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Colloquia are held on Thursdays at 4pm in room 4327 (building 4) of the Stevenson Science Center unless otherwise noted. Click here for directions, or phone the department. A reception with the speaker is held at 3:30pm in Stevenson 6333.

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Fall 2019

Thursday August 29th 2019 4:00 PM

Carlos Silva, Georgia Institute of Technology

Exciton polarons in two-dimensional organic-inorganic hybrid perovskites   (show abstract)

While polarons — charges bound to a lattice deformation induced by strong electron-phonon coupling — are understood to be primary photoexcitations at room temperature in three-dimensional hybrid organic-inorganic perovskite (HOIP) lattices, excitons are the stable quasiparticles in two-dimensional (2D) HOIPs. In this colloquium, I will address the question: are polaronic effects consequential in the exciton properties of these materials? Establishing the role of exciton polarons is a key fundamental issue for the rigorous description of the materials physics of 2D HOIPs. Based on our recent work, I will argue that exciton-polaron effects are manifested in the generally observed spectral fine structure comprised of four distinct, non-degenerate exciton resonances with constant inter-peak energy spacing that varies weakly upon substitution of organic cation. I will discuss the possible role of polaronic effects in establishing the finestructure along with alternative interpretations presented in the literature, including the effects of vibronic structure, Rashba splitting, and exchange interactions. Finally, I will address the consequences of polaronic effects on the quantum dynamics of these materials, relevant for applications in optoelectronics, such as light-emitting diodes, lasers, and polariton spontaneous coherence.

Host:R. Haglund

Thursday September 5th 2019 4:00 PM


Thursday September 12th 2019 4:00 PM

Scott Gaudi, Ohio State University

The Demographics of Exoplanets with WFIRST   (show abstract)

Measurements of the demographics of exoplanets over a range of planet and host star properties provide fundamental empirical constraints on theories of planet formation and evolution. I will discuss various efforts to measure and synthesize exoplanet demographics over broad regions of parameter space. Because of its unique sensitivity to low mass, long period, and free floating planets, microlensing is an essential complement to our arsenal of planet detection methods. I motivate, and provide expectations for, a microlensing survey with WFIRST, which when combined with the results from Kepler, will yield a nearly complete picture of the demographics of planetary systems throughout the Galaxy

Host:R. Scherrer

Thursday September 19th 2019 4:00 PM


Gerald Gabrielse, Trustees Professor and Director of the Center for Fundamental Physics at Northwestern University

Tabletop Searches for New Physics: a Tale of Two Electron Dipole Moments    (show abstract)

The fundamental mathematical description of physical reality, the Standard Model of Particle Physics, is the great triumph and the great frustration of modern physics. The great triumph is that all laboratory measurements are so far consistent with its predictions. The great frustration is that the Standard Model is clearly wrong, or at least significantly incomplete, in that it cannot account for many basic features of our universe. Measurements of the magnetic and electric dipole moments of the electron are crucial tests of the Standard Model. The measured magnetic dipole moment of the electron, the most accurately determined property of an elementary particle, is a test of the Standard Model's most precise prediction. The measured electric dipole moment of the electron tests the relative validity of the dramatically predictions of the Standard Model and of proposed improvements (e.g. supersymmetric models) This work was supported by the USA NSF.

Host:N. Tolk

Monday September 23rd 2019 4:00 PM

David Brin, Astrophysicist and Novelist

Our place in the Cosmos and Is Anyone Out There   (show abstract)

In both science and literature, the question of ‘others’ can be a mirror illuminating our own origins and plausible destinies. Are we a fluke? Might we be the first to navigate the minefield of existence? Astrophysicist and novelist David Brin will (briefly) survey both what we know and can speculate about life in the universe.

Host:R. Scherrer

Thursday September 26th 2019 4:00 PM

Les Johnson, NASA

Perspectives at 50: Space Science and Exploration Past, Present, and Future   (show abstract)

After the Apollo astronauts landed on the moon, the Space Race ended. The achievements in human space flight continued with the successes of Skylab, the Space Shuttle, and the International Space Station. With the retirement of the Space Shuttle fleet in 2011, America has been relying on Russia to carry its crews into space. Today, we are in the midst of a new Race to Space, with various commercial companies vying to claim the mantle of returning Americans to space in American-made rockets – providing revolutionary changes in the economics of space travel. A similar revolution in cost and capability is occurring in the robotic science community, allowing small businesses, universities, and non-profit research institutions to build and fly small spacecraft with capabilities rivaling those previously in the exclusive domain of governments. Today, for the first time since the 1960’s, there is a sense of unbounded optimism regarding the human future in space and our ability to send our robotic emissaries to the outer reaches of the solar system and beyond.

Host:N. Tolk

Thursday October 3rd 2019 4:00 PM


Thursday October 10th 2019 4:00 PM

Julie Hogan, Bethel University

CMS Particle Flow: the LEGO tutorial and searches for new massive quarks   (show abstract)

The Compact Muon Solenoid detector at CERN's Large Hadron Collider uses a method called "particle flow" to interpret electronic signals in detector elements as particles like electrons or muons. This critical software is rarely learned in detail by young CMS researchers. I will share an engaging new hands-on tool developed for summer tutorials at Fermilab: the Particle Flow LEGO Experience. Then I will present recent searches for new physics particles called "vector-like quarks", which decay to a variety of massive quarks and bosons. In these searches we connect the particle flow information from showers of quark-based particles with machine learning algorithms to probe for evidence of new physics.

Host:S. Starko and R. Scherrer

Thursday October 17th 2019 4:00 PM


Calen Henderson, IPAC-Caltech

Exoplanet Demographics from Kepler to WFIRST   (show abstract)

Over the past decade we have witnessed an acceleration in the pace of exoplanet detection and characterization. In particular, the Kepler space telescope facilitated the first large-scale studies of planet demographics, illuminating trends as a function of both planet radius and orbital period. The nature of the mission, however, led to these results being focused on planetary systems nearby to the Sun and to planets orbiting close-in to their host star. Yet more recently, gravitational microlensing has made myriad advancements with regard to characterizing individual planetary systems and exploring relatively unknown demographic regimes for planets orbiting at larger distances from their host stars, and located farther from the Solar neighborhood, including for free-floating planets not gravitationally tethered to any host star. I will highlight a handful of results, placing them in the context of what we have learned from Kepler. Then I will discuss the anticipated findings from WFIRST, NASA’s next flagship astrophysics mission, which will conduct a large-scale exoplanetary microlensing survey toward the center of the Milky Way.

Host:S. Jacklin

Thursday October 31st 2019 4:00 PM

Shriram Ramanathan, Purdue University

Quantum materials for brain and biological sciences   (show abstract)

The survival instinct is ubiquitous across organisms. Intelligence and cognitive capability however are correlated with the complexity of the nervous system, e.g. neuronal diversity and is enhanced by transfer of evolutionary knowledge and lifelong learning. We will consider examples where such organismic behavior can be realized in programmable quantum materials. Using the metastable perovskite nickelates as a model system, we will discuss insulator-metal transitions that are controlled by hydrogen doping highlighting recent discoveries on electronic structure modulation approaching the predictions of Verwey and Mott. From understanding the binding of the charge carriers to the lattice, we will describe two experiments in nickelates that mimic classic observations in biology, namely habituation in the sea slug Aplysia and ancestral intelligence in sharks. We will conclude with suggestions for future research to design AI machines that can exploit strong Coulomb interactions in ionic lattices.

Host:R. Haglund

Thursday November 7th 2019 4:00 PM

Prem Kumar, Northwestern University

Quantum Engineering: A Transdisciplinary Vision   (show abstract)

A global quantum revolution is currently underway based on the recognition that the subtler aspects of quantum physics known as superposition (wave-like aspect), measurement (particle-like aspect), and entanglement (inseparable link between the two aspects) are far from being merely intriguing curiosities, but can be transitioned into valuable, real-world technologies with performances that can far exceed those obtainable with classical technologies. The recent demonstration by the Chinese scientists of using a low-earth-orbit satellite to distribute entangled photons to two ground stations that are over a thousand kilometers apart is a stunning technological achievement—direct entanglement distribution over the best available fiber links is limited to a few hundred kilometers—and a harbinger of future possibilities for globally secure communications guaranteed by the power of quantum physics. Harnessing the advantages enabled by superposition, measurement, and entanglement (SME)—the three pillars of quantum physics—for any given application is what is termed quantum engineering in general. In many instances, however, the details of the underlying science (high-temperature superconductivity, photosynthesis, avian navigation, are some examples) is still not fully understood, let alone how to turn the partially understood science into a potentially useful technology. Nevertheless, it has become clear in the last few decades that quantum engineering will require a truly concerted effort that will need to transcend the traditional disciplinary silos in order to create and sustain new breeds of science and technology communities that will be equally versed in quantum physics as they would be in their chosen area of technology. In this talk, I will present my vision for unleashing the potential of quantum engineering, taking quantum communications and networking as an example.

Host:Sharon Weiss

Thursday November 14th 2019 4:00 PM


Deborah Berebichez

Outrageous Acts of Thinking   (show abstract)

Dr. Deborah Berebichez - Debbie is an expert in physics, science, innovation, embracing change, media communications and Internet of Things (IoT) and is an expert in Big Data, acting as a chief Data Scientist in NYC. Debbie is also the cohost of Discovery Channel’s Outrageous Acts of Science TV, where she uses her physics background to explain the science behind extraordinary engineering feats. Deborah has also appeared as an expert on the Travel Chanel, NOVA, CNN, FOX, MSNBC, and numerous international media outlets. She has a Ph.D. in physics from Stanford University: the first Mexican woman ever to do so.

Host:S. Hutson

Monday November 18th 2019 4:00 PM

Mchael Tremmel, Yale University

Hydrodynamic simulations of galaxy formation

Host:K. Holley-Bockelmann

Thursday November 21st 2019 4:00 PM

Andrew Mugler, Purdue

Physics of collective cell sensing   (show abstract)

The physical limits to chemical sensing have been established and tested for single cells. However, recent experiments have demonstrated that cells can surpass these limits when they communicate. The theoretical limits to the precision of collective sensing are still poorly understood. In this talk, I will discuss three types of cell-cell communication (short-range, long-range, and self-communication) and describe how they alter the physical limits for fundamental sensory tasks, including gradient sensing by epithelial organoids and flow sensing by metastatic cancer cells. This work extends the study of sensory limits to multicellular ensembles and lays the blueprint for a generic theory of collective sensing.

Host:W. Holmes

Thursday November 28th 2019 4:00 PM

Thanksgiving Holidays

Thursday December 5th 2019 4:00 PM

Thomas Weiler, Vanderbilt University

Host:S. Hutson

Spring 2020

Thursday January 9th 2020 4:00 PM


Thursday January 16th 2020 4:00 PM


Thursday January 23rd 2020 4:00 PM


Thursday January 30th 2020 4:00 PM


Thursday February 6th 2020 4:00 PM

Zina Cinker, National Graphene Association

Host:N. Tolk

Thursday February 13th 2020 4:00 PM


Thursday February 20th 2020 4:00 PM

Thomas Ullrich, Brookhaven National Laboratory

Host:S. V. Greene

Thursday February 27th 2020 4:00 PM


Thursday March 5th 2020 4:00 PM

Spring Holidays

Thursday March 12th 2020 4:00 PM


Thursday March 19th 2020 4:00 PM

Jeffrey Nico, NIST

Neutron Lifetimes

Host:R. Scherrer

Thursday March 26th 2020 4:00 PM


Thursday April 2nd 2020 4:00 PM


Thursday April 9th 2020 4:00 PM

Saul Teukolsky

Host:R. Scherrer

Thursday April 16th 2020 4:00 PM