Physics and Astronomy Colloquia

*Winter Quarter Colloquia Start at 4:00 pm*
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Nate Stern: Playing with Photons in Flatland

September 29, 2017, 4:00 PM - 5:00 PM

Title: Playing with Photons in Flatland

Speaker: Nate Stern, Northwestern University, Department of Physics and Astronomy

Abstract: Light is a powerful tool of science, shaping thoughts of early Greek philosophers and stimulating development of modern electromagnetism, Einstein’s relativity, and quantum mechanics. The quantum conception of light consisting of particles of discrete energy, or photons, underlies its interaction with matter. For solid materials, this understanding has led to transformational applications both as conventional as sensor and display technologies and as extraordinary as lasers. Despite this ubiquity, advances in materials science continue to reveal nuances in the interaction of light with matter. The recent emergence of layered materials of atomic-scale thickness has revealed a rich optical phenomenology such as layer dependent bandgaps and polarization-sensitive transitions that present a new landscape in which to play with the coupling to photons. In this presentation, I will discuss new regimes of interactions between light and two-dimensional sheets of atoms. I will describe top-down nanopatterning of atomically-thin crystals and their integration with photonic devices to engineer their electromagnetic environment. Harnessing the symmetry of monolayer crystals, we realize spin-polarized exciton-polariton quasi-particles, quantum superpositions that are ‘half-light’ and ‘half-matter’, with properties distinct from either constituent. These examples suggest potential for new coherent quantum optical phenomena and opto-electronic applications that harness the unique properties of low-dimensional nanomaterials.

Host: Stern

Speaker Schedule

Keywords: Physics, Astronomy, colloquium


Title: Precision Spectroscopy of Atomic Hydrogen and the Proton Radius Puzzle

Speaker: Thomas Udem, Max-Planck Institut fuer Quantenoptik

Abstract: Precise determination of transition frequencies of simple atomic systems are required for a number of fundamental applications such as tests of quantum electrodynamics (QED), the determination of fundamental constants and nuclear charge radii. The sharpest transition in atomic hydrogen occurs between the metastable 2S state and the 1S ground state with a natural line width of only 1.3 Hz. Its transition frequency has now been measured with almost 15 digits accuracy using an optical frequency comb and a cesium atomic clock as a reference [1]. A recent measurement of the Lamb shift in muonic hydrogen is in signicant contradiction to the hydrogen data if QED calculations are assumed to be correct [2]. In order to shed light on this discrepancy the transition frequency of one of the broader lines in atomic hydrogen has to be measured with very good accuracy. For this purpose we have employed our previous 1S-2S apparatus as a cold source of laser excited 2S atoms in order to perform spectroscopy on the 2S-4P transitions. With a natural line width of 12.7 MHz, large Doppler eects, quantum interference etc. a good line shape analysis is mandatory to identify the true transition frequency. Analyzing our initial data yields a proton radius that is compatible with the value obtained from muonic hydrogen with an uncertainty comparable to the previous hydrogen world data.

Host: Gabrielse

Speaker Schedule

Keywords: Physics, Astronomy, colloquium


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TBA: TBA

October 13, 2017, 4:00 PM - 5:00 PM

Title: TBA

Speaker: TBA

Abstract: 

Host: Hahn

Speaker Schedule

Keywords: Physics, Astronomy, colloquium


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TBA: TBA

October 20, 2017, 4:00 PM - 5:00 PM

Title: TBA

Speaker: TBA

Abstract: 

Host: Dahl

Speaker Schedule

Keywords: Physics, Astronomy, colloquium