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Events During the Week of October 23rd through October 30th, 2022

Monday, October 24th, 2022

Plasma Physics (Physics/ECE/NE 922) Seminar
Exploring the new electron-positron plasma frontier: the annihilation signature of cold magnetically-confined pairs and accessing the relativistic and magnetized regime
Time: 12:00 pm
Place: 1610 Engineering Hall
Speaker: Jens von der Linden, IPP Garching
Abstract: Advances in positron production, accumulation, and trapping are enabling a new plasma physics frontier: electron-positron pair plasma. I will report on two parallel efforts.

One line of research aims to accumulate and magnetically confine moderated positrons with electrons in sufficient numbers to produce a pair plasma with a small Debye length (but with a skin depth exceeding the plasma size). The mass symmetry of pair plasma has led to many predictions with regard to their stability to electrostatic modes and (absence of) turbulence. Yet, it is unclear how to diagnose the behaviour of these electromagnetically transparent plasmas without terminating them. Here, I show that direct annihilation in the bulk of the plasma, positronium formation and subsequent annihilation, as well as transport to the wall and magnets will produce various volumetric and localized sources of gamma emission with rates related to the plasma parameters. Methods for diagnosing and differentiating between volumetric and localized gamma sources are developed.

The other effort aims to magnetize the large numbers (up to 10^12) of pairs produced through laser-target interactions at intense short-pulse laser facilities. The energy of these pair beams can be controlled by manipulating the sheath on the backside of the target. The charge ratio of the pair beam can be made unitary with magnetic collimation. The lifetime of these pair beams can be extended with magnetic mirror trapping. Together, these experimental techniques could make the relativistic and magnetized plasma regime, prevalent around massive astrophysical objects such as magnetars, accessible.

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Wisconsin Quantum Institute
Molecular Quantum Photonics
Time: 1:30 pm
Place: 2401 Chemistry (enter in new North Tower, 2nd floor)
Speaker: Alex S. Clark, Quantum Engineering Technology Labs, University of Bristol
Abstract: Single organic molecules have recently seen increased interest for use as single photon sources [1]. They emit photons with high efficiency and at favourable wavelengths for coupling to other quantum systems, such as alkali atoms [2]. I will present our recent work on growing various mixed molecular crystals [3,4] which show promise for interfacing with rubidium and potassium atoms. I will discuss methods that can be used to tune molecule emission via both applied electric fields and the application of strain [5]. We have recently shown that subsequent photons emitted by a single molecule can undergo quantum interference at a beam splitter [6], which is a useful tool in optical quantum computing and communication. I will discuss how the indistinguishability of photons can not only be ascertained employing pulsed excitation, which is commonly carried out for single quantum emitters, but can also be found via continuous wave excitation as long as measurements are carried out at more than one excitation power. While the excitation of molecules and their subsequent radiative emission is efficient [7], the generated photons can be difficult to collect. There is therefore a large amount of ongoing work on coupling organic molecules to nanophotonic structures to modify their emission. The simplest photonic structure one can imagine is an integrated optical waveguide. I will discuss methods to deposit and evanescently couple molecules to waveguides, and present a hybrid plasmonic structure that has shown recent promise [8]. Evanescent coupling has limitations as the molecules cannot sit at the maximum of the vacuum electric field of the waveguide. I will present our recent work on coupling molecules to interrupted waveguides using on chip micro-capillaries [9]. Finally, I will discuss our future plans to couple molecules to enhance this coupling through the use of nanophotonic cavities.

[1] C. Toninelli et al., Nature Materials 20, 1615-1628 (2021).
[2] P. Siyushev et al., Nature 509, 66-70 (2014).
[3] R. C. Schofield et al., Optical Materials Express 10, 1586-1596 (2020).
[4] R. C. Schofield et al., ChemPhysChem 23, e202100809 (2022).
[5] A. Fasoulakis et al., submitted (2022).
[6] R. C. Schofield et al., Phys. Rev. Research 4, 013037 (2022).
[7] P. Ren et al., Chinese Physics Letters 20, 073602 (2022).
[8] S. Grandi et al., APL Photonics 4, 086101 (2019).
[9] S. Boissier et al., Nature Commun. 12, 706 (2021).
Host: Randall Goldsmith, Chemistry
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Tuesday, October 25th, 2022

Theory Seminar (High Energy/Cosmology)
Axion wind detection with the homogeneous precession domain of superfluid helium-3
Time: 4:00 pm
Place: Chamberlin 5280
Speaker: Christina Gao, Illinois U., Urbana
Abstract: Axions and axion-like particles may couple to nuclear spins like a weak oscillating effective magnetic field. Existing proposals for detecting this "axion wind" sourced by dark matter exploit analogies to nuclear magnetic resonance (NMR) and aim to detect the small transverse field generated when the axion wind resonantly tips the precessing spins in a polarized sample of material. In this talk, I will describe a new proposal using the homogeneous precession domain of superfluid He-3 as the detection medium, where the effect of the axion wind is a small shift in the precession frequency of a large-amplitude NMR signal. This setup can provide broadband detection of multiple axion masses simultaneously, and has competitive sensitivity to other axion wind experiments such as CASPEr-Wind at masses below 0.1 micro-eV by exploiting precision frequency metrology in the readout stage.
Host: George Wojcik
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Wednesday, October 26th, 2022

No events scheduled

Thursday, October 27th, 2022

R. G. Herb Condensed Matter Seminar
2D Electronics, Layer by Layer
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Shawna Hollen, UNH
Abstract: Two-dimensional materials now form the basis for a broad and rich field of research bristling with exciting possible applications from photonics to quantum computing and leading to discoveries of new phenomena due to the high customizability of the materials systems and interactions within them. Research in the Hollen lab focuses on understanding the role of defects, disorder, and interlayer interactions in determining the electronic properties of 2D crystals using scanning tunneling microscopy (STM). In this talk, I will focus on projects where we are studying the degradation of 2D layers at the atomic scale, the role of dynamics and interlayer interactions in determining a collective ground state, and extending our experimental tools to nanosecond time-resolution.
Host: Victor Brar
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Astronomy Colloquium
White Dwarf Binaries across the H-R diagram
Time: 3:30 pm
Place: Sterling Hall 4421
Speaker: Dr. Borja Anguiano, University of Notre Dame
Abstract: The evolution of multiple-star systems is a fundamental question in stellar astrophysics where around 25% of the binary systems are compact enough to exchange mass, changing the structures and subsequent evolution of both stars. Muti-object-wavelength-epoch massive stellar spectroscopic surveys are opening a new era to study the properties of compact binaries across the H-R diagram. In this talk I discuss the recent APOGEE-GALEX-Gaia Catalog (AGGC) of candidate compact binaries containing potential WD stars. Numbering over 3400 sources, the size of this catalog is comparable to that of previous WDMS catalogs but includes secondary companions in the MS, subgiant branch, RGB, and red clump (RC) phases of evolution, as well as systems that occupy the MS binary and sub-subgiant (SSG) regions of the H-R diagram.

Also via zoom
Host: Ke Zhang
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Friday, October 28th, 2022

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Powerful Indirect Constraints on the Origins of Ultra High Energy Cosmic Rays
Time: 2:00 pm
Place: CH 4274
Speaker: Glennys Farrar, NYU
Abstract: As is now painfully evident, finding the sources of UHECRs is very challenging due to the combination of most UHECRs having intermediate masses, the poor precision in individual UHECR charge assignments, and generally large deflections in the imperfectly-known Galactic magnetic field. These effects not only smear the images of individual UHECR sources but also lead to a non-trivial and poorly-constrained mapping between a source's direction and the arrival direction distribution of its UHECRs. In the face of this challenge, indirect information on the sources which is imprinted on the spectrum and composition of UHECRs as they emerge from the source surroundings and on the neutrinos they produce, provides valuable additional information on the nature of the sources. This talk will discuss the resulting constraints on the physical properties of the environment surrounding the source, and a possible picture that emerges when also considering evidence on the number density and diversity of source types.
Host: Lu Lu
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Physics Department Colloquium
The seemingly-anomalous magnetic moment of the muon - a novel reconciliation with the Standard Model and connection with Dark Matter
Time: 3:30 pm
Place: 2241 Chamberlin Hall
Speaker: Glennys Farrar, NYU
Abstract: Precision measurement of the magnetic moment of the muon yields a result 4.2 sigma above the prediction of the Standard Model. At the same time, the lattice QCD calculation of the “hadronic vacuum polarization” — essentially, a weighted integral of the cross section for e+e- -> hadrons — disagrees with the direct experimental measurement at a similar level. I will propose that both discrepancies can be explained, quite naturally, by production of unseen final states in e+e- -> hadrons. Such so-far-undiscovered hadrons have to be neutral and long-lived to have escaped detection, and in fact could be the Dark Matter particle. I will discuss tests of this proposal.
Host: Lu Lu
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