Events at Physics

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Monday, February 7th, 2022

Special Talk at WID Orchard Room , Sarah Horst, Johns Hopkins University
Planets in a Bottle: The Role of Laboratory Experiments in the Search for Life
Time: 9:00 am
Place: Wisconsin Institutes for Discovery, Orchard Room
Speaker: Sara Horst, Johns Hopkins Unversity
Abstract: From exoplanets, with their surprising lack of spectral features, to Titan and its characteristic haze layer, numerous planetary atmospheres may possess photochemically produced particles of "haze". With few exceptions, we lack strong observational constraints (in situ or remote sensing) on the size, shape, density, and composition of these particles. Photochemical models, which can generally explain the observed abundances of smaller, gas phase molecules, are not well suited for investigations of much larger, solid phase particles. Laboratory investigations of haze formation in planetary atmospheres therefore play a key role in improving our understanding of the formation and composition of haze particles. I will discuss a series of experiments aimed at improving our understanding of the physical and chemical properties of planetary atmospheric hazes for a wide range of exoplanets including super-Earths, and mini-Neptunes and how we hope to use our results to aid in the search for life.

Host: Susanna Widicus Weaver, Vozza Professor of Chemistry and Astronomy

Tuesday, February 8th, 2022

R. G. Herb Condensed Matter Seminar
Novel optical probes in the study of condensed matter systems
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: Ilya Esterlis, Harvard University
Abstract: A great deal of our understanding of condensed matter comes from observing how materials interact with light. In recent years, the development of novel optical probes has opened yet a new route by which to investigate condensed matter systems, allowing to both interrogate interesting materials that are challenging to study by conventional means and also yielding information in complementary parameter regimes. I will focus on two such probes: exciton spectroscopy in 2D semiconductors and sensing with nitrogen-vacancy (NV) centers in diamond. As a concrete demonstration, I will describe (1) how these probes have been utilized to establish the existence of Wigner crystal phases — the solid phase of the interacting electron gas — in 2D transition-metal dichalcogenide (TMD) systems and (2) how they may further elucidate properties of the electron solid and also shed light on the nature of the corresponding liquid-solid transition, where effects such as frustrated magnetism and impurity interactions are expected to result in exotic and fascinating physics. Finally, I will provide some outlook on the promise of these techniques to investigate more general classes of interesting condensed matter systems.
Host: Robert McDermott
Council Meeting
Physics Council Meeting
Time: 4:00 pm
Place: 2314 Chamberlin
Speaker: Eriksson, UW-Madison, Department of Physics
Host: Eriksson

Wednesday, February 9th, 2022

Physics ∩ ML Seminar
Probabilistic Deep Learning and Applications to FRB parameter inference
Time: 11:00 am
Place: 5280 Chamberlin
Abstract: Probabilistic Deep Learning is a powerful tool that combines predictive power of deep learning algorithms with rigorous statistical methods for inferring complex relations in stochastic data. The talk will first give an introduction to probabilistic DL with review of the most popular frameworks, and then an application of presented methods to the inference of properties of Fast Radio Bursts.

Thursday, February 10th, 2022

R. G. Herb Condensed Matter Seminar
NISQ: Error Correction, Mitigation, and Noise Simulation
Time: 10:00 am
Place: virtual:
Speaker: Bei Zeng, The Hong Kong University of Science and Technology
Abstract: Error-correcting codes were invented to correct errors on noisy communication channels. Quantum error correction (QEC), however, may have a wider range of uses, including information transmission, quantum simulation/computation, and fault-tolerance. These invite us to rethink QEC, in particular, about the role that quantum physics plays in terms of encoding and decoding. The fact that many quantum algorithms, especially near-term hybrid quantum-classical algorithms, only use limited types of local measurements on quantum states, leads to various new techniques called Quantum Error Mitigation (QEM). This work addresses the differences and connections between QEC and QEM, by examining different application scenarios. We demonstrate that QEM protocols, which aim to recover the output density matrix, from a quantum circuit do not always preserve important quantum resources, such as entanglement with another party. We then discuss the implications of noise invertibility on the task of error mitigation, and give an explicit construction called quasi-inverse for non-invertible noise, which is trace-preserving while the Moore-Penrose pseudoinverse may not be. We also study the consequences of erroneously characterizing the noise channels, and derive conditions when a QEM protocol can reduce the noise. virtual:
Host: Mark Saffman

Friday, February 11th, 2022

Theory Seminar (High Energy/Cosmology)
A Puncture in the Euclidean Black Hole
Time: 1:00 pm
Place: Chamberlin 5280
Speaker: Yoav Zigdon, Ben-Gurion University of the Negev
Abstract: We consider the backreaction of the winding zero mode on the cigar geometry. We focus on the case of the $SL(2,R)_k/U(1)$ cigar associated with e.g. the near-horizon limit of k NS5 black-branes. We solve the equations of motion numerically in the large k limit as a function of the amplitude of the winding mode at infinity. We find that there is a critical amplitude $A_c=\exp(-\gamma/2)$ that admits a critical solution. In string theory, the exact CFT description of the $SL(2,R)_k/U(1)$ cigar, fixes completely the winding amplitude, $A_s$, at infinity. We find that in the large $k$ limit there is an exact agreement $A_c=A_s$. The critical solution is a cigar with a puncture at its tip; consequently, the black hole entropy is carried entirely by the winding condensate. We comment on the Lorentzian interpretation of the solution.
Host: George Wojcik