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Events on Monday, February 19th, 2024

Atomic Physics Seminar
Using precision measurements to study the interplay of quantum mechanics and gravity and explore the universe
Time: 12:00 pm - 1:00 pm
Place: 5310 Chamberlin Hall
Speaker: Tejas Deshpande, Northwestern University
Abstract: Gravity is the least understood of the four fundamental forces at a microscopic level. Moreover, quantum phenomena are typically challenging to observe in macroscopic systems. An overlap between gravitational and quantum phenomena is expected to occur at very high energies like those inside a black hole or close to the big bang. Precision measurements offer an alternate low-energy route to studying such phenomena in tabletop experiments. Furthermore, precision measurement tools can be used for cosmic exploration through detection of gravitational waves (GWs) and direct detection of dark matter (DM). In this talk, I will discuss three current experiments aiming to investigate such phenomena of great importance to fundamental physics research. The first experiment involves performing light-pulse atom interferometry (LPAI) over a 100 m vertical baseline and is part of an international collaboration called Matter-wave Atomic Gradiometer Interferometric Sensor (MAGIS). I will discuss the work done by our group at Northwestern University (NU) on the design, construction, and testing of the laser system for MAGIS. I will present empirical and simulation results demonstrating the potential of MAGIS to detect GWs and ultralight DM at mid-band frequencies (0.03-3 Hz) with unprecedented sensitivity. Moreover, I will discuss how MAGIS can study macroscopic quantum phenomena by creating quantum superpositions of massive systems separated by tens of meters. The second experiment aims to use LPAI to measure Newton's gravitational constant, to a precision of less than 10 parts per million, using a 2 m vertical baseline at NU. I will present some recent results from the first stage of the NU apparatus utilizing resonant LPAI, with a record 504 loops, and discuss its implications for MAGIS. The third experiment involves detecting ultralight DM using cryogenic Fabry-Perot cavities at NU. I will conclude with some ideas for near-future experiments which aim to study the interplay of quantum mechanics and gravity using a combination of technologies associated with LPAI, laser interferometry, and kilogram-scale levitation.
Host: Thad Walker
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Plasma Physics (Physics/ECE/NE 922) Seminar
"Coherent structures in non-neutral electron plasmas, 2D fluids, and beyond"
Time: 12:00 pm - 1:15 pm
Place: 1227 Engineering Hall
Speaker: Noah Hurst, WiPPL, UW-Madison Physics Department
Abstract: The self-organization of fluids and plasmas into coherent structures has important consequences for their dynamics and transport, particularly with regard to fusion plasmas and geophysical fluids. Dedicated efforts to understand the life-cycle of these structures are needed, including their formation, dynamics, and stability. Discussed here are a series of experiments with non-neutral pure electron plasmas that follow an interesting trajectory from antimatter technology to studies of coherent vortices in two-dimensional (2D) fluids. The apparatus used for electron plasma vortex dynamics relies on an isomorphism between the plasma ExB drift motion and the 2D ideal fluid equations. The vortices are subjected to external flows to investigate their dynamics and stability, thus recreating in a controlled environment the conditions they might experience in the wild. Experiments are presented regarding vortex oscillations due to applied strain flows, adiabatic vortex behavior in time-dependent strain, spatial Landau damping of vortex modes, the Kelvin-Helmholtz instability within a background strain flow, and the splitting of initially elliptical vortices into multiple pieces. The experimental results are compared to particle-in-cell simulations and simple theoretical models when possible. Finally, opportunities for future work are described involving vortex dynamics, other types of coherent structures in plasmas and fluids, and non-neutral plasma physics.
Host: Physics
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Theory Seminar (High Energy/Cosmology)
Hierarchies from string theory
Time: 4:00 pm - 5:00 pm
Place: 5280 Chamberlin Hall
Speaker: Jakob Moritz, CERN
Abstract: I will explain a series of my works that has resulted in the first ever construction of a controlled cosmological solution of string theory in which the vacuum energy — though negative in sign — is exponentially small, while extra dimensions are microscopic. I will also, in brief terms, outline some of my ongoing efforts to construct solutions with positive vacuum energy. Finally, I will turn to another series of my works about probing string theoretic axions — the string axiverse. I will argue that the strong CP problem is generically absent in string compactifications, and that future observation might well detect string theoretic axions through their couplings to photons.
Host: Lisa Everett
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