Research, teaching and outreach in Physics at UW–Madison
Graduate Students
Justin Edwards earns National Defense Science and Engineering Graduate Fellowship
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Physics PhD and ECE MS student Justin Edwards has been awarded the prestigious National Defense Science and Engineering Graduate Fellowship in the category of Physics (including Optics), with a proposal titled “Multispectral imaging in the near infrared for next-generation analog night vision systems”. Justin is advised by ECE Professor and physics affiliate professor Mikhail Kats and collaborates extensively with ECE PhD students Rabeeya Hamid and Demeng Feng, and the group of Dan Congreve at Stanford University.
MSPQC’s Preetham Tikkireddi wins second place at QED-C student poster presentation
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MSPQC student Preetham Tikkireddi won second place for his poster, “Understanding security side channel attacks on multi-tenancy quantum computers,” at the plenary meeting of the Quantum Economic Development Consortium (QED-C), held March 20-21 in Evanston, IL.
Students who attended the plenary first learned best practices for presenting their research to a non-science audience, a useful skill for a cutting-edge field where investors, hiring managers, and policy makers do not necessarily have a quantum background. Then, the students implemented those skills at the judged poster session.
“[The poster session attendees] are really smart people, but they’re not quantum people, so you set them up for asking questions, and based on the questions that they’re asking, you determine how deep you want to go into your research.” Tikkireddi says. “It was a very different kind of experience, rather than just a plain research presentation to a professor or people who already know the field.”
A total of 17 students presented posters at the first-ever QED-C student program and poster competition. UW–Madison MSPQC student Preetham Tikkireddi (right) was one of three graduate students to win the top honor at the competition. | Photo credit: QED-C
Tikkireddi’s research, conducted with computer sciences professor Swamit Tannu, looked at the potential for exploiting crosstalk when two users access the same quantum computer at the same time.
“Right now, quantum computers are really expensive, and the way we access them is by sending jobs to these quantum providers like IBM or IonQ,” Tikkireddi explains. “But the queues are really long. If you’re lucky, you can get the results back the next day.”
Quantum computing capacity is growing rapidly in the form of more and more qubits, and most jobs submitted to these long queues do not need to use all the qubits. Tikkireddi and Tannu thought that one way to increase throughput would be to allow users to share the same quantum computer, each using a subset of the qubits. But quantum computations rely on qubit entanglement, where physically separate qubits interact and share information. It was unclear if sharing a quantum computer opens users to security risks.
In his work, Tikkireddi asked if he could count C-NOTs — the gate that is used to create this entanglement — of another user. He entangled two qubits, then asked if two other qubits could “hear” what the first two were doing.
“We were able to use that to figure out how many C-NOTs the other guy is doing. That’s step one of an attack,” Tikkireddi says. “Your algorithm is your intellectual property, so you don’t want people to steal it. It’s a security problem.”
With this initial analysis identifying potential security risks amongst shared quantum computer use, Tikkireddi says providers should currently not let users share computing time, and that future research should focus on ways to mitigate these crosstalk attacks in an effort to balance efficiency with safeguarding intellectual property.
Tikkireddi credits Tannu for helping to guide his poster away from a traditional research poster and toward one more accessible to a non-science audience. He also appreciates the support from MSQPC associate director Katerina Moloni for encouraging and preparing students to take advantage of these training opportunities.
“It was a really good networking opportunity, especially for me, who is looking for a job right now,” Tikkireddi says. “I would highly recommend students to go to these kinds of events because we get a chance to interact with people in the industry.”
Cristian Vega awarded Callen Award for Excellence in Theoretical Plasma Physics Research
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Cristian Vega
Congrats to (now) Dr. Cristian Vega who won the Callen Award for Excellence in Theoretical Plasma Physics Research! Vega won the award on April 29, just days before defending his thesis on May 3.
The Callen Award is awarded annually to a UW–Madison plasma physics graduate student for achievements in plasma theory. Now-retired Professor Emeritus Jim Callen was a long-time faculty member in the Nuclear Engineering and Engineering Physics department. Callen was also an affiliate faculty member of the Physics department.
On Saturday, April 13, physics students Will Cerne and William Griffin were among the 168 University of Wisconsin–Madison Letters & Science undergraduates inducted to the Phi Beta Kappa (ΦΒΚ) academic society. The induction ceremony was held at Varsity Hall in Union South with 350 attending.
In addition to the induction of new undergraduate members, the ceremony also honored four individuals for their contributions to UW–Madison, including Jimena González, a member of the UW–Madison chapter of the Edward A. Bouchet Society and a PhD candidate in Physics (observational cosmology). González accepted one of ΦΒΚ’s graduate student induction invitation.
UW–Madison’s ΦΒΚ chapter, founded in 1899, seeks to honor students who rigorously explore the sciences, arts and humanities.
L&S Dean Eric M. Wilcots led the opening procession and welcome. Chapter President David W. Johnson, economics, hosted the celebration’s 125th year of the founding of the UW–Madison chapter of Phi Beta Kappa. Special guest and president of the national Phi Beta Kappa Society Peter Quimby PhD’99 presented the history of ΦΒΚ. ΦΒΚ stands for philosophia biou kubernetes, which translates to “the love of wisdom is the helmsman of life.”
Inductees excel in all areas of study, ranging from physics to anthropology, and they must have a cumulative GPA of 3.80 or above and meet strenuous math, language, and breadth requirements.
A committee of faculty and staff review the student record for nomination into the chapter. Inductees have a love for learning in multiple areas of study at the intermediate and advanced levels, exploring far beyond their major area of study at UW–Madison.
Three physics students earn 2024 NSF GRFP awards, four students earn honorable mention
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Congrats to Physics PhD student Joyce Lin and undergraduates Brooke Kotten and Lucy Steffes on being awarded the 2024 NSF GRFP! PhD students Owen Eskandari, Sam Kramer, Tali Oh, and Julia Sheffler were awarded Honorable Mentions.
The National Science Foundation (NSF) recently announced the 2024 awards in its Graduate Research Fellowship Program (GRFP), a prestigious and competitive fellowship that helps support outstanding graduate research across the country.
Of those offered awards, 19 are currently UW–Madison graduate students. Seven current UW–Madison undergraduates were also offered the award for their graduate study. Additionally, 33 UW–Madison students were recognized with honorable mentions from NSF.
UW–Madison strongly encourages senior undergraduates and early-career graduate students to apply to this fellowship.
The largest magnetic fields in galaxy clusters have been revealed for the first time
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By Alex Lazarian, Yue Hu, and Ka Wai Ho
Galaxy clusters, immense assemblies of galaxies, gas, and elusive dark matter, form the cornerstone of our Universe’s grandest structure — the cosmic web. These clusters are not just gravitational anchors, but dynamic realms profoundly influenced by magnetism. The magnetic fields within these clusters are pivotal, shaping the evolution of these cosmic giants. They orchestrate the flow of matter and energy, directing accretion and thermal flows, and are vital in accelerating and confining high-energy charged particles/cosmic rays.
However, mapping the magnetic fields on the scale of galaxy clusters posed a formidable challenge. The vast distances and complex interactions with magnetized and turbulent plasmas diminish the polarization signal, a traditionally used informant of magnetic fields. Here, the groundbreaking technique — synchrotron intensity gradients (SIG) — developed by a team of UW–Madison astronomers and physicists led by astronomy professor Alexandre Lazarian, marks a turning point. They shifted the focus from polarization to the spatial variations in synchrotron intensity. This innovative approach peels back layers of cosmic mystery, offering a new way to observe and comprehend the all-important magnetic tapestry on scale of millions of light years.
A landmark study published in Nature Communications has employed the SIG technique to unveil the enigmatic magnetic fields within five colossal galaxy clusters, including the monumental El Gordo cluster, observed with the Very Large Array (VLA) and MeerKAT telescope. This colossal cluster, formed 6.5 billion years ago, represents a significant portion of cosmic history, dating back to nearly half the current age of the universe. The findings in El Gordo, characterized by the largest magnetic fields observed, provide crucial insights into the structure and evolution of galaxy clusters.
Left: Image of the El Gordo cluster observed Chandra X-ray Observatory and ground-based optical telescopes (credits: NASA/ESA/CSA). Magnetic field visualized by streamlines are superimposed on the image. Right: images of the Fishhook galaxy (top) and Milky Way (bottom).
The research is a fruitful collaboration between the UW–Madison team and their Italian colleagues, including Gianfranco Brunetti, Annalisa Bonafede, and Chiara Stuardi from the Instituto do Radioastronomia (Bologna, Italy) and the University of Bologna. Brunetti, a renowned expert in the high-energy physics of galaxy clusters, is enthusiastic about the potential that the SIG technique holds for exploring magnetic field structures on even larger scales, such as the Megahalos recently discovered by him and his colleagues.
Echoing this excitement is the study’s lead researcher, physics graduate student Yue Hu.
“This research marks a significant milestone in astrophysics,” Hu says. “Utilizing the SIG method, we’ve observed and begun to comprehend the nature of magnetic fields in galaxy clusters for the first time. This breakthrough heralds new possibilities in our quest to unravel the mysteries of the universe.”
This study lays the groundwork for future explorations. With the SIG method’s proven effectiveness, scientists are optimistic about its application to even larger cosmic structures that have been detected recently with the Square Kilometre Array (SKA), promising deeper insights into the mysteries of the Universe magnetism and its effects on the evolution of the Universe Large Scale Structure.
UW physicists part of study offering unique insights into the expansion of the universe
In the culmination of a decade’s worth of effort, the Dark Energy Survey collaboration of scientists analyzed an unprecedented sample of nearly 1,500 supernovae classified using machine learning. They placed the strongest constraints on the expansion of the universe ever obtained with the DES supernova survey. While consistent with the current standard cosmological model, the results do not rule out a more complex theory that the density of dark energy in the universe could have varied over time.
An example of a supernova discovered by the Dark Energy Survey within the field covered by one of the individual detectors in the Dark Energy Camera. The supernova exploded in a spiral galaxy with redshift = 0.04528, which corresponds to a light-travel time of about 0.6 billion years. This is one of the nearest supernovae in the sample. In the inset, the supernova is a small dot at the upper-right of the bright galaxy center. Image: DES collaboration
DES scientists presented the results January 8 at the 243rd meeting of the American Astronomical Society and have submitted them for publication to the Astrophysical Journal.
Keith Bechtol
The work is the output of over 400 DES scientists, including UW–Madison physics professor Keith Bechtol and former graduate student Robert Morgan, PhD ’22.
In 1998, astrophysicists discovered that the universe is expanding at an accelerating rate, attributed to a mysterious entity called dark energy that makes up about 70% of our universe. While foreshadowed by earlier measurements, the discovery was somewhat of a surprise; at the time, astrophysicists agreed that the universe’s expansion should be slowing down because of gravity.
This revolutionary discovery, which astrophysicists achieved with observations of specific kinds of exploding stars, called type Ia (read “type one-A”) supernovae, was recognized with the Nobel Prize in Physics in 2011.
In this new study, DES scientists performed analyses with four different techniques, including the supernova technique used in 1998, to understand the nature of dark energy and to measure the expansion rate of the universe.
As a graduate student in Bechtol’s group, Morgan was part of the DES supernova working group that worked to identify type Ia supernova. This group had to address two main concerns with the data to enhance detection fidelity.
“One is that there is some leakage of other types of supernovae into the sample, so you have to calibrate the rate of misclassification,” Bechtol explains. “Also, the brightness of the supernova gives us a way of estimating its distance, but there is a distribution of how bright the Ia supernovae are. Because we are slightly less likely to detect the intrinsically fainter supernovae, there is a small bias that needs to be accounted for.”
Bechtol has been part of the DES collaboration since its formation in 2012, serving as a co-convener of the DES’s Science Release Working Group for four years and a co-convener of the Milky Way Working Group for two years. His role in this new study was in data processing and presentation.
“We collect all of the data, process it, and then release it as a coherent set of data products, both for use by the DES collaboration and as part of public releases to the community,” Bechtol says. “One of the aspects I worked on is the photometric calibration — our ability to measure the fluxes of objects accurately and precisely. It’s an important part of the supernova analysis and something that I’ve been working on continuously over the past ten years.”
Physics PhD student Stephen McKay named ALMA ambassador
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Stephen McKay
Congrats to physics graduate student Stephen McKay on being named an ALMA ambassador!
ALMA, or the Atacama Large Millimeter/submillimeter Array, is the largest radio telescope in the world. It can detect light radiated by clouds of dust grains in some of the earliest and most distant galaxies in the Universe. Researchers can submit proposals to ALMA that direct data collection to observe astronomical targets at a wide range of wavelengths, in order to accomplish many cutting-edge science goals. However, ALMA receives many more proposals than there is time to operate the telescope.
That’s where McKay’s ambassadorship comes in.
“Lots of groups at UW–Madison and other places will propose to get data from these telescope arrays,” McKay says. “In February, I’ll attend a training (through the ambassador program) where they will teach me tips and tricks for writing proposals. Then in early spring, I’ll run a proposal workshop here for anyone who wants to learn how to strengthen a proposal.”
In the Chajnantor Plateau, amazing picture of the antennas under the Milkyway. Credit: Sergio Otarola- ALMA (ESO/NAOJ/NRAO)
McKay is no stranger to proposing and using ALMA data. A third-year graduate student in astronomy professor Amy Barger’s research group, he expects nearly all his publications will be based on ALMA data. His research focuses on old, distant galaxies and measuring and inferring physical properties about them: How massive are they? What is their rate of star formation? What processes trigger the rapid star-formation in these systems?
“The galaxies that I mainly study are faint or hard to detect in optical wavelengths or even near-infrared wavelengths. Until about maybe 25 years ago, we didn’t know a lot of these galaxies existed because they just weren’t visible in the typical telescope images we had,” McKay says. “The portion of the observed electromagnetic spectrum where these galaxies are brightest ranges from 500 microns to nearly one millimeter, which overlaps heavily with ALMA’s spectral coverage.”
Two years ago, McKay attended an ALMA workshop to learn more about how ALMA and similar radio arrays operate. With this ALMA ambassadorship, he will now help run the workshops and offer advice on crafting stronger proposals. The ALMA Ambassador Program is run through the National Radio Astronomy Observatory’s North American ALMA Science Center (NAASC). It provides training and an up to $10,000 research grant to early-career researchers interested in expanding their ALMA/interferometry expertise and sharing that knowledge with their home institutions.
“This program is helpful for me because I will learn more in terms of how to actually do my own research, but then I can also pass along what I learn with the rest of the astronomical community,” McKay says.
Jimena González joins Bouchet Graduate Honor Society
Five outstanding scholars, including Physics PhD student Jimena González, are joining the UW–Madison chapter of the national Edward Alexander Bouchet Graduate Honor Society this academic year.
Jimena González
The Bouchet Society commemorates the first person of African heritage to earn a PhD in the United States. Edward A. Bouchet earned a PhD in Physics from Yale University in 1876. Since then, the Bouchet Society has continued to uphold Dr. Bouchet’s legacy.
“The 2024 Bouchet inductees are making key contributions in their disciplines, as well as to the research, education, and outreach missions of our campus. They truly embody the Wisconsin Idea and are exemplary in every way,” said Abbey Thompson, assistant dean for diversity, inclusion, and funding in the Graduate School.
The Bouchet Society serves as a network for scholars that uphold the same personal and academic excellence that Dr. Bouchet demonstrated. Inductees to the UW–Madison Chapter of the Bouchet Society also join a national network with 20 chapters across the U.S. and are invited to present their work at the Bouchet Annual Conference at Yale University, where the scholars further create connections and community within the national Bouchet Society.
The UW–Madison Division of Diversity, Equity, and Educational Achievement supports each inductee with a professional development grant.
González is a physics PhD candidate specializing in observational cosmology. Her research centers on searching and characterizing strong gravitational lenses in the Dark Energy Survey. These rare astronomical systems can appear as long curved arcs of light surrounding a galaxy. Strong gravitational lenses offer a unique probe for studying dark energy, the driving force behind the universe’s accelerating expansion and, consequently, a pivotal factor in determining its ultimate fate.
During her graduate program, Jimena has received the Albert R. Erwin, Jr. & Casey Durandet Award and the Firminhac Fellowship from the Department of Physics. Additionally, she was honored with the 2023 Open Science Grid David Swanson Award for her outstanding implementation of High-Throughput Computing to advance her research. Jimena has contributed as a co-author to multiple publications within the field of strong gravitational lensing and has presented her work at various conferences. In addition to her academic achievements, Jimena has actively engaged in outreach programs. Notably, she was selected as a finalist at the 2021 UW–Madison Three Minute Thesis Competition and secured a winning entry in the 2023 Cool Science Image Contest. Her commitment to science communication extends to a contribution in a Cosmology chapter in the book AI for Physics. Jimena has also led a citizen science project that invites individuals from all around the world to inspect astronomical images to identify strong gravitational lenses. Jimena obtained her bachelor’s degree in physics at the Universidad de los Andes, where she was awarded the “Quiero Estudiar” scholarship.
“Sandwich” structure found to reduce errors caused by quasiparticles in superconducting qubits
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Qubits are notoriously more prone to error than their classical counterparts. While superconducting quantum computers currently use on the order of 100 to 1000 qubits, an estimated one million qubits will be needed to track and correct errors in a quantum computer designed for real-world applications. At present, it is not known how to scale superconducting qubit circuits to this size.
In a new study published in PRX Quantum, UW–Madison physicists from Robert McDermott’s group developed and tested a new superconducting qubit architecture that is potentially more scalable than the current state of the art. Control of the qubits is achieved via “Single Flux Quantum” (SFQ) pulses that can be generated close to the qubit chip. They found that SFQ-based control fidelity improved ten-fold over their previous versions, providing a promising platform for scaling up the number of qubits in a quantum array.
Robert McDermottVincent Liu
The architecture involves a sandwich of two chips: one chip houses the qubits, while the other contains the SFQ control unit. The new approach suppresses the generation of quasiparticles, which are disruptions in the superconducting ground state that degrade qubit performance.
“This structure physically separates the two units, and quasiparticles on the SFQ chip cannot diffuse to the quantum chip and generate errors,” explains Chuan-Hong Liu, PhD ’23, a former UW–Madison physics graduate student and lead author of the study. “This design is totally new, and it greatly improves our gate fidelities.”
Liu and his colleagues assessed the fidelity of SFQ-based gates through randomized benchmarking. In this approach, the team established operating parameters to maximize the overall fidelity of complex control sequences. For instance, for a qubit that begins in the ground state, they performed long sequences incorporating many gates that should be equivalent to an identity operation; in the end, they measured the fraction of the population remaining in the ground state. A higher measured ground state population indicated higher gate fidelity.
Inevitably, there are residual errors, but the reduced quasiparticle poisoning was expected to lower the error rate and improve gate fidelities — and it did.
The quantum-classical multichip module (MCM). (a) A micrograph of the qubit chip. (b) A micrograph of the SFQ driver chip. (c) A photograph showing the assembled MCM stack; the qubit chip is outlined in red and the SFQ chip is outlined in blue. (d) The circuit diagram for one qubit-SFQ pair. | From Liu et al, PRX Quantum.
“Most of the gates had 99% fidelity,” Liu says. “That’s a one order of magnitude reduction in infidelity compared to the last generation.”
Importantly, they showed the stability of the SFQ-based gates over the course of a six-hour experimental run.
Later in the study, the researchers investigated the source of the remaining errors. They found that the SFQ unit was emitting photons with sufficient energy to create quasiparticles on the qubit chip. With the unique source of the error identified, Liu and his colleagues can develop ways to improve the design.
“We realized this quasiparticle generation is due to spurious antenna coupling between the SFQ units and the qubit units,” Liu says. “This is really interesting because we usually talk about qubits in the range of one to ten gigahertz, but this error is in the 100 to 1000 gigahertz range. This is an area people have never explored, and we provide a straightforward way to make improvements.”
This study is a collaboration between the National Institute of Standards and Technology, Syracuse University, Lawrence Livermore National Laboratory, and UW–Madison.
This work was funded in part by the National Science Foundation (DMR-1747426); the Wisconsin Alumni Research Foundation (WARF) Accelerator; Office of the Director of National Intelligence, Intelligence Advanced Research Projects Activity (IARPA-20001-D2022-2203120004); and the NIST Program on Scalable Superconducting Computing and the National Nuclear Security Administration Advanced Simulation and Computing Beyond Moore’s Law program (LLNL-ABS-795437).
