexcited moiré excitons, especially under dissipative conditions.
To address this, we employed transient photoluminescence and ultrafast reflectance microscopy to directly image non-equilibrium exciton phase transitions in twisted WS2/WSe2 heterobilayers. Surprisingly, both experimental data and theoretical modeling reveal that strong long-range dipolar repulsion between moiré excitons leads to a freezing of exciton motion in the Mott insulator phase, persisting for over 80 ns. This result defies the conventional expectation that repulsive interactions delocalize particles, while attractive ones promote binding. The observed phenomenon of frozen dynamics due to strong repulsive interactions is characteristic of highly coherent systems, a feature previously realized exclusively in ultracold gases.
We further investigated the interplay between exciton and charge orders in Bose-Fermi mixture, as well as ballistic exciton flow driven by generalized electron Wigner crystals, revealing rich and tunable excitonic correlations in moiré systems.
January 28 — "Adventures in the Ferroelectric Nematic Realm"
- Presenter: Noel Clark, CU Boulder
- Host: Leo Radzihovsky
- Abstract: In 2017-2018 liquid crystal research groups working independently in the UK and Japan, exploring two distinct families of rod-shaped organic molecules, each reported an unknown nematic-like liquid crystal phases in their materials. In 2020 we showed that the unknown phase in the UK compound, RM734, was a ferroelectric nematic: a 3D liquid phase with a fluid spontaneous polarization field, P. This was a notable event in LC science because ferroelectricity was put forth in the 1910’s, by Peter Debye and Max Born, as a possible stabilizing mechanism for the nematic phase. Nematic polar ordering was revisited extensively experimentally since that time, in systems ranging from colloidal suspensions of rods or discs, to main chain polymers, and melts of polar molecules, and claimed but has never established with certainty. Following on we found, in mixtures of RM734 with the Japanese compound DIO, that the unusual phase in DIO was actually the same ferroelectric nematic as in RM734. This convergence moved us to coin the notion “Ferroelectric Nematic Realm,” for what saw for potential as a new soft matter subfield. With two molecules and one phase this wasn’t much of a Realm, but now it has grown to ~500 molecules, making ~15 new phases, and exhibiting a growing body of exotic LC phenomenology. I will present some of the highlights of the chemical physics and applications of this fundamentally new kind of fluid.
February 4 — "Nowcasting Extreme Event Risks"
- Presenter: Andrew Gettelman, Pacific Northwest National Laboratory, University of Colorado, Boulder
- Host: Ivy Tan
- Abstract: Earth’s climate is changing quickly enough that relying on historical weather statistics to estimate the risk of extreme events is no longer reliable. Communities, infrastructure planners, and policymakers increasingly need information about how the likelihood of extreme weather may change over the next 10–15 years in order to plan and adapt. However, existing tools do not adequately address this need. Weather forecasts focus on timescales of days to weeks, while climate projections are typically aimed decades into the future. Even initialized decadal climate predictions face major scientific and practical challenges and are unlikely to fully bridge this gap.
In this talk, I will argue for a different approach: climate nowcasting. Climate nowcasting aims to estimate near-term climate risk by combining observations, physical climate models, and data-driven methods to better characterize the current state of the climate system and how it is likely to evolve over the coming decade. Rather than focusing on global averages, this approach emphasizes specific regions, types of extreme events, and risks at human-relevant spatial scales of a few kilometers.
Beyond its practical value, a climate nowcasting framework also offers a new way to study predictability in the Earth system. By focusing on conditional risk—how future extremes depend on the present climate state—it may help improve our understanding of what aspects of climate are predictable on decadal timescales and how to better quantify uncertainty in a rapidly changing system. The presentation will be illustrated with examples of typical (and topical) weather extremes relevant to Boulder: extreme wind, fire weather and variability in seasonal snowpack.
February 11 — "Quantum synchronization: harnessing noise to create coherence"
- Presenter: Eric Bittner, University of Houston
- Host: Sean Shaheen
- Abstract: Synchronization—the spontaneous emergence of phase coherence among interacting oscillators—is a ubiquitous phenomenon in classical systems, from pendulum clocks to biological rhythms. In quantum systems, however, coherence is fragile, and environmental noise is usually viewed as its primary adversary. This colloquium explores a counterintuitive regime in which noise itself becomes a resource, driving rather than destroying coherent behavior. I will discuss how correlated dissipation and structured environments can induce synchronization between quantum degrees of freedom that do not synchronize in isolation. Using simple but physically motivated models—ranging from coupled qubits and oscillators to excitonic and polaritonic systems—I will show how environmental correlations reshape the system’s dynamical symmetry, protect specific collective modes, and lead to robust phase locking even in the presence of strong decoherence. A central theme will be the role of symmetry and mode structure: by transforming to collective coordinates, one finds that noise correlations can selectively suppress dissipation in certain subspaces while enhancing it in others, effectively stabilizing synchronized quantum motion. I will also discuss how these effects manifest in experimentally accessible observables, including coherence measures, spectral responses, and photon correlations, and how they connect to recent ideas from open quantum systems, exceptional points, and quantum information theory. Beyond its conceptual interest, noise-induced quantum synchronization offers a new route to controlling coherence in realistic, dissipative platforms, with implications for quantum sensing, molecular photonics, and engineered quantum materials.
February 18 — "Cosmic mineralogy: from diamonds to quasicrystals"
- Presenter: Terry Wallace, Lawrence Livermore National Laboratory
- Host: Markus Raschke
- Abstract: The mineralogy of our planet is a fingerprint of history—a durable archive of the physical and chemical conditions that have evolved over 4.5 billion years. Minerals record temperatures and pressures, redox states and fluid compositions, preserving evidence that spans the earliest violent collisions of solar-system formation to human activities that occurred only yesterday. Yet Earth’s mineral story reaches far deeper in time, extending back to the very origins of the elements themselves.
This talk traces mineral evolution from the formation of the most rudimentary elements in the first few hundred thousand years after the Big Bang, through the birth of the first stars and the onset of stellar nucleosynthesis, to the creation of the heaviest elements in kilonova explosions. These elements were dispersed into interstellar gas clouds, recycled through multiple generations of stars, and ultimately assembled into planets. The first minerals to form in the universe—diamond and graphite—were forged under extreme conditions and endlessly recycled, providing the elemental backbone for life. Today, roughly 6,000 mineral species are known on Earth; each one offers a distinct window into our cosmic history.
February 25 — "Transcendental conditions for the successful use of effective field theories"
- Presenter: Adam Koberinski, Rotman Institute of Philosophy, Western University
- Host: Heather Demarest
- Abstract: Effective field theories (EFTs) form the basis of our most successful theories of matter, both in particle physics and in condensed matter physics. But the structure of EFTs poses a challenge to many standard philosophical accounts of theory structure and content. In particular, the inability to cast EFTs in terms of exact mathematical objects defined at all scales suggests that philosophical accounts of theory interpretation ought to be modified to deal with approximate, scale-relative ontologies. In this talk, I take some preliminary steps toward an alternative approach to theory interpretation, suitable to EFTs as well as other mathematized theories. Starting from the assumption that EFTs currently allow us to successfully learn about the world, I explicate some features the world must have for that to be true.
March 4 — "Atmospheric particle physics from CERN to Boulder to the Southern Ocean"
- Presenter: Hamish Gordon, Carnegie Mellon University
- Host: Ivy Tan
- Abstract: Low energy collisions between molecules in the atmosphere lead to about 50% of the particles that act as the seeds for cloud droplets. Many of these molecules, and many of the other particles, are the result of human activity. Therefore cloud droplet concentrations have increased over the industrial period. The increase has led to a poorly quantified cooling effect on Earth that has offset perhaps a third of historical warming from greenhouse gases. The CLOUD experiment at CERN is a laboratory facility for the study of atmospheric particle formation. In my talk I will show how we are using results from this facility to represent this process better in climate models. As particle formation in the atmosphere is strongly dependent on meteorology, it is also critical to study how it happens in situ and to test our models with real observations. I will show how we are characterizing the process using aircraft measurements, in areas including the Front Range and the remote Southern Ocean.
- Bio: Hamish Gordon is an associate professor in the Department of Chemical Engineering and the Center for Atmospheric Particle Studies at Carnegie Mellon University. His research interests are focused on the effects of air pollution and natural airborne particles on clouds and climate. He received his first degree from the University of Cambridge in 2009, and his doctorate from the University of Oxford in experimental high energy physics in 2013. After postdoctoral positions first at CERN and then at the University of Leeds, he moved to Carnegie Mellon in 2019. In 2025 he was awarded an NSF CAREER grant for a proposal titled "Role of new particle formation in pre-industrial climate" and served as a forecaster and mission scientist for the HALO-South aircraft campaign from Christchurch, New Zealand.
March 11 — "An Experimental Quantum-Optical Spin Glass: From Ultrametricity to Associative Memory"
- Presenter: Ben Lev, Stanford University
- Host: Ana Maria Rey
- Abstract: Spin glasses are canonical examples of complex matter and form a basis for describing artificial neural networks. Repeatable control over microscopic degrees of freedom might open a new window into their structure and dynamics. I will present how we achieved this at the atomic level using a quantum-optical system comprised of ultracold gases of atoms coupled via photons resonating within multimode cavities. The controllability provided by this new spin glass system has allowed us to directly measure spin dynamics and replica symmetry breaking, yielding the first direct observation of ultrametricity in a physical system. We use this spin glass to realize an associative memory with a capacity exceeding that of the Hopfield model.
No Colloquium March 18 — Spring Break
March 25
- Presenter: Mehran Kardar, Massachusetts Institute of Technology
- Host: Leo Radzihovsky
- Abstract:
April 1
- Presenter: Scott Pratt, Michigan State University
- Host: Jamie Nagle
- Abstract:
April 8
- Presenter: Rachel Henderson, Michigan State University
- Host: Bethany Wilcox
- Abstract:
April 15
- Presenter: Phil Nelson, University of Pennsylvania
- Host: Leo Radzihovsky
- Abstract:
April 22
- Presenter: Long Ju, Massachusetts Institute of Technology
- Host: Victor Gurarie
- Abstract:
For more information about colloquia this semester, contact: Mike Litos