Events During the Week of November 17th through November 23rd, 2024
Monday, November 18th, 2024
- Thesis Defense
- Quantum Computing with Superconductor-Semiconductor Hybrid Systems
- Time: 10:00 am - 12:00 pm
- Place: B343, Sterling Hall;
- Speaker: Benjamin Harpt, Physics PhD Graduate Student
- Abstract: Quantum computers offer the potential to solve problems beyond the reach of classical computers by harnessing fundamentally different physics. Today, researchers worldwide are racing to develop quantum computers that are both controllable and scalable, utilizing a wide range of hardware approaches to encode quantum information. Superconducting circuits and semiconductor quantum dots are, individually, two of the leading qubit platforms for building solid-state quantum processors; combining the strengths of both materials in hybrid devices opens up new possibilities for quantum computing architectures. This dissertation explores key aspects of superconductor-semiconductor hybrid systems for quantum computing, and is structured in three parts. Part I presents an in-depth overview of silicon quantum-dot qubits, with a focus on experiments investigating crosstalk between exchange-only spin qubits. Part II addresses the integration of these qubits with superconducting resonators for readout and long-range entanglement. Using a quantum-dot device coupled to a vertically integrated resonator, we demonstrate an unconventional electron-photon interaction mechanism and show how it can be utilized for qubit readout and spectroscopy. Finally, Part III examines superconductor-semiconductor hybrid junctions and their qubit applications, detailing the development of superconducting alloys tailored for germanium-based hybrid devices. Together, these findings advance our understanding and introduce new techniques for developing hybrid quantum technologies.
- Host: Mark Eriksson
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Drift-cyclotron loss cone instability in 3D kinetic-ion simulations of WHAM
- Time: 12:05 pm - 1:00 pm
- Place: 1610 Engineering Hall
- Speaker: Aaron Tran, University of Wisconsin-Madison
- Abstract: WHAM's "peak-performance" beam-ion plasma may induce drift-cyclotron loss-cone (DCLC) instability: a coupled ion Bernstein / drift wave excited by the plasma’s radial density gradient and loss-cone velocity distribution. We present 3D plasma simulations, using kinetic ions and isothermal fluid electrons, of various WHAM configurations with sloshing (45 deg. pitch angle) beam-ion distributions from the collisional Fokker-Planck code CQL3D-m as an initial condition. Edge-localized electrostatic waves grow and saturate in ~1–10 μs with ω ~ 1–2× the ion cyclotron frequency. Wave properties can be explained by linear theory of DCLC in a planar slab. DCLC scattering fills the loss cone, so particle confinement is set by axial free streaming (aka "gas dynamic" confinement). Adding cool (~1 keV) ions to the plasma edge improves confinement by ~2–5×. I will also briefly comment on (i) other ways to stabilize DCLC, (ii) how DCLC fits into a broader landscape of instabilities in mirrors, and (iii) the effect of externally-driven shear flows.
Tuesday, November 19th, 2024
- Graduate Program Event
- Virtual Open House for Physics-PhD Applicants
- Time: 10:00 am - 11:00 am
- Place:
- Abstract: Applicants to the UW-Madison Physics PhD program are invited to join faculty, staff and current students for a virtual open house to learn about admissions, PhD program requirements and life in Madison. We'll have plenty of time for Q&A.
- Host: Sharon Kahn
- Climate & Diversity
- Article Discussion: Cultivating Native American scientists: an application of an Indigenous model to an undergraduate research experience
- Time: 12:00 pm - 1:00 pm
- Place: Chamberlin 5310 or over Zoom
- Abstract: The Climate and Diversity Committee is planning to host their regular Current Issues in Physics Discussion Tuesday 11/19/24 at 12pm, in Chamberlin 5310 or over Zoom. This article is an excellent opportunity to discuss equity and supporting Indigenous and Native students during Native American Heritage Month.
- Host: Rachel Zizmann
- Wisconsin Quantum Institute
- Quantum Coffee Hour
- Time: 3:00 pm - 4:00 pm
- Place: Rm.5294, Chamberlin Hall
- Abstract: Please join us for the WQI Quantum Coffee today at 3PM in the Physics Faculty Lounge (Rm.5294 in Chamberlin Hall). This series, which takes place approximately every other Tuesday, aims to foster a casual and collaborative atmosphere where faculty, post-docs, students, and anyone with an interest in quantum information sciences can come together. There will be coffee and treats.
Wednesday, November 20th, 2024
- AI for Science Seminar Series
- AI for the Working Mathematician
- Time: 4:00 pm - 5:30 pm
- Place: Chemistry 1435 (Note Location)
- Speaker: Francois Charton, Meta
- Abstract:
- Host: Gary Shiu
Thursday, November 21st, 2024
- R. G. Herb Condensed Matter Seminar
- Pressure and Strain Control of Multiferroic Order in NiI2
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Shua Sanchez, MIT
- Abstract: Multiferroic materials exhibit a linear coupling between simultaneous magnetic and
ferroelectric orders, a rare and unexpected phenomenon. These intriguing materials have attracted
great interest as a platform for energy-efficient computing by using electric fields to control magnetic
states. The van der Waals material NiI2 has been identified as the first multiferroic material in the 2D
limit. Here, a magnetic spin spiral forms between Ni atoms, which breaks inversion symmetry and
induces a ferroelectric polarization. These electronic orders also break the rotational symmetry of the
lattice, enabling structural tuning parameters to directly couple to them. In this talk, I will discuss
pressure and strain tuning measurements of NiI2 which demonstrate the high degree of tunability of
this system, as characterized by x-ray, Raman, and polarimetry measurements. We observe that
transition temperatures can be strongly enhanced by pressure. Further, strain-tuning is shown to control
the polarization direction of the electronic orders. These results present a path forward for structural
custom tuning of multiferroics to realize the goal of ultrafast state switching. - Host: Victor Brar
- Astronomy Colloquium
- Watch Giant Worlds Form and Grow — A Direct Imaging Perspective
- Time: 3:30 pm - 4:30 pm
- Place: 4421 Sterling Hall
- Speaker: Yifan Zhou, University of Virginia
- Abstract: Recent advances have greatly enhanced our understanding of gas giant planet formation and evolution, with discoveries spanning the onset of formation in protoplanetary disks, direct detections of gas accretion, and constraints on the thermal, dynamical, and atmospheric evolution of gas giants. These findings provide crucial insights into the mechanisms underlying the formation of giant planets and the ways these planets impact the formation environment and the broader planetary systems.
This talk will review key direct imaging observations of young gas giant systems, focusing on the identification of protoplanets, the monitoring of accretion onto young planets, and the empirical constraints of the thermal and angular momentum properties of giant planets. Using the PDS 70 system, the only known planetary systems with two actively accreting planets, as a case study, I will illustrate how time-domain, high-contrast imaging can reveal critical details of gas giant formation. I will also highlight ongoing and upcoming James Webb Space Telescope programs that promise transformative insights into the mass growth and early evolution of giant planets. - Host: Melinda Soares-Furtado
Friday, November 22nd, 2024
- Thesis Defense
- Pulsed-laser calibration of thermal microcalorimeters for X-ray astronomy
- Time: 9:00 am - 11:00 am
- Place: 6242 Chamberlin Hall or
- Speaker: Avirup Roy, Physics PhD Graduate Student
- Abstract: The performance of single photon microcalorimeters for high-resolution X-ray spectroscopy has improved to the point that it can be limited by our ability to calibrate these detectors. X-ray fluorescent lines have been the usual standard for calibrations, but they have intrinsic widths much broader than the current detector resolution. Since microcalorimeters respond to total energy deposited as heat, we have investigated the idea that five hundred 3 eV photons from an ultraviolet laser delivered in a pulse much shorter than the thermal integration time of detectors should look the same as a single 1500 eV X-ray photon. We have illuminated devices that have 290 μm square gold absorbers, superconducting transition-edge sensor (TES) thermometers, and about 1 eV FWHM resolution with ∼ 100 ns pulses from an ultraviolet laser. This produces combs of lines with 3 eV spacing and negligible intrinsic width that can be distinguished to at least 1700 eV. The accuracy of the line energies is limited only by our knowledge of the laser wavelength. Simultaneous illumination with oxygen and aluminum K fluorescent lines shows that the response to an X-ray photon is indistinguishable from the response to a burst of UV photons with the same total energy to better than 0.4 eV at 1500 eV. This performance is more than adequate for our current sounding rocket instrument. We discuss the path forward to possibly demonstrating the 0.1 eV at 10 keV standard that would be desirable for instruments on major space missions.
- Host: Dan McCammon
- Physics Department Colloquium
- The DNA of Particle Scattering
- Time: 3:30 pm - 4:30 pm
- Place: Chamberlin 2241
- Speaker: Lance Dixon, SLAC
- Abstract: At the Large Hadron Collider, the copious scattering of quarks and gluons in quantum chromodynamics (QCD) produces Higgs bosons as well as many backgrounds to searches for new physics. Better theoretical precision in computing Standard Model cross sections is needed to match the improved experimental precision expected with the high-luminosity LHC upgrade. Scattering of quarks and gluons in QCD can be evaluated in perturbation theory and leads to highly intricate, multivariate mathematical functions. To gain further insight into the structure of these functions, one can study a simpler cousin of QCD called planar N=4 SYM. The structural features of these intricate results can be decoded in a way that is analogous to sequencing DNA. Each derivative reads off a letter, like the A,T,G,C letters of the DNA code. Understanding the alphabet, and then reading the code, exposes the physics and mathematics of quantum scattering. Bizarre new symmetries have been unveiled by humans staring at this theoretical data. For example, two scattering amplitudes are secretly related to each other by reading the code backwards. The next hidden symmetries may be revealed by machine learning models "staring at" the data.
- Host: Gary Shiu