Research, teaching and outreach in Physics at UW–Madison
Thad Walker honored with Vilas Distinguished Achievement Professorship
Extraordinary members of the University of Wisconsin–Madison faculty, including physics professor Thad Walker, have been honored during the last year with awards supported by the estate of professor, U.S. senator and UW Regent William F. Vilas (1840-1908).
Walker was one of seventeen professors were named to Vilas Distinguished Achievement Professorships, an award recognizing distinguished scholarship as well as standout efforts in teaching and service. The professorship provides five years of flexible funding — two-thirds of which is provided by the Office of the Provost through the generosity of the Vilas trustees and one-third provided by the school or college whose dean nominated the winner.
In addition, nine professors received Vilas Faculty Mid-Career Investigator Awards and six professors received Vilas Faculty Early Career Investigator Awards.
Detailed analysis of old star provides template for heavy element formation
The fusion furnaces that are the universe’s stars create the elements from helium up to iron. But iron is only number 26 on the periodic table out of well over 100 known elements. So the heavier ones, like gold, lead and uranium, must come from somewhere other than fusion.
Scientists have long known that those heavy elements come from neutron capture, where neutrons are added to an element that make it unstable, then it radioactively decays and its atomic number increases by one. Nearly 70 years ago, they confirmed one site, or event, of a neutron capture method known as the slow, or s-process. The rapid, or r-process, was not confirmed with a site until 2017, when the LIGO/VIRGO collaboration detected a neutron star merger.
“With a neutron star merger, the neutron stars are ripped apart and they throw out neutrons, and you can build lots of heavy elements out of these neutron stars,” says Jim Lawler, a professor of physics at the University of Wisconsin–Madison. “The mystery arises when we look at the total r-process inventory of our home galaxy: Can we explain all that with neutron star mergers or are there additional sites?”
In a new study led by astronomers from the University of Michigan, Lawler and colleagues identified the elemental composition of HD 222925, a Milky Way star located over 1400 lightyears from earth. Their analysis confirmed that the star was rich in r-process elements, and they were able to identify and calculate the relative abundance of each element. They also found that the star is iron- and metal-poor, a proxy for age that indicates HD 222925 is relatively old and provides information about early star formation.
“We were able to determine a complete r-process abundance pattern for what we think is probably one event that happened early in the beginning of the universe,” Lawler says. “So that r-process template now can be used to screen various models of the nuclear physics that produce the r-process and see if the models for all sites are physically correct.”
At UW–Madison, Lawler and scientist Elizabeth Denhartog contributed the spectroscopic analysis that identified the elements in the star. Every element has a unique electromagnetic spectrum that can be separated into spectral lines using a diffraction grating — just like a prism separates white light into a rainbow. HD 222925 is a relatively bright star, meaning it provided stronger spectra to analyze. It was also identified by the Hubble Space Telescope, providing access to data in the ultraviolet range that is normally blocked by the ozone layer and undetectable by telescopes on Earth.
THIS STUDY WAS SUPPORTED IN PART BY NASA (GRANTS GO-15657, GO-15951, AND 80NSSC21K0627); U.S. NATIONAL SCIENCE FOUNDATION (NSF, GRANTS PHY 14-30152, OISE 1927130, AST 1716251 AND AST 1815403); AND THE U.S. DEPARTMENT OF ENERGY (GRANT DE-FG02-95-ER40934); AND NOIRLAB, WHICH IS MANAGED UNDER A COOPERATIVE AGREEMENT WITH THE NSF.
Thirty-two members of the University of Wisconsin–Madison faculty — including physics professor Mark Saffman — have been awarded fellowships from the Office of the Vice Chancellor for Research and Graduate Education for 2022-23. The awardees span the four divisions on campus: arts and humanities, physical sciences, social sciences and biological sciences.
“These awards provide an opportunity for campus to recognize our outstanding faculty,” says Steve Ackerman, vice chancellor for research and graduate education. “They highlight faculty efforts to support the research, teaching, outreach and public service missions of the university.”
The awards are possible due to the research efforts of UW–Madison faculty and staff. Technology that arises from these efforts is licensed by the Wisconsin Alumni Research Foundation and the income from successful licenses is returned to the OVCRGE, where it’s used to fund research activities and awards throughout the divisions on campus.
Mark Saffman was awarded a WARF professorship. These professorships come with $100,000 and honor faculty who have made major contributions to the advancement of knowledge, primarily through their research endeavors, but also as a result of their teaching and service activities. Award recipients choose the names associated with their professorships. Saffman, the Johannes Rydberg Professor of Physics and director of The Wisconsin Quantum Institute, first began work on atomic physics and initiated a long-term effort to develop quantum computers. He is known for his research as a leader in the ongoing development of atomic quantum computers based on the Rydberg blockade mechanism.
In addition, physics affiliate professor Mikhail Kats received a Romnes Faculty Fellowship.
Congratulations to Professor Lawler on his retirement!
After 42 years on the UW–Madison faculty, Jim Lawler, the Arthur and Aurelia Schawlow Professor of Physics, has announced his retirement. Lawler is an atomic, molecular & optical physicist with a focus developing and applying laser spectroscopic techniques for determining accurate absolute atomic transition probabilities. His retirement is official as of May 22.
“What we’ve really done gradually over four-plus decades is make atomic spectroscopy more quantitative so that people can use it to really learn the detailed physics and chemistry of the remote universe,” Lawler says.
Lawler received his MS (’74) and PhD (’78) from this department, studying with now-professor emeritus Wilmer Anderson. In the two years after earning his doctorate, he was a research associate at Stanford University, and returned to UW–Madison as an assistant professor in 1980.
“There was a little bit of a disadvantage to come back to a place where I had recently been as a student,” Lawler says. “But I knew I would get extremely good graduate students and I would have access to a lot of infrastructure, and that combination really drew me back.”
He had extremely good graduate students and postdocs. Lawler supervised 26 PhD students and 10 terminal MS students. Those students and postdocs have gone on to prestigious National Research Council Fellowships, group lead positions at major companies, and tenured professorships, amongst many others.
Lawler served as department chair from 1994-1997. He also accumulated numerous awards and honors over his distinguished career. He is a fellow of the American Physical Society, the Optical Society of America, the U.K. Institute of Physics, and in 2020 he was elected a Legacy Fellow of the inaugural class of American Astronomical Society Fellows. He won the 1992 W. P. Allis Prize of the American Physical Society and the 1995 Penning Award from the International Union of Pure and Applied Physics for research in plasma physics, the two highest National and International Awards in the field of Low Temperature Plasma Physics. In 2017, he won Laboratory Astrophysics Prize of the American Astronomical Society for research in spectroscopy.
Longtime collaborator Blair Savage, UW–Madison professor emeritus of astronomy, says:
“Jim’s work in laboratory astrophysics provided extremely important atomic ultraviolet transition probabilities in support of the Hubble Space Telescope programs to determine elemental abundances of gaseous matter in the interstellar medium from three different ultraviolet spectrographs over the 32-year history of the space observatory. They included the Goddard High Resolution Spectrograph, the Space Telescope Imaging Spectrograph and the Cosmic Origins Spectrograph.”
And Wilmer Anderson, Lawler’s doctoral advisor, says:
“He was a very good graduate student, and he of course has turned out to be a really great scientist and colleague. His lifetime measurements on atomic physics played a key role in understanding the neutron star collisions. I’m sorry to see him retiring but I’m sure that he will leave a legacy behind that’s really fantastic. It’s going to be a big loss to the department not to have him around.”
Lawler has collaborated with his AMO colleagues over the years, but in more of an intellectual capacity than in research. As he notes, much of AMO is headed in the quantum information and quantum computing direction, with public and private funding helping to drive it. Still, he does not see AMO headed solely in the quantum direction.
“Decades from now the currently Hot areas of physics will be less glamorous, but those stars are still going to be light years away,” Lawler says. “I think the connection of astronomy and spectroscopy — the way we learn about the physics and chemistry of the remote universe — is strong enough that it will survive. And helping make spectroscopy in astronomy more quantitative is what we’ve done that will have some lasting significance.”
Ultraprecise atomic clock poised for new physics discoveries
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.
“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
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.
Shimon Kolkowitz earns NSF CAREER award
Shimon Kolkowitz has already developed one of the most precise atomic clocks ever. Now, the UW–Madison physics professor has been awarded a Faculty Early Career Development (CAREER) award from the National Science Foundation (NSF) to use his atomic clocks to potentially answer some big questions about the physics of our universe.
The five-year, $800,000 in total award will cover research expenses, graduate student support, and outreach projects based on the research.
“I am honored and proud to receive an NSF CAREER award, which will help my research group expand our experimental efforts and build upon our recent results,” Kolkowitz says. “This award will support research into new ways to harness the remarkable precision of optical atomic clocks for exciting physics applications such as searching for dark matter and detecting gravitational waves.”
Atomic clocks are so precise because they take advantage of the natural vibration frequencies of atoms, which are identical for all atoms of a particular element. Kolkowitz and his research group have developed atomic clocks that can detect the difference in these frequencies between two clocks that would only disagree with each other by one second after 300 billion years, the tiniest detectable frequency changes to date. These clocks, then, can measure effects that shifts their frequency by only 0.00000000000000001%, opening the possibility of using them in the search for new physics.
A significant advancement in Kolkowitz’s clocks is that they are multiplexed, with six or more separate clocks in one
vacuum chamber, effectively placing each clock in the same environment. Mutliplexing means that comparisons between the clocks, and not their individual accuracy, is what matters — and allows the group to use commercially available, robust and portable lasers in their measurements. Though the clocks are not yet ready to be used to detect gravitational waves, Kolkowitz says the current setup “looks a bit like how you would eventually do that,” and will allow him to test out and demonstrate the concept.
In the spirit of the Wisconsin Idea and the NSF’s “broader impacts” to benefit society beyond scientific merit, with this award, Kolkowitz will focus efforts on quantum science outreach with pre-college students.
“We’ll be developing new demos and hands-on activities designed to introduce K-12 students to modern physics concepts,” Kolkowitz says. “We’ll use these activities to engage students at live shows and interactive events as part of The Wonders of Physics outreach program, with an emphasis on reaching rural and Native American communities in Wisconsin.”
NSF established these awards to help scientists and engineers develop simultaneously their contributions to research and education early in their careers. CAREER funds are awarded by the federal agency to junior-level faculty at colleges and universities.
Deniz Yavuz announced as Vilas Associate
The Office of the Vice Chancellor for Research and Graduate Education has announced 23 faculty winners of the Vilas Associates Competition, including physics professor Deniz Yavuz. The Vilas Associates Competition recognizes new and ongoing research of the highest quality and significance.
The award is funded by the William F. Vilas Estate Trust.
Recipients are chosen competitively by the divisional research committees on the basis of a detailed proposal. Winners receive up to two-ninths of research salary support (including the associated fringe costs) for both summers 2021 and 2022, as well as a $12,500 flexible research fund in each of the two fiscal years. Faculty paid on an annual basis are not eligible for the summer salary support but are eligible for the flexible fund portion of this award.
Physics alum, professor emeritus Barney Webb remembered for his many contributions to the University and his field
University of Wisconsin–Madison Professor Emeritus Maurice Barnett “Barney” Webb passed away January 15, 2021 in Middleton, WI. He was 94.
Born and raised in Neenah, WI in 1926, Professor Webb earned his both his bachelor’s (’50) and doctoral (’56) degrees from the UW–Madison Physics Department. After graduating, he went to work at General Electric Research Laboratory as a staff scientist. In 1961, he returned to UW–Madison as a tenured Associate Professor of Physics.
Barney served as Department Chair from 1971-1973, taking the reins of a department that had been traumatized by the 1970 Sterling Hall bombing. In 1977, he was named chair of the University Committee, the Executive Committee of the faculty and the most important and visible manifestation of faculty governance at UW–Madison. From 1985-1990, he served as Chair of the UW–Madison Athletic Board. He was an Emeritus Professor with the department since his retirement in 2001.
Remarkably, Barney was as prominent in the scientific community as he was on campus. His research interests included surface physics, low-energy electron diffraction, and scanning tunneling microscopy. In 1987, he was awarded the Davisson-Germer Prize in Atomic or Surface Physics from the American Physical Society “For his contribution to the development of low-energy electron diffraction as a quantitative probe of the crystallography defect structure, and dynamics of surfaces.”
Several UW–Madison colleagues recently reflected on their time with Barney.
Of Barney’s competitive academic research program, Emeritus Professor Franz Himpsel says,
“It is particularly notable that during Barney’s career, the big industrial research labs (Bell Labs, IBM, Xerox) dominated at the cutting edge of research in condensed matter and surface physics — Barney’s specialties. Compared to a university professor, their research staff members had vast resources available — not only financially but also via interactions with expert in-house colleagues. Despite the odds, Barney kept up with them by devising clever experiments and building most of his equipment together with his students.”
Current materials science and engineering professor and former student of Barney’s, Max Lagally, recalls, “What always scared me is when Barney started saying ‘I don’t know anything about this, but…’ and then proceeded to demonstrate that he knew all about it.”
Emeritus Professor Louis Bruch noted that Barney’s competitive edge carried over to interests outside the lab. Bruch says, “He was a competitive gardener, for instance on the question of first ripe tomatoes and last ripe strawberries.” And Professor Pupa Gilbert recalls, “Barney had a terrific sense of humor, and was an intrepid cyclist for most of his life. As he aged, he said that uphill roads ‘got steeper and steeper,’ so he stopped biking on them.”
Professor Mark Eriksson says that Barney was a great mentor and role model, always understated about his own accomplishments, and always willing to offer advice when asked.
“This was certainly true throughout my time on the faculty since 1999, when Barney was supportive and encouraging from day one. But it was true for me far earlier than that. At 9am on February 28, 1987, I met with Professor Webb in his office. He had agreed to talk to my father and me about choosing an undergraduate college, since I was interested in physics. I was a 17-year-old high school junior from Madison LaFollette. Barney didn’t know either my father or me, and the 28th was a Saturday. None of that mattered, and he was happy to take the time to talk with us. When I joined the faculty years later, I of course remembered that conversation, and so did he.”
Professor Bob Joynt says, “I probably had lunch with Barney 4000 times over 30 years, the last time when he was 92 and still coming in pretty much every day. He was the same age as my father. However, he was not a mentor but a protector. He shielded me every day from everything that is boring in life – he was a person always interested in everything and approached it all with the most lively intellect. I never remember a moment in his company that was not absorbing and fun.”
Shimon Kolkowitz awarded two grants to push optical atomic clocks past the standard quantum limit
Optical atomic clocks are already the gold standard for precision timekeeping, keeping time so accurately that they would only lose one second every 14 billion years. Still, they could be made to be even more precise if they could be pushed past the current limits imposed on them by quantum mechanics.
With two new grants from the U.S. Army Research Office, an element of the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory, UW–Madison physics professor Shimon Kolkowitz proposes to introduce quantum entanglement — where atoms interact with each other even when physically distant — to optical atomic clocks. The improved clocks would allow researchers to ask questions about fundamental physics, and they have applications in improving quantum computing and GPS.
Atomic clocks are so precise because they take advantage of the natural vibration frequencies of atoms, which are identical for all atoms of a particular element. These clocks operate at or near the standard quantum limit, a fundamental limit on performance imposed on clocks where the atoms are all independent of each other. The only way to push the clocks past that limit is to achieve entangled states, strange quantum states where the atoms are no longer independent and they become intertwined.
“That turns out to be hard for a number of reasons. Entanglement requires these atoms to interact with each other, but a good clock requires them not to interact with each other or anything else,” Kolkowitz says. “So, you need to engineer a situation where you can make the atoms interact strongly, but you can also switch those interactions off. And those are some of the same requirements that are necessary for quantum computing.”
Kolkowitz is already building an optical atomic clock in his lab, albeit one that is not yet using entangled states. To make the clock, they first laser-cool strontium atoms to one millionth of one degree Celsius above absolute zero, then load the atoms into an optical lattice. In the lattice, the atoms are separated into what is effectively a tiny stack of pancakes — each atom can move around within their own flat disk, but they cannot jump into another pancake.
Though the atoms’ are stuck in their own pancake, they can interact with each other if their electrons are highly excited. This type of atom, known as Rydberg atoms, becomes close to one million times larger than an unexcited counterpart because the excited electron can be microns away from the nucleus.
“It’s kind of crazy that a single atom can be that big, and when you make them that much bigger, they interact much more strongly with each other than they do in their ground states,” Kolkowitz says. “Basically it means you can go from the atoms not interacting at all to interacting very strongly. That’s exactly what you want for quantum computing, and it’s what you want for this atomic clock.”
With the two ARO grants, Kolkowitz expects to generate Rydberg atoms in his lab’s atomic clock. One of the grants, a Defense University Research Instrumentation Program (DURIP), will fund the specialized UV laser that generates the high energy photons needed to excite the atoms into the highly excited Rydberg states. The second grant will fund personnel and other supplies. Kolkowitz will collaborate with UW–Madison physics professor Mark Saffman, who, along with physics professor Thad Walker, pioneered the use of Rydberg atoms for quantum computing.
In addition to being useful for developing new approaches to ask questions about fundamental physics in his research lab, these ultraprecise atomic clocks are of interest to the Department of Defense for atomic clock-based technologies such as GPS, and because they can be used to precisely map Earth’s gravity.