Events at Physics |
Events During the Week of December 10th through December 17th, 2023
Monday, December 11th, 2023
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Fusion-relevant studies using the LAPD: ICRF and mirror physics
- Time: 12:00 pm - 1:15 pm
- Place: 1610 Engineering Hall
- Speaker: Dr. Troy Carter, Director of Basic Plasma Science Facility (BaPSF) at UCLA
- Abstract: The Basic Plasma Science Facility (BaPSF) at UCLA is a US national collaborative research facility for studies of fundamental processes in magnetized plasmas supported by DOE FES and NSF. The centerpiece of the facility is the Large Plasma Device (LAPD), a 20m long, magnetized linear plasma device. LAPD has been utilized to study a number of fundamental processes, including: collisionless shocks, dispersion and damping of kinetic and inertial Alfvén waves, compressional Alfvén waves for ion-cyclotron range of frequencies heating, flux ropes and magnetic reconnection, three-wave interactions and parametric instabilities of Alfvén waves, turbulence and transport and interactions of energetic ions and electrons with plasma waves. An overview of research using the facility will be given, followed by a more detailed discussion of fusion- and mirror-relevant studies. These include our "ICRF Campaign," focused on wave physics and parasitic effects relevant to ion cyclotron range of frequencies (ICRF) heating and current drive in fusion devices. This includes high power (~ 200kW) fast wave excitation (ω ∼ 2−10Ωci) experiments that have the structure and scaling of RF sheaths, the formation of convective cells and associated density modification, as well as low power experiments documenting parasitic coupling to the slow mode and the interaction of high-harmonic fast waves (or helicon waves) with filamentary structures to study turbulent scattering processes. LAPD has a flexible magnetic field configuration, allowing for mirror configurations with variable mirror ratio, including periodic (many cell) mirrors. Changes to turbulence and turbulent transport have been documented as a function of mirror ratio. In a single-celled mirror, density and magnetic field fluctuation amplitudes decreased with increasing mirror ratio, while potential fluctuation amplitudes remained similar. The cross-phase between potential and density fluctuations varies with increasing mirror ratio, suggesting a shift in the underlying linear instability as the mirror ratio is increased and magnetic curvature is introduced.
Bio:
Troy Carter is a Professor of Physics at the University of California, Los Angeles. Prof. Carter is the Director of the Basic Plasma Science Facility (BaPSF), a national user facility for plasma science supported by DOE and NSF. He is also the Director of the Plasma Science and Technology Institute (PSTI), an organized research unit at UCLA. His research into waves, instabilities, turbulence and transport in magnetically confined plasmas is motivated by the desire to understand processes in space and astrophysical plasmas as well as by the need to develop carbon-free electricity generation via nuclear fusion. Prof. Carter led the DOE FESAC Long Range Planning process that resulted in the 2021 report “Powering the Future: Fusion and Plasmas.” He is a Fellow of the APS and is a recipient of the APS DPP John Dawson Excellence in Plasma Physics Research Award and of the Fusion Power Associates Leadership Award. Prof. Carter received BS degrees in Physics and Nuclear Engineering from North Carolina State University in 1995 and a PhD in Astrophysical Sciences from Princeton University in 2001. - Host: Prof. Steffi Diem
- Thesis Defense
- Discovery, Demographics, and Dark Matter Implications of Faint Dwarf Galaxies in Wide-area Optical Surveys
- Time: 12:00 pm
- Place: B343 Sterling
- Speaker: Mitch McNanna, Physics PhD Graduate Student
- Abstract: The combined sky coverage and depth of modern wide-area ground-based optical imaging surveys, in particular the Dark Energy Survey, have made possible the discovery and cataloging of the least luminous known galaxies. The demographics of faint dwarf galaxies throughout our local environment and the properties of the smallest individual ultrafaint galaxies have broad implications for astrophysics. I have designed and implemented search algorithms to identify faint dwarf galaxies both within the gravitational influence of the Milky Way and beyond out to the edges of the Local Group. The census of ultrafaint Milky Way satellites has placed competitive constraints on several alternative dark matter models, established the importance of the Large Magellanic Cloud in the formation of our local galactic environment, and increased our understanding of the connection between the smallest galaxies and the dark matter halos that host them. The search for faint field dwarf galaxies beyond the Milky Way uncovered one of the most diffuse dwarf galaxies ever discovered, the largest galaxy known at its luminosity. By comparing the current catalog of nearby dwarf galaxies to the results of searches over simulated versions of the Local Group, I conclude that we have likely exhausted the power of searches for resolved stellar populations in current wide-area sky coverage. Looking forward, this work informs what we might expect to discover in future surveys covering new areas of sky or with deeper data and how these discoveries will change our understanding of the particle properties of dark matter and the nature of galaxy formation.
- Host: Keith Bechtol
Tuesday, December 12th, 2023
- Preliminary Exam
- Subatomic to Supernova: Two unrelated tales of neutrinos and dark matter
- Time: 12:30 pm - 6:00 pm
- Place: 2314 Chamberlin
- Speaker: Daniel Heimsoth, Physics PhD Graduate Student
- Abstract: I will present my work on two recent papers. First, supernovae expel a large fraction of their energy in neutrinos, making them a potentially useful detection channel to understand properties of stellar core collapse. With the construction of new, larger neutrino experiments such as Hyper-Kamiokande, DUNE, and IceCube Gen2 in the near future, we will have the capability to measure the time-dependent neutrino flux from nearby core-collapse supernovae. I will show how using the neutrino signal from a theorized hadron-quark phase transition during core collapse can allow us to not only triangulate the position of the supernova in the sky to good precision but also set limits on the absolute neutrino mass scale.
Turning our attention from neutrinos to dark matter, I will then describe my work on quantifying uncertainties in direct detection dark matter experiments stemming from uncertainties in nuclear modeling. As these experiments shift from considering only the spin-independent and spin-dependent operators to a complete set of operators coupling dark matter to nuclei, it becomes especially important to understand all sources of uncertainty. I will explain how we calculated the nuclear model uncertainties for xenon, a common choice of target in direct detection experiments, and how these uncertainties can be significantly large for certain operators. - Host: Baha Balantekin
- Thesis Defense
- Synthetic Source Injection in The Dark Energy Survey: Measurements of the Survey Transfer Function and Applications to Precision Cosmology
- Time: 2:00 pm - 6:00 pm
- Place: B343 Sterling
- Speaker: Megan Tabbutt, Physics PhD Graduate Student
- Abstract: Presented here is the Dark Energy Survey’s (DES) Synthetic Source Injection (SSI) methodology and applications to precision cosmology for our Y6 analysis of large-scale structure. Our methodology is predicated on injecting models of real objects obtained from our very high signal-to-noise Deep Field observations into our single-epoch wide field images Both of which are critical to the measurements of the three 2-point correlation functions, cosmic shear, galaxy clustering and galaxy-galaxy lensing, from which we constrain cosmological parameters. This methodology was introduced for our Y3 analysis, and was the first example of using SSI to directly calibrate the cosmological measurements from a WF survey. The refinement and expansion of the methodology is presented here. Specifically, we improved our mirroring of the WF image processing pipeline to now fully recreate it. We refactored our code-base to be able to run our SSI at multiple super-computing centers, minimizing wall time and maximizing allocations. We also developed a new injection scheme that injects sources which are preferentially more useful to the cosmological analyses. These as well as other updates, our initial Y6 SSI results, and their applications to precision cosmology will be discussed at length in this thesis. which are then processed identically to the original wide images. Inherent to this methodology, is that the synthetic sources automatically inherit the same systematics of the real wide field data, a highly sought after achievement for many systematics modeling pipelines that is nearly impossible to achieve from forward modeling techniques alone. In the end, we obtain wide field photometry catalogs of the deep field objects including their inheritance of the systematics. These catalogs are a Monte Carlo sampling of the transfer function of the survey and can be used for calibration and diagnostics, as well as aid in the calculation and validation of our 3x2pt analysis and consequentially our measurement of cosmological parameter constraints. Specifically, through the photometric redshift calibration of the weak lensing sources and the magnification bias estimate for the lens galaxy samples.
- Host: Keith Bechtol
- Network in Neutrinos, Nuclear Astrophysics, and Symmetries (N3AS) Seminar
- Finding the neutrino mass mechanism at muon colliders
- Time: 2:00 pm
- Place: Join Zoom Meeting Meeting ID: 912 3071 4547
- Speaker: Kåre Fridell , KEK, Tsukuba
- Abstract: In this talk I will show how neutrino mass mechanisms may be probed in
future muon colliders, with special emphasis on the proposed μTRISTAN
experiment. If neutrinos are Majorana particles, they may lead to
charged lepton flavor violating processes that would constitute clear
evidence for New Physics in the lepton sector. Using an effective field
theory framework, we then compare the potential discovery reach with
existing limits from rare lepton decays, finding that muon colliders are
the most sensitive probe of charged lepton flavor violation for a range
of parameters. As a model example, we then consider the type-ii seesaw
model, and show how a muon collider could be used to constrain the CP-
violating phases of the corresponding PMNS matrix.
- Host: Baha Balantekin
Wednesday, December 13th, 2023
- Academic Calendar
- Last Fall Semester class day
- Abstract: *Note: actual end time may vary.* URL:
- Thesis Defense
- Naturalness Demands an Answer: The Imperative of Natural SUSY at the HL-LHC
- Time: 11:00 am - 1:00 pm
- Place: 5310 CH
- Speaker: Kairui Zhang, Physics PhD Graduate Student
- Abstract: We explore the ramifications of natural supersymmetry (natSUSY) frameworks for upcoming experiments at the high-luminosity Large Hadron Collider (HL-LHC). Specifically, we scrutinize the production and subsequent decay modes of heavy SUSY Higgs bosons, both neutral and charged, as well as stop pairs and electroweakino pairs, within the context of natural SUSY. The study highlights the importance of decay hierarchy and the potential existence of a light higgsino for accurate interpretation of LHC data. A detailed examination reveals that the dominant decay modes of heavy winos to Standard Model bosons—W, Z, or h—alongside light higgsinos with weak-scale masses, emerge as a unique signature of the natural SUSY paradigm. The investigation delineates both the discovery and exclusion limits for these heavy SUSY particles, thereby offering critical insights into the viability and constraints of natural SUSY models in the forthcoming LHC runs.
- Host: Vernon Barger
- Department Meeting
- Closed Department Meeting
- Time: 12:15 pm - 1:15 pm
- Place: B343 Sterling
- Speaker: ERIKSSON, UW - Madison
- Closed meeting to discuss personnel matters—pursuant to Section 19.85(1)(c) of the Wisconsin Open Meetings Law
- Preliminary Exam
- A Search for Vector-Like Leptons (VLLs)
- Time: 2:30 pm - 4:30 pm
- Place: 4272 Chamberlin
- Speaker: Elise Chavez, Physics PhD Graduate Student
- Abstract: The Standard Model is the current theoretical description of fundamental particles and their interactions. While it is able to describe the majority of phenomena that we observe, there are many that it cannot accommodate for. Such phenomena are dark matter, dark energy, and lepton non-universality. New theories have been proposed that extend the Standard Model in order to answer these long standing questions. One such extension is the 4321 model that predicts several new particles, one of which is the vector-like lepton (VLL). A search for pair produced vector-like leptons (VLLs) is proposed using the Run II data that was produced by proton-proton collisions at sqrt(s) = 13 TeV and collected by the Compact Muon Solenoid (CMS) at the Large Hadron Collider (LHC). In this search, the modes where the decays of the VLLs result in two Standard Model leptons are examined. This search employs a set of optimized kinematic selection criteria to enhance the signal, with respect to the Standard Model background, and a data based approach to determine the dominant ttbar background process. The goal of this search is to determine whether we see an excess of events in our data and set limits on the cross section of the VLL pair production.
- Host: Tulika Bose
- Preliminary Exam
- Investigation of oxide defects and heterostructure modifications for use in quantum computing
- Time: 3:30 pm - 5:30 pm
- Place: B343 Sterling
- Speaker: Emily Joseph, Physics PhD Graduate Student
- Abstract: Si/SiGe quantum dots are attractive candidates for quantum computation yet there are significant challenges to overcome in an effort to improve the scalability of the system. These devices are susceptible to charge noise, some of which may arise from two-level systems (TLS) in the oxide. In this work we use resonator measurement and STEM images to investigate ALD oxide quality to improve semiconducting qubits. Another challenge inherent to Si/SiGe quantum dots is the energy splitting of the conduction band valley states. The valley splitting in Si devices is largely variable and unpredictable and it would be advantageous to be able to predictably rely on a designed-in valley splitting. A modification to the heterostructure has been produced with oscillating concentration of Ge through the quantum well, called the Wiggle Well. Theory predicts that this structure will show strong spin-orbit coupling and with shear strain can have a deterministically large valley splitting. Here we describe methods for mechanically introducing shear strain into the quantum well and a proposed experiment measuring the spin-orbit coupling of the Wiggle Well and making a Loss-DiVincenzo qubit without a micromagnet.
- Host: Mark Eriksson
Thursday, December 14th, 2023
- Academic Calendar
- Study day
- Abstract: *Note: actual end time may vary.* URL:
- Climate & Diversity
- Climate & Diversity Committee all-department coffee hour
- Time: 2:00 pm - 3:00 pm
- Place: Chamberlin Hall, 2nd floor lobby
- Speaker: Various, UW–Madison physics
- Abstract: The Climate and Diversity Committee invites members of the department to attend an informal coffee hour. We hope to engage in conversation about different aspects of the work of the committee and get feedback from the community about future initiatives. We hope you’ll stop by for coffee and cookie from Bloom (!) and to share your thoughts. Many thanks to Sarah Perdue, Rachel Zizmann, Katerina Moloni, Bindesh Tripathi and Sharon Kahn for organizing this; I look forward to seeing many of you there! Thanks and best regards, Tulika Bose (for the Climate & Diversity committee)
- Host: Climate and Diversity Committee
- Wisconsin Quantum Institute Seminar
- Under the hood: microscopic noise characterization in semiconductor quantum dots
- Time: 3:30 pm - 5:00 pm
- Place: Discovery Building, DeLuca Forum
- Speaker: John Nichol, University of Rochester
- Abstract:
Electron spins in silicon quantum dots are excellent qubits due to their long coherence times, scalability, and compatibility with advanced semiconductor technology. Even though single- and two-qubit gates with fidelities above 99% have been achieved in Si spin qubits, charge noise in the semiconductor environment still hinders gate fidelities. Despite the importance of charge noise, key questions like what specific defects cause the noise, where they are in the device, and how they are thermalized, remain unanswered. I will discuss recent work probing individual two-level fluctuators (TLFs) in Si/SiGe quantum dots via simple transport measurements. We find that the TLFs depend sensitively on gate voltage and temperature. We also find that the TLFs are likely not described by a model involving isolated dipole fluctuators coupled to a phonon bath, and that current through the quantum dot appears to heat the TLFs. These measurements open up new pathways for detailed characterization of noise sources in spin qubits.
This event starts at 3:30pm with refreshments, followed at 3:45pm by a short presentation by Ben Harpt (PhD student Mark Eriksson group) titled "Longitudinal electron-photon coupling in a quantum-dot qubit: expanding the toolbox for quantum engineers". The invited presentation starts at 4pm.
- Host: Mark Eriksson
Friday, December 15th, 2023
- Academic Calendar
- Exams
- Abstract: *Note: actual end time may vary.* URL:
Saturday, December 16th, 2023
- Academic Calendar
- Exams
- Abstract: *Note: actual end time may vary.* URL:
Sunday, December 17th, 2023
- Academic Calendar
- Commencement
- Time: 10:00 am - 11:00 am
- Abstract: URL: