Research, teaching and outreach in Physics at UW–Madison
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Physics & math senior Gage Siebert awarded NSF GRFP
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Gage Siebert
Congratulations to Gage Siebert for being awarded a National Science Foundation Graduate Research Fellowship! Gage is a senior math and physics major who has been conducting research in radio astronomy and cosmology. He is working on the optics of NASA’s EXCLAIM mission and constructing a periodicity search using the Tianlai Radio Array. Gage is also a 2021 Hilldale Fellow and Goldwater Scholar, and has won the department’s Hagengruber Scholarship, Liebenberg Family Scholarship, and Henry & Eleanor Firminhac Scholarship. He plans to attend graduate school but has not decided where yet.
Peter Timbie, Gage’s research advisor, says:
Congratulations Gage on winning one of these exceedingly rare awards! We’re really proud of you,Best of luck with you proposal to search for periodic signals in cosmological survey data and your plans for graduate school.
21 UW–Madison students in total received the fellowship, a highly sought and competitive award. The Graduate Research Fellowship Program supports high-potential scientists and engineers in the early stages of their careers. Each year, more than 12,000 applicants compete for 2,000 fellowship awards.
Awardees from UW–Madison, including both undergraduate and graduate students, represent a variety of specializations across science, engineering, and technology. Another 23 UW–Madison students were recognized with honorable mentions.
The program provides awardees with three years of financial support consisting of a $34,000 annual stipend and a $12,000 education allowance. UW–Madison contributes toward fringe benefits.
Fringe benefits: new technique makes x-rays more laser-like
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Detecting a chemical change is often easy: colors may change, heat may be released, or something may smell different. Seeing reactions at the molecular level is not quite so easy, but knowing exactly when and how chemical bonds form or atoms move around is crucial to understanding chemical processes.
X-ray pulses allow researchers to create real-time movies of chemical reactions at the molecular scale (click on image to see animation)
In a new study published March 15 in Proceedings of the National Academy of Sciences, University of Wisconsin–Madison physics professor Uwe Bergmann and his collaborators have turned ultrafast x-ray pulses into something more akin to an optical laser, with cleaner, directional pulses. Their work may lead to visualizing chemical reactions faster than ever at the atomic scale.
“This work is the first step to do with x-rays the same kind of [techniques] which you do with regular lasers,” says Bergmann, the study’s senior author. “We have opened a time window for looking at chemical processes with attosecond [one billionth of one billionth of a second] precision. It’s a new frontier.”
Uwe Bergmann
Around a decade ago, researchers began using powerful x-ray free-electron lasers, which allow them to make ultrafast movies of molecular changes in real time on the femtosecond scale (one thousand times slower than an attosecond). Compared to visible lasers, which provide clean, single-wavelength beams of light, x-ray lasers are somewhat dirty: they contain multiple wavelengths of light of randomly varying intensity.
“What all scientists have done, and are still doing, is that you just adapt to what you get and then you design your experiments around them,” Bergmann says. “That also means that certain experiments, which in the optical laser regime are now standard, have not been possible.”
Bergmann and his colleagues somewhat accidentally discovered a way to make x-rays more like an optical laser. In their experimental setup, they shine intense but dirty x-ray pulses at a manganese sample. When these pulses hit a manganese atom, a lower-level electron is ejected and the hole it leaves is rapidly filled by a higher-level electron. The energy difference is emitted as a photon of a characteristic color. Very intense pulses can create enough of these holes. An emitted photon can effectively stimulate the emission of another one, leading to an avalanche of stimulated X-ray emission, mostly in the forward direction towards their detector.
Every so often, the detector that captures these stimulated emissions showed something they were not expecting: strong fringes, the characteristic pattern that results from constructively and destructively interfering signals. The fringes suggested that they had observed two x-ray emission pulses, separated by only a few femtoseconds.
“We were confused,” Bergmann says. “How did such a pair of x-ray pulses come about?”
After many discussions, calculations, and simulations, the team ruled out many possible explanations, until they finally realized what had happened: occasionally, two of the many spikes in the dirty pulses were much stronger than the rest of them. When these strong spikes occurred a few femtoseconds apart, and each had enough intensity, a clean pair of stimulated x-ray emission pulses emerged.
Two strong x-ray pulses hit the manganese sample, are stretched through the monochromator, and overlap, leading to the characteristic fringes.
Before these two pulses reach the detector, they first travel through a monochromator — essentially a prism that stretches light, much like how white light passing through a clear prism is stretched into a rainbow. These stretched pulses then overlap timewise, and those frequencies that are in phase with each other can add up to become more intense or cancel each other out into dark troughs. Hence, the fringes.
“At times, each signal is rather clean and of similar strength, and one obtains very strong interference fringes,” Bergmann says. “We know that the fringe spacings are directly related to the time difference of the two pulses, and because we can measure them very precisely, we can obtain their time difference with extreme, attosecond precision.”
Currently, these pulse pairs are generated very rarely, Bergmann and his collaborators will work with the accelerator scientists to find ways to manipulate the ‘dirty’ pulses and enhance the chance of producing the pairs. They are optimistic that their work opens the door to new applications of such x-ray pulse pairs — the types of techniques that are used commonly with visible laser light.
“We’re trying to move nonlinear laser optics into the x-ray regime,” Bergmann says. “In the x-ray regime, you can probe certain phenomena that you just cannot optically access. X-ray wavelengths are comparable to the distances between atoms, and we can knock out lower-level electrons to get element specificity with them.”
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Bergmann’s contribution to this research was funded in part by the U.S. Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory (DE-AC02-76SF00515). Other authors were supported by various funding as described in the study.
Massive bubbles at center of Milky Way caused by supermassive black hole
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The enormous clouds of material known as the eRosita and Fermi bubbles extend above and below the galactic plane of the Milky Way. NASA/KAREN YANG/MATEUSZ RUSZKOWSKI/ELLEN ZWEIBEL
New research reveals the origins of enormous bubbles of material emanating from the center of the Milky Way.
The related structures — known as the eRosita and Fermi bubbles and the microwave haze — are the result of a powerful jet of activity from the supermassive black hole at the center of the galaxy. The study, published March 7 in Nature Astronomy, also shows the jet began spewing out material about 2.6 million years ago, and lasted about 100,000 years.
Ellen Zweibel
The work was led by Karen Yang of National Tsing Hua University in Taiwan with University of Wisconsin–Madison astronomer Ellen Zweibel and Mateusz Ruszkowski at the University of Michigan.
The black hole origin of these huge bubbles rules out an alternative model that the expansion of the material was driven by exploding stars. Such a nuclear starburst would last about 10 million years, according to Zweibel, a professor of astronomy and physics at UW–Madison.
“On the other hand, our active black hole model accurately predicts the relative sizes of the eRosita X-ray bubbles and the Fermi gamma ray bubbles, provided the energy injection time is about one percent of that, or one-tenth of a million years,” Zweibel says. “Injecting energy over 10 million years would produce bubbles with a completely different appearance. While both the black hole and stellar explosion models were in reasonably good agreement with the gamma ray data, it’s the discovery of the X-ray bubbles, and the opportunity to compare the X-ray and gamma ray bubbles, which provide the crucial, previously missing piece.”
The enormous structures are nearly 36,000 light-years tall, one-third the diameter of the Milky Way. The eRostia and Fermi bubbles were named for the telescopes that discovered them in 2020 and 2010, respectively.
Sridhara Dasu named a member of the International Committee on Future Accelerators
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High energy physicist Sridhara Dasu was recently named a member of the International Committee for Future Accelerators (ICFA), a term he’ll serve for three years. ICFA was created to facilitate international collaboration in the construction and use of accelerators for high energy physics. The Committee has 16 members, selected primarily from the regions most deeply involved in high-energy physics. Dasu will be representing the United States on the committee.
Blending the rules: how physics helps paint a new picture for artists of all mediums
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This post was written by Rachael Lee, a student science writer with University Communications.
A singer or a violinist’s performance produces sound waves that echo across a concert hall. A painter may mix different paint colors to create a new hue. Dancers use forces like gravity and inertia to produce stunning displays.
At first glance, the arts and physical sciences may look like very separate disciplines. However, many art forms are based on physics.
One hugely popular physics course at the University of Wisconsin–Madison shows how the arts and physics are, in fact, inextricably linked. Physics in the Arts (Physics 109) examines sound and light using examples from the arts. Physics in the Arts has been taught at UW–Madison since 1969, when it was started by physics professors Willy Haeberli and Ugo Camerini. Today’s instructors, professors Pupa Gilbert and A. Baha Balantekin, are continuing and extending the class’s mission to bridge the two disciplines to benefit both physicists and artists in understanding and appreciating each other’s fields.
Balantekin says that the interdisciplinary course shows the rest of the campus community that physics is not just a technical subject. By demonstrating physics in a medium familiar to artists, it helps provide a new perspective and appreciation for the sciences. “If you’re a musician, it’s much better to learn about the physics behind how your instrument works, or the physics behind how colors mix. It’s more interesting, and then it still helps them to learn,” he says.
Design and performance of the prototype Schwarzschild-Couder telescope camera
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The debut of a new detector has many “firsts”: the first assembly, the first shift, the first light, the first detection… But if there’s one thing that makes a debut official—sort of like a detector’s birth certificate—it’s the detailed description of how the detector was built and how it performs.
And this is achieved in a new paper by members of the Cherenkov Telescope Array Consortium, published in the Journal of Astronomical Telescopes, Instruments and Systems. The paper documents the design of the camera of the prototype Schwarzschild-Couder Telescope (pSCT), a medium-sized candidate telescope for the Cherenkov Telescope Array (CTA). The paper also includes performance metrics that show its potential as a very-high-energy gamma-ray detector and that have already been used to plan an upgrade, a project which is now well underway. Very high energy gamma rays are the highest energy photons in the universe and can unveil the physics of extreme objects, including black holes and possibly dark matter.
The pSCT uses novel dual-mirror optics, rather than more traditional single-mirror optics, and relies on high-speed electronics to cover CTA’s middle energy range from 80 GeV to 50TeV. This camera was developed by a team spanning multiple universities and co-led by UW–Madison physics professor Justin Vandenbroucke, who has been working on this project since 2009.
Theoretical physicist Bernice Durand was a leader of gender equity on campus and in her field
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Bernice Durand
Bernice Durand, Professor Emerita and one of the first two female professors in the UW–Madison Department of Physics, passed away February 7.
Durand was a theoretical physicist who specialized in particle theory and mathematical physics. Her research was on symmetry relations in algebra and physics, plus the phenomenology of high-energy interactions at large particle accelerators. She earned her BS and PhD degrees in physics from Iowa State University. In 1970, she started at UW–Madison as a research associate and lecturer and joined the faculty in 1977, where she directed nine PhD and three MS students.
As the first Associate Vice Chancellor for Diversity & Climate, Professor Durand provided leadership to ensure that faculty, staff, and student diversity issues including race, ethnicity, gender, sexual preference, and classroom and general campus workplace climate issues be addressed, and that search committees for non-classified staff be trained in broadening the pool of applicants and eliminating implicit bias. Durand co-directed a grant from the Alfred P. Sloan Foundation to the UW System designed to create more equity, flexibility and career options for faculty and academic staff. She was also a member of the leadership team of the Women in Science and Engineering Leadership Institute sponsored by the National Science Foundation to increase the participation and status of women in science.
A recipient of the Chancellor’s Award for Outstanding Teaching, Professor Durand taught courses at all levels, from modern physics for non-scientists (“Physics for Poets”) to a specialized course she developed for advanced graduate students in the use of topology and algebra in quantum field theory. In the mid-1990s, she used technological and pedagogical techniques in her teaching, such as broadcasting her modern physics for non-scientists course on public television with web-based coursework and pioneering one of two early versions of MOOCs (massive open online courses) on campus.
The department announced the annual Bernice Durand Undergraduate Research Scholarship in 2003, which gives preference to students from underrepresented groups in Physics and Astronomy who show research potential, motivation, and interest in the discipline. In 2018, the department’s Board of Visitors sought to create an endowed faculty fund in honor of Durand. Thanks to generous support from several Board of Visitors members and Bernice’s husband, Professor Emeritus Randy Durand, the Bernice Durand Faculty Fellowship was established in 2021. The Department plans to use the Durand Faculty Fellowship to support a professor in the department who will expand efforts to create a more diversified faculty.
Bernice is survived by her husband, Loyal Durand, also a UW–Madison Professor Emeritus of Physics; by stepsons Travis, Tim, and Chris Durand, whom she helped to raise from early ages; and by five nieces and nephews.
Their instrument, known as an optical lattice atomic clock, can measure differences in time to a precision equivalent to losing just one second every 300 billion years and is the first example of a “multiplexed” optical clock, where six separate clocks can exist in the same environment. Its design allows the team to test ways to search for gravitational waves, attempt to detect dark matter, and discover new physics with clocks.
From one sphere of supercooled strontium atoms, Kolkowitz’s group multiplexes them into six separate spheres, each of which can be used as an atomic clock.
“Optical lattice clocks are already the best clocks in the world, and here we get this level of performance that no one has seen before,” says Shimon Kolkowitz, a UW–Madison physics professor and senior author of the study. “We’re working to both improve their performance and to develop emerging applications that are enabled by this improved performance.”
Atomic clocks are so precise because they take advantage of a fundamental property of atoms: when an electron changes energy levels, it absorbs or emits light with a frequency that is identical for all atoms of a particular element. Optical atomic clocks keep time by using a laser that is tuned to precisely match this frequency, and they require some of the world’s most sophisticated lasers to keep accurate time.
By comparison, Kolkowitz’s group has “a relatively lousy laser,” he says, so they knew that any clock they built would not be the most accurate or precise on its own. But they also knew that many downstream applications of optical clocks will require portable, commercially available lasers like theirs. Designing a clock that could use average lasers would be a boon.
Shimon Kolkowitz one of four UW professors awarded Sloan Fellowship
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Four University of Wisconsin–Madison professors, including assistant professor of physics Shimon Kolkowitz, have been named to Sloan Research Fellowships — competitive, prestigious awards given to promising researchers in the early stages of their careers.
“Today’s Sloan Research Fellows represent the scientific leaders of tomorrow,” says Adam F. Falk, president of the Alfred P. Sloan Foundation, which has awarded the fellowships since 1955. “As formidable young scholars, they are already shaping the research agenda within their respective fields—and their trailblazing won’t end here.”
Kolkowitz, an assistant professor of physics, builds some of the most precise clocks in the world by trapping ultracold atoms of strontium — clocks so accurate they could be used to test fundamental theories of physics and search for dark matter.
UW–Madison’s other 2022 Sloan Fellows are Tatyana Shcherbina (math), Zachary K. Wickens (chemistry) and Andrew Zimmer (math).
The UW–Madison professors are among 118 researchers from the United States and Canada honored by the New York-based philanthropic foundation. The four new fellows join 110 UW–Madison researchers honored in the past.
Each fellow receives $75,000 in research funding from the foundation, which awards Sloan Research Fellowships in eight scientific and technical fields: chemistry, computer science, economics, mathematics, computational and evolutionary molecular biology, neuroscience, ocean sciences and physics.
Physics of Climate Change project funded by WI Idea grant
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Eleven research projects that illustrate how the Wisconsin Idea has evolved — including one from the Department of Physics — have now been funded by Extension and the Office of the Vice Chancellor for Research and Graduate Education.
The premise of the Wisconsin Idea, extending university knowledge to all corners of the state, is traditionally described as starting on campus and traveling to other parts of Wisconsin. This new series of grant-funded projects recognizes the value of knowledge transfer in reverse: utilizing Extension’s local networks to bring community perspectives and knowledge into research studies conducted on campus.
The Wisconsin Idea is almost 120 years old, and in that time it has evolved to include the wide range of topics currently being studied by faculty and specialists at UW–Madison. Extension’s locally based educators deliver evidence-based programming for farmers and 4-H youth and also help address specific issues in local communities by sharing expertise on natural resources, family, financial, economic development, and health/well-being topics.
The heart of the Wisconsin Idea – creating vital links between UW–Madison and communities across the state to inform community programming and improve lives – is embodied as the core mission of Extension. The new grant series will showcase how communities can both inform and benefit from university research. This work follows the longstanding tradition of Extension’s role to advance the Wisconsin Idea, while the research methods used to develop knowledge continue to evolve.
Extension collaborated with the Office of the Vice Chancellor for Research and Graduate Education to create the Wisconsin Idea Collaboration Grant project series. The competitive grants will kickstart applied research and development of innovative educational programming or community engagement to address community needs and priorities.
Funded project: The Physics of Climate Change
Principal Investigator Mallory Conlon (Physics); co-PIs Cierra Atkinson (Physics), Haddie McLean (Physics), and Joanna Skluzacek, Professor and STEM Specialist, Division of Extension
The scientific principles explaining and predicting the effects of climate change are being lost in the noise of rampant misinformation. Understanding of climate change varies across age groups and location, and many K-12 teachers are left without the support needed to incorporate climate change concepts in their curricula.
To mitigate misinformation, this project will create hands-on activities to understand the impacts of climate change and empower teachers to accurately share content with their students. Specific efforts will include a museum exhibit at the Ingersoll Physics Museum, outreach demonstration for the Wonders of Physics traveling show, and an activity kit designed to empower middle and high school students, teachers, and general audiences to identify accurate information about climate change.
