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.
Shimon Kolkowitz earns NSF CAREER award
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Shimon Kolkowitz
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.”
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.
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
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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
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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.
A 1996 celebration of Barney Webb (front row, center) and his career was attended by many students and colleagues. From left to right: Jim Schilling, Ray Phaneuf, Art Kotz, Bill Weber, Bill Packard, Barney, Ed Conrad, Bill Unertl, John Unguris, Brian Swartzentruber, Liz Moog, Max Lagally | Photo provided by Jim Schilling
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.”
Barney Webb (left) and his former student Ray Phaneuf (Ph.D. ’85) in February 2020.
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
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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.
WQI team named winners in international quantum research competition
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A WQI faculty team was one of 18 winners in the Innovare Advancement Center’s “Million Dollar International Quantum U Tech Accelerator” competition, which awarded a total of $1.35 million last week. The winning teams, including UW–Madison physics professors Shimon Kolkowitz and Mark Saffman, each earned $75,000 toward their proposed research.
The competition attracted nearly 250 proposals from teams across the world in the areas of quantum timing, sensing, computing and communications, and 36 teams were invited to present at the live virtual event.
