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Events During the Week of December 11th through December 18th, 2022

Monday, December 12th, 2022

Preliminary Exam
Superconductor-semiconductor hybrid systems for quantum computing applications
Time: 10:00 am
Place: B343 Sterling
Speaker: Ben Harpt, Physics Graduate Student
Abstract: In the global pursuit to develop quantum computers with unprecedented problem-solving capabilities, success hinges upon engineering platforms that are both controllable and scalable. Superconductors and semiconductors are, individually, among the most promising materials platforms for building a solid-state quantum processor. However, combing the advantages of both materials to build hybrid quantum devices unlocks yet further potential. In this talk, I overview the physics of ‘super-semi’ hybrid systems and discuss how it forms a basis for new technologies in quantum computing. I focus in detail on two diverse applications which are the primary focus of my doctoral research: (1) superconducting resonators used for readout of quantum dot qubits; and (2) qubits formed from Josephson junctions in proximitized germanium heterostructures. In the former example, I show completed work identifying and utilizing a little-known coupling mechanism between the qubit and the resonator. In the latter, I demonstrate early progress toward developing devices and outline a pathway for future research. Studying these and other super-semi hybrid systems offers fruitful new physics and technologies for scaling up quantum computers.
Host: Mark Eriksson
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Plasma Physics (Physics/ECE/NE 922) Seminar
Heat and particle transport in the JET DT2 campaign
Time: 12:00 pm
Place: 1610 Engineering Hall
Speaker: Philip Schneider, IPP Garching
Abstract: Heat and particle transport in tokamak plasmas changes with isotope mass (H, D, T) in such a way that a satisfying theoretical description eludes us to this day.

However, now we at least better understand why we are not able to formulate such a theory. The main ion mass is connected to a large variety of physical mechanisms which will vary in importance for different plasma regimes. The resulting system is determined by the non-linear coupling between transport channels particles and heat, electrons and ions as well as regions within the plasma like the core and the edge (pedestal). In experiments a change of the isotope mass often results in a shift of plasma regime and the isotope mass dependence that you want to measure consequently competes with the impact of variations in other parameters.

The JET tokamak recently dedicated a considerable amount of time to address this issue from multiple angles. A series of dedicated experiments got prepared to ensure that the isotope mass dependencies can be accurately determined. In the edge of H-mode plasmas we find the confinement to scale with mass where H is worst and T best. However, this changes in the core, here H and D are found with matching confinement while T and DT plasmas consistently have better core confinement. Flux-driven simulations with ASTRA using the quasilinear TGLF-SAT2 model and local linear and non-linear gyrokinetic simulations can capture certain aspects of the observation, but also highlight gaps in the models - in particular, with the electromagnetic stabilisation.

Bio
Dr. Philip A. Schneider studied physics at the LMU in Munich did his PhD on tokamak edge transport barriers at the Max-Planck-Institute for Plasma Physics in Germany. He worked the last 14 years on data from ASDEX Upgrade, DIII-D, JET and TCV with a focus on heat transport, confinement and fast ions in tokamak plasmas. Currently, he is coordinator of the task "isotope effects on confinement and transport" in the JET DT2 campaign.
Host: ECE/NE/PHYSICS 922 Seminar in Plasma Physics
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Tuesday, December 13th, 2022

Preliminary Exam
Portal Matter, Kinetic Mixing, and Muon g − 2
Time: 10:00 am
Place: 5280 Chamberlin
Speaker: Ricardo Alexandre Dos Santos Ximenes Filho, Physics Graduate Student
Abstract: We present a minimal toy model construction using leptonic portal matter that addresses the muon g − 2 anomaly through chiral enhancement. While the chiral enhancement mechanism is reminiscent of fermiophobic Z′ gauge models, the parameter space motivated by the kinetic mixing/vector portal dark matter model paradigm is vastly different and readily available to be explored in current and forthcoming experiments. We further explore a detailed realization of this construction that utilizes a SU(2)xSU(2) dark gauge group, that is broken first to a conserved dark U(1) by a Higgs bi-doublet and the dark U(1) is then further broken by a pair of triplet Higgs fields to yield the sub-GeV dark photon.
Host: Lisa Everett
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Thesis Defense
Search for dark matter recoiling from a Higgs boson, which decays to tau lepton pairs, with the CMS detector at the LHC
Time: 1:00 pm - 6:00 pm
Place: 4274 Chamberlin
Speaker: Jithin Madhusudanan Sreekala, Physics Graduate Student
Abstract: This thesis describes search for dark matter particles recoiling from a Higgs boson at the CMS detector at the LHC where the Higgs subsequently decays to two tau leptons. The analysis uses 2017 and 2018 RUN II dataset collected by CMS experiment. This thesis discusses two scenarios, one where taus are resolved and one where taus are boosted.
Host: Sridhara Dasu
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Council Meeting
Time: 3:00 pm - 4:00 pm
Place: 5290 Chamberlin Hall
Speaker: Mark Eriksson, UW-Physics
Host: Mark Eriksson
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Wednesday, December 14th, 2022

Academic Calendar
Deadline for Graduate students to withdraw from the Fall term
Abstract: *Note: actual end time may vary.* CONTACT: 262-3811, registrar@em.wisc.edu URL:
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Academic Calendar
Last class day for fall semester
Abstract: *Note: actual end time may vary.* URL:
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Physics ∩ ML Seminar
Differentiable Programming in HEP
Time: 11:00 am - 12:15 pm
Place: Online Seminar: Please sign up for our mailing list at www.physicsmeetsml.org for zoom link. We will also livestream the talk in Chamberlin 5280.
Speaker: Lukas Heinrich, TU Munich
Abstract: The rise of machine learning within the last decade has to a large degree also been the success of differentiable programming and gradient-based methods both in optimization as well as statistical inference. Going beyond vanilla Deep Learning, differentiable programming allows physicists to inject domain knowledge throughout the ML workflow from adding inductive bias to models via symmetries, using physics models within the loss definition or in defining more informative label data. While this may significantly increase both interpretability and efficiency of ML application in physics, challenges remain in casting key physics processes in the language of differentiable programming - particularly for the deeply hierarchical stochastic processes one observes in high energy physics. In this talk I will review recent advances in applying differentiable programming as a paradigm to HEP and point out new research directions.
Host: Gary Shiu
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Department Meeting
Time: 12:15 pm - 1:00 pm
Place: B343 Sterling Hall
Speaker: Mark Eriksson, UW-Madison, Physics
Monthly Department Meeting
Host: Mark Eriksson
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Outreach
Wednesday Nite @ The Lab
What the heck is x-ray astronomy and why do we bother?
Time: 7:00 pm - 8:00 pm
Place: 1111 Genetics/Biotech or sign up for the zoom link at go.wisc.edu/240r59
Speaker: Dan McCammon, UW–Madison physics
Host: Tom Zinnen
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Thursday, December 15th, 2022

Academic Calendar
Study day
Abstract: *Note: actual end time may vary.* URL:
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R. G. Herb Condensed Matter Seminar
Monolayers and bilayers of the topological semimetal WTe2
Time: 10:00 am - 6:00 pm
Place: 5310 Chamberlin
Speaker: David Cobden, U Washington
Abstract: Layered transition metal chalcogenides have a wide range of electronic properties, and many can readily be exfoliated down to a single monolayer as long as they are kept in an inert atmosphere. In the last few years we have been experimenting with one of these, WTe2, which in the bulk is a semimetal having topological features in its band structure. Monolayers of WTe2 exhibit the edge conduction properties expected of a two-dimensional topological insulator, although the transport properties of the insulating state are puzzling and suggestive of strong electron-hole correlations competing with a superconducting pairing instability. Bilayers show intermediate properties between the monolayer and the metallic bulk, and additionally exhibit sliding ferroelectricity. A number of other interesting phenomena have been associated with this many-faced material in the literature. I will describe our current state of understanding of few layer WTe2 and our attempts to couple it to other 2D materials, including 2D magnets and graphene.
Host: Alex Levchenko
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Searching for UHE Neutrinos with PUEO
Time: 2:30 pm - 6:00 pm
Place: WIPAC (222 W. Washington Ave., 5th floor, Supernova Conference Room)
Speaker: William Luszczak, Ohio State University
Host: Marjon Moulai
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Friday, December 16th, 2022

Academic Calendar
Final exams
Abstract: *Note: actual end time may vary.* URL:
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Department Meeting
Closed Department Meeting
Time: 12:15 pm - 1:00 pm
Place: VIRTUAL - Link will be sent later
Speaker: Mark Eriksson, UW-Madison
Closed meeting to discuss personnel matters—pursuant to Section 19.85(1)(c) of the Wisconsin Open Meetings Law. Virtual Meeting only
Host: Mark Eriksson
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Saturday, December 17th, 2022

Academic Calendar
Final exams
Abstract: *Note: actual end time may vary.* URL:
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Sunday, December 18th, 2022

Academic Calendar
Final exams
Abstract: *Note: actual end time may vary.* URL:
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Academic Calendar
Winter Commencement
Time: 10:00 am - 12:00 am
Abstract: URL:
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