Events at Physics
Events on 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.
- Wisconsin Quantum Institute
- Actions to advance equity, diversity, and inclusion in science
- Time: 1:00 pm
- Place: Zoom (registration required)
- Speaker: Candace Harris + Rowan Thomson, Carleton University
- Abstract: There's growing awareness of the lack of diversity in science and the presence of barriers to inclusion. What factors lead to disparities in representation? Why should we be motivated to effect change? What can we do to change things? Will our actions really make a difference?
This presentation will focus on ideas to challenge the status quo – actions to advance equity, diversity, and inclusion (EDI). We will discuss recent research to illustrate and raise awareness of the many EDI challenges in science, then explore various practical ways to take action to advance EDI. These practical actions stem from our recently released "Science is For Everyone" Teaching toolkit, which provides an abundance of ideas to diversify science education and further support recruitment, retention, and advancement of all students. We will touch on the importance of diversifying content and talk about how Indigenous content is being brought into post-secondary science courses. Finally, we will give an overview of other exciting science EDI initiatives across research and academic life.
Zoom Registration required:
- Host: Institute for Quantum Computing
- 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 . They emit photons with high efficiency and at favourable wavelengths for coupling to other quantum systems, such as alkali atoms . 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 . We have recently shown that subsequent photons emitted by a single molecule can undergo quantum interference at a beam splitter , 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 , 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 . 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 . Finally, I will discuss our future plans to couple molecules to enhance this coupling through the use of nanophotonic cavities.
 C. Toninelli et al., Nature Materials 20, 1615-1628 (2021).
 P. Siyushev et al., Nature 509, 66-70 (2014).
 R. C. Schofield et al., Optical Materials Express 10, 1586-1596 (2020).
 R. C. Schofield et al., ChemPhysChem 23, e202100809 (2022).
 A. Fasoulakis et al., submitted (2022).
 R. C. Schofield et al., Phys. Rev. Research 4, 013037 (2022).
 P. Ren et al., Chinese Physics Letters 20, 073602 (2022).
 S. Grandi et al., APL Photonics 4, 086101 (2019).
 S. Boissier et al., Nature Commun. 12, 706 (2021).
- Host: Randall Goldsmith, Chemistry