Events During the Week of September 15th through September 22nd, 2024
Monday, September 16th, 2024
- Climate & Diversity
- Climate and Diversity Committee Open Hours
- Time: 12:00 pm - 2:00 pm
- Place: Chamberlin 5310
- Speaker: Rachel Zizmann, UW-Madison Physics
- Abstract: Open Hours are welcome for everyone in the department! During these sessions, we have the option to discuss the topic listed, that is not required or necessary for attending
- Host: Rachel Zizmann
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Hot Electron Instabilities in Magnetic Mirrors and Dipoles
- Time: 12:05 pm - 1:00 pm
- Place: 1610 Engineering Hall
- Speaker: Prof. Michael Mauel, Columbia University
- Abstract: The dedication of the new WHAM experiment, having world-record magnetic field strength, has generated renewed interest in magnetic mirror plasma confinement for fusion applications. Beginning in the early 1960's when Ray Dandl (ORNL) discovered how to efficiently couple microwaves near the electron cyclotron frequency to a mirror-confined plasma, several mirror and mirror-like experiments have observed hot electron instabilities. These instabilities are often violent and always beautifully interesting. Common to axisymmetric magnetic mirrors, bumpy tori, and levitated dipoles, hot electron instabilities always appear when the fraction of energetic electrons exceeds some threshold. In contrast, minimum-B magnetic mirrors have only whistler instabilities but do not have hot electron instabilities [Garner, PRL 1987]. When conditions are adjusted so that the hot electron fraction is low, the plasma is much colder and drift instabilities appear. Examples discussed include Shinji Hiroe's "Observation of hot electron ring instabilities in ELMO Bumpy Torus" [POF 1984], observations from the TARA tandem mirror [IAEA-CN-44/CI-4, 1984], from the Collisionless Terrella Experiment [Ben Levitt, POP 2002], and from the Levitated Dipole Experiment [Darren Garnier, POP 2006].
- Host: Cary Forest
Tuesday, September 17th, 2024
- Climate & Diversity
- DEI Lunch and Learn
- How to integrate DEI into faculty and staff hiring process
- Time: 12:00 pm - 1:00 pm
- Place: Zoom
- Speaker: L&S DEI Leadership
Wednesday, September 18th, 2024
- No events scheduled
Thursday, September 19th, 2024
- R. G. Herb Condensed Matter Seminar
- Tunable contributions from charge-rectification and momentum transfer to 1D Coulomb drag
- Time: 10:00 am - 6:00 pm
- Place: 5310 Chamberlin
- Speaker: Dominique Laroche, University of Florida
- Abstract: Coulomb drag is a powerful tool to probe the interaction between closely-spaced low-dimensional systems. Historically, this effect has been understood in terms of momentum transfer between carriers in the two nearby conductors, resulting in a friction-like effect. In one-dimensional systems, Coulomb drag is especially helpful, as single wire conductance measurements seldom yield information on the nature of the Luttinger liquid forming in there strongly confined systems. In this talk, I will present the experimental observation highlighting an alternate drag-inducing mechanism occurring in mesoscopic one-dimensional systems: charge rectification. In contrast to momentum transfer, whose polarity depends on the drive current direction, the charge rectification mechanism consistently generates a drag signal in a given direction, regardless of the drive current direction. After presenting the signatures of this novel drag-inducing mechanism in laterally-coupled quantum wires, I will present our studies of Coulomb drag in vertically-coupled quantum wires separated by a barrier only 15 nm wide. In these vertically coupled devices, fabricated through an Epoxy-Bond-And-Stop-Etch (EBASE) process, notable contributions from both momentum transfer and charge rectification are observed simultaneously. Moreover, the relative strength of both contributions is tunable through both gate voltage and temperature. Through a careful temperature dependence study of the drag signal, we observe a non-monotonic temperature dependence characteristic of Luttinger liquid physics. Furthermore, we confirm the exponential dependence of Coulomb drag with kfd for both charge rectification- and momentum transfer-induced Coulomb drag. This study opens up the possibility of studying the physical mechanisms behind the onset of both momentum transferred and charge rectified drag simultaneously in a single device, ultimately leading to a better understanding of Luttinger liquids in multi-channel wires and paving the way for the creation of energy harvesting devices.
- Host: Alex Levchenko
- Wisconsin Quantum Institute Colloquium
- Quantum systems engineering
- Time: 3:30 pm - 5:00 pm
- Place: Discovery Building, DeLuca Forum
- Speaker: John Martinis, Qolab and UC Santa Barbara
- Abstract:
Quantum computing has entered a compelling scientific era as now quantum algorithms can be run on multiple physical systems. Building even larger machines with error correction is a significant engineering challenge that will require good systems engineering practices. Here I discuss some scientific and technical strategies and ideas that will be important to consider when transitioning from scientific research to development of a complex engineered system. Also considered will be constraints specific to quantum computers, for example the inability to copy information and the need for complex control systems.
This event starts at 3:30pm with refreshments, followed at 3:45pm by a short presentation titled "Fluctuations of Qubit Energy-Relaxation Times: Characterization and Suppression", by Spencer Weeden (McDermott group). The invited presentation starts at 4pm.
- Host: Robert McDermott
Friday, September 20th, 2024
- Physics Department Colloquium
- Exploring Magnetic Reconnection With Phase Space Measurements
- Time: 3:30 pm - 4:30 pm
- Place: Chamberlin 2241
- Speaker: Earl Scime, West Virginia University
- Abstract: One of the “Grand Challenges” of plasma physics is to understand the processes whereby energy stored in the magnetic fields of a plasma is converted into kinetic energy of the ions and electrons in the plasma. We see that this energy conversion happens in stars, in planetary magnetospheres, and in fusion plasmas. Over the past few decades, there has been considerable progress in developing theoretical models of magnetic reconnection, the process responsible for the energy conversion. Measurements from spacecraft and in laboratory experiments have also contributed to our understanding of magnetic reconnection in collisional and collisionless plasmas. Recently, a variant of magnetic reconnection in which ions do not participate and the physics is dominated by electron dynamics has been identified in space measurements – “electron-only reconnection.” I will review the experimental evidence for electron-only reconnection in space and the state of our computational and theoretical understanding of this process. I will also describe recent studies of electron-only reconnection in the PHAse Space MApping (PHASMA) experiment at West Virginia University. In PHASMA, two magnetic flux ropes are driven together to initiate the reconnection process and advanced, non-perturbative diagnostics provide direct measurements of the electron and ion velocity distribution functions at the kinetic scale (at scales smaller than the gyro motion of the charged particles around the magnetic field). We find that, consistent with theoretical predictions, the majority of incoming magnetic energy appears as electron thermal energy and that Ohmic processes are unlikely to be responsible for the measured increase in electron enthalpy. The electron velocity distribution function measurements include non-Maxwellian features, including beams that jet out from the X-point in both outflow directions. We observe that the electron beam speed scales with the local electron Alfvén speed and that the spatial distribution of the electron heating matches theoretical predictions. Measurements of the three-dimensional electron velocity distribution function (a unique capability of the PHASMA facility) confirm that the most likely mechanism for the electron heating is the parallel electric field created in the reconnection process.
- Host: John Sarff
- WiCOR Speaker Event
- Life in the Cosmic Trenches: The Search for Signs of Life Beyond Earth
- Time: 7:00 pm - 8:00 pm
- Place: 1310 Sterling Hall
- Speaker: Sara Seager, Massachusetts Institute of Technology
- Abstract: For thousands of years, inspired by the star-filled dark night sky, people have wondered what lies beyond Earth. Today, the search for signs of life is a key factor in modern-day planetary exploration. Astronomers have found thousands of planets that orbit nearby stars, called "exoplanets". The newly launched James Webb Space telescope will enable us to study gases in rocky exoplanet atmospheres, including gasses that might be attributed to life.
Followed by star-gazing at Washburn Observatory at 8:30 PM. - Host: WiCOR
Saturday, September 21st, 2024
- UW Madison Physics Department Picnic
- Time: 11:00 am - 1:00 pm
- Place: Garner Park, 333 S. Rosa Road
- Abstract: All Physics Picnic! All are welcome - we hope you'll bring spouse, partners, kids! Garner Park has a playground, basketball courts, tennis courts, a big open field for soccer or frisbee. And a shelter - so the picnic will happen, rain or shine! Easy to get to by bike (~4.6 mi from Chamberlin) or by bus (Route A leaves University @ N. Orchard).
- Host: Sharon Kahn
