Upcoming Events For Colloquia

Exoplanet imaging with extremely large telescopes: A new era of detailed exoplanet characterization

Dr. Rebecca Jensen-Clem
Postdoctoral Research Fellow
Department of Astronomy,  UC Berkeley

In the last thirty years, over 3000 planets have been discovered orbiting nearby stars. This flood of new worlds includes planets unlike any found in our own Solar System, from Jupiter-mass planets with years as short as our day to exotic rocky worlds twice as massive as the Earth. While our understanding of exoplanets' diversity has leapt forward in recent years, fundamental questions remain. For example, what are the dominant planet formation pathways? How do planets acquire their atmospheres? Is there life on other worlds? These questions can only be answered through observations of exoplanets’ spectra, where the characteristic imprints of atoms and molecules making up a planet’s atmosphere are revealed. The most promising method for obtaining spectra of diverse exoplanets is direct imaging: by nulling the light of the parent star with an optical device called a coronagraph, the planet itself can be seen and its light dispersed into a spectrum. So far, only extremely young, massive worlds have been directly imaged, while older, lower mass objects like the Earth remain hidden in the glare of their host stars. In this talk, I will describe two avenues for advancing the state-of-the-art in exoplanet imaging: 1) detecting low-mass exoplanets at Solar System separations with the W. M. Keck Observatory and Thirty Meter Telescope via predictive wavefront control, and 2) characterizing the atmospheres of directly imaged planets with polarimetry -- an untapped method for probing the physics of clouds in the atmospheres of other worlds.

Excitons in Flatland: Exploring and manipulating many-body effects on the optical excitations in quasi-2D materials

Dr. Diana Qiu
Postdoctoral Researcher, UC Berkeley
and Materials Science Division, Lawrence Berkeley National Laboratory

Since the isolation of graphene in 2004, atomically-thin quasi-two-dimensional (quasi-2D) materials have proven to be an exciting platform for both applications in novel devices and exploring fundamental phenomena arising in low dimensions. This interesting low- dimensional behavior is a consequence of the combined effects of quantum confinement and stronger electron-electron correlations due to reduced screening. In this talk, I will discuss how the optical excitations (excitons) in quasi-2D materials, such as monolayer transition metal dichalcogenides and few-layer black phosphorus, differ from typical bulk materials. In particular, quasi-2D materials are host to a wide-variety of strongly-bound excitons with unusual excitation spectra and massless dispersion. The presence of these excitons can greatly enhance both linear and nonlinear response compared to bulk materials, making them ideal candidates for optoelectronics and energy applications. Moreover, due to enhanced correlations and environmental sensitivity, the electronic and optical properties of these materials can be easily tuned. I will discuss how substrate engineering, stacking of different layers, and the introduction or removal of defects can be used to tune the band gaps and optical selection rules in quasi-2D materials.

Revealing and harnessing exotic emergent phenomena in entangled quantum matter

Dr. Ryan Mishmash
Postdoctoral Researcher
UC Berkeley

Emergence and entanglement are two central concepts in the field of modern quantum condensed matter physics. Emergence was popularized nearly a half-century ago by P.W. Anderson: the collective low-energy behavior of an interacting many-body system can exhibit behavior profoundly different from that of the constituent degrees of freedom. Entanglement, while a more recent notion in the context of the many-body problem, is equally important: in essence, it quantifies the "quantumness" of the system of interest. In this talk, I will present recent work on two paradigmatic quantum condensed matter systems in which these two concepts play a defining role. First, I will discuss a spin model on the 2D kagome lattice relevant to a number of layered experimental compounds. Through large-scale entanglement-based numerical simulations and field-theoretic analysis, we find intriguing evidence for emergent fermions and an associated emergent gauge field arising at low energies in this system [1]. Next, I will turn to the half-filled Landau level and present two studies [2,3] in which we have employed large-scale numerical calculations to shed light on various recent theoretical and experimental quandaries of this classic albeit enigmatic problem. I will conclude by briefly mentioning one closely related example in which emergent quantum phenomena have enormous potential to be harnessed for technological gain, namely how "Majorana zero modes" can be used to build superior quantum computing hardware. Several directions of future research in these areas will be discussed.
[1] A. M-Aghaei, B. Bauer, K. Shtengel, and RVM, PRB 98, 054430 (2018)
[2] RVM and O. I. Motrunich, PRB 94, 081110(R) (2016)
[3] RVM, D. F. Mross, J. Alicea, and O. I. Motrunich, PRB 98, 081107(R) (2018)

Title TBA

Dr. Timothy Linden
Postdoctoral Fellow
Department of Physics
The Ohio State University…

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Dr. James Garrison
Joint Quantum Institute at the University of Maryland…

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Dr. Yue Zhang
Postdoctoral Fellow, COFI Scholar
Fermilab/Northwestern University…

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Dr. Chao-Ming Jian
Kavli Institute for Theoretical Physics
UC Santa Barbara…

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Dr. Susanne Westhoff
Heidelberg…

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Dr. Simon Knapen
Institute for Advanced Study…

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Dr. Zhen Liu
Postdoctoral Associate
Department of Physics
University of Maryland…

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Dr. Yuhsin Tsai
Postdoctoral Associate
Department of Physics
University of Maryland…

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Prof. Ned Wingreen
Howard A. Prior Professor in the Life Sciences
Professor of Molecular Biology and the Lewis-Sigler Institute for Integrative Genomics
Associate Director, Lewis-Sigler Institute for Integrative Genomics
Princeton University

Hosted by Prof. Janko…