Research, teaching and outreach in Physics at UW–Madison
Physics projects funded in first round of UW’s Research Forward initiative
In its inaugural round of funding, the Office of the Vice Chancellor for Research and Graduate Education’s (OVCRGE) Research Forward initiative selected 11 projects, including two with physics department faculty involvement.
OVCRGE hosts Research Forward to stimulate and support highly innovative and groundbreaking research at the University of Wisconsin–Madison. The initiative is supported by the Wisconsin Alumni Research Foundation (WARF) and will provide funding for 1–2 years, depending on the needs and scope of the project.
Research Forward seeks to support collaborative, multidisciplinary, multi-investigator research projects that are high-risk, high-impact, and transformative. It seeks to fund research projects that have the potential to fundamentally transform a field of study as well as projects that require significant development prior to the submission of applications for external funding. Collaborative research proposals are welcome from within any of the four divisions (Arts & Humanities, Biological Sciences, Physical Sciences, Social Sciences), as are cross-divisional collaborations.
Correlated errors in quantum computers emphasize need for design changes
Quantum computers could outperform classical computers at many tasks, but only if the errors that are an inevitable part of computational tasks are isolated rather than widespread events.
Now, researchers at the University of Wisconsin–Madison have found evidence that errors are correlated across an entire superconducting quantum computing chip — highlighting a problem that must be acknowledged and addressed in the quest for fault-tolerant quantum computers.
The researchers report their findings in a study published June 16 in the journal Nature, Importantly, their work also points to mitigation strategies.
“I think people have been approaching the problem of error correction in an overly optimistic way, blindly making the assumption that errors are not correlated,” says UW–Madison physics Professor Robert McDermott, senior author of the study. “Our experiments show absolutely that errors are correlated, but as we identify problems and develop a deep physical understanding, we’re going to find ways to work around them.”
CHIME telescope detects more than 500 mysterious fast radio bursts in its first year of operation
This post has been modified from the original post, published by MIT News
To catch sight of a fast radio burst is to be extremely lucky in where and when you point your radio dish. Fast radio bursts, or FRBs, are oddly bright flashes of light, registering in the radio band of the electromagnetic spectrum, that blaze for a few milliseconds before vanishing without a trace.
These brief and mysterious beacons have been spotted in various and distant parts of the universe, as well as in our own galaxy. Their origins are unknown, and their appearance is unpredictable. Since the first was discovered in 2007, radio astronomers have only caught sight of around 140 bursts in their scopes.
Now, a large stationary radio telescope in British Columbia has nearly quadrupled the number of fast radio bursts discovered to date. The telescope, known as CHIME, for the Canadian Hydrogen Intensity Mapping Experiment, has detected 535 new fast radio bursts during its first year of operation, between 2018 and 2019.
Scientists with the CHIME Collaboration, including researchers at the University of Wisconsin–Madison, have assembled the new signals in the telescope’s first FRB catalog, which they will present this week at the American Astronomical Society Meeting.
UW–Madison physics professor Moritz Münchmeyer is a member of CHIME-FRB and contributed to the statistical analysis of the new FRB catalog. He joined UW–Madison this spring and a part of his new group is continuing this work, with the goal of using FRBs as a novel probe of the physics of the universe.
“This is only the beginning of FRB research. For the first time we now have enough FRBs to study their statistical distribution. It turns out that FRBs come from all over the universe, from relatively nearby to half way back to the Big Bang,” Münchmeyer says. “They are also quite frequent, about 800 per day if we were to see them all. They are extremely powerful light sources at cosmological distances and thus provide a new window into the physics of the universe.”
The Dark Energy Survey collaboration has created the largest ever maps of the distribution and shapes of galaxies, tracing both ordinary and dark matter in the universe out to a distance of more than 7 billion light years. The analysis, which includes the first three years of data from the survey, is consistent with predictions from the current best model of the universe, the standard cosmological model. Nevertheless, there remain hints from DES and other experiments that matter in the current universe is a few percent less clumpy than predicted.
New results from the Dark Energy Survey — a large international team that includes researchers from the University of Wisconsin–Madison — use the largest ever sample of galaxies over an enormous piece of the sky to produce the most precise measurements of the universe’s composition and growth to date. Scientists measured that the way matter is distributed throughout the universe is consistent with predictions in the standard cosmological model, the best current model of the universe.
Over the course of six years, DES surveyed 5,000 square degrees — almost one-eighth of the entire sky — in 758 nights of observation, cataloguing hundreds of millions of objects. The results, announced May 27, draw on data from the first three years — 226 million galaxies observed over 345 nights — to create the largest and most precise maps yet of the distribution of galaxies in the universe at relatively recent epochs.
Since DES studied nearby galaxies as well as those billions of light-years away, its maps provide both a snapshot of the current large-scale structure of the universe and a movie of how that structure has evolved over the course of the past 7 billion years.
“This a stringent test of the current standard cosmological paradigm, a model proposing that 95% of the universe is dark matter and dark energy that we do not yet understand,” explains UW–Madison physics professor Keith Bechtol. “By measuring the apparent positions and shapes of hundreds of millions of galaxies in our survey, we test whether the cosmic structures that have formed in the universe today match the predictions based on structures observed in the early universe.”
To test cosmologists’ current model of the universe, DES scientists compared their results with measurements from the European Space Agency’s orbiting Planck observatory. Planck used light signals known as the cosmic microwave background to peer back to the early universe, just 400,000 years after the Big Bang. The Planck data give a precise view of the universe 13 billion years ago, and the standard cosmological model predicts how the dark matter should evolve to the present. If DES’s observations don’t match this prediction, there is possibly an undiscovered aspect to the universe. While there have been persistent hints from DES and several previous galaxy surveys that the current universe is a few percent less clumpy than predicted—an intriguing find worthy of further investigation—the recently released results are consistent with the prediction.
“In the area of constraining what we know about the distribution and structure of matter on large scales as driven by dark matter and dark energy, DES has obtained limits that rival and complement those from the cosmic microwave background,” said Brian Yanny, a Fermilab scientist who coordinated DES data processing and management. “It’s exciting to have precise measurements of what’s out there and a better understanding of how the universe has changed from its infancy through to today.”
Ordinary matter makes up only about 5% of the universe. Dark energy, which cosmologists hypothesize drives the accelerating expansion of the universe by counteracting the force of gravity, accounts for about 70%. The last 25% is dark matter, whose gravitational influence binds galaxies together. Both dark matter and dark energy remain invisible and mysterious, but DES seeks to illuminate their natures by studying how the competition between them shapes the large-scale structure of the universe over cosmic time.
DES photographed the night sky using the 570-megapixel Dark Energy Camera on the Victor M. Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory in Chile, a Program of the National Science Foundation’s NOIRLab. One of the most powerful digital cameras in the world, the Dark Energy Camera was designed specifically for DES and built and tested at Fermilab. The DES data were processed at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign.
“These analyses are truly state-of-the-art, requiring artificial intelligence and high-performance computing super-charged by the smartest young scientists around,” said Scott Dodelson, a physicist at Carnegie Mellon University who co-leads the DES Science Committee with Elisabeth Krause of the University of Arizona. “What an honor to be part of this team.”
To quantify the distribution of dark matter and the effect of dark energy, DES relied on two main phenomena. First, on large scales, galaxies are not distributed randomly throughout space but rather form a weblike structure due to the gravity of dark matter. DES measured how this cosmic web has evolved over the history of the universe. The galaxy clustering that forms the cosmic web, in turn, revealed regions with a higher density of dark matter.
Second, DES detected the signature of dark matter through weak gravitational lensing. As light from a distant galaxy travels through space, the gravity of both ordinary and dark matter can bend it, resulting in a distorted image of the galaxy as seen from Earth. By studying how the apparent shapes of distant galaxies are aligned with each other and with the positions of nearby galaxies along the line of sight, DES scientists inferred the spatial distribution (or clumpiness) of the dark matter in the universe.
Analyzing the massive amounts of data collected by DES was a formidable undertaking. The team began by analyzing just the first year of data, which was released in 2017. That process prepared the researchers to use more sophisticated techniques for analyzing the larger data set, which includes the largest sample of galaxies ever used to study weak gravitational lensing.
For example, calculating the redshift of a galaxy — the change in light’s wavelength due to the expansion of the universe — is a key step toward measuring how both galaxy clustering and weak gravitational lensing change over cosmic history. The redshift of a galaxy is related to its distance, which allows the clustering to be characterized in both space and time.
“Redshift calibration is one topic where we significantly improved upon our year-1 data analysis,” said Ross Cawthon, a UW-Madison physics postdoc who led the redshift calibration efforts for two of the main galaxy samples. “We developed new methods and refined old ones. It has been a huge effort by DES members from all over the world.”
Ten regions of the sky were chosen as “deep fields” that the Dark Energy Camera imaged repeatedly throughout the survey. Stacking those images together allowed the scientists to glimpse more distant galaxies. The team then used the redshift information from the deep fields to calibrate measurements of redshift in the rest of the survey region. This and other advancements in measurements and modeling, coupled with a threefold increase in data compared to the first year, enabled the team to pin down the density and clumpiness of the universe with unprecedented precision.
Along with the analysis of the weak-lensing signals, DES also precisely measures other probes that constrain the cosmological model in independent ways: galaxy clustering on larger scales (baryon acoustic oscillations), the frequency of massive clusters of galaxies, and high-precision measurements of the brightnesses and redshifts of Type Ia supernovae. These additional measurements will be combined with the current weak-lensing analysis to yield even more stringent constraints on the standard model.
“DES has delivered cost-effective, leading-edge science results directly related to Fermilab’s mission of pursuing the fundamental nature of matter, energy, space and time,” said Fermilab Director Nigel Lockyer. “A dedicated team of scientists, engineers and technicians from institutions around the world brought DES to fruition.”
The DES collaboration consists of over 400 scientists from 25 institutions in seven countries.
“The collaboration is remarkably young. It’s tilted strongly in the direction of postdocs and graduate students who are doing a huge amount of this work,” said DES Director and spokesperson Rich Kron, who is a Fermilab and University of Chicago scientist. “That’s really gratifying. A new generation of cosmologists are being trained using the Dark Energy Survey.”
UW–Madison physics graduate student Megan Tabbutt was one of the many significant contributors to this work, developing new methods that contributed to an independent validation of the galaxy clustering analysis.
DES concluded observations of the night sky in 2019. With the experience of analyzing the first half of the data, the team is now prepared to handle the complete data set. The final DES analysis is expected to paint an even more precise picture of the dark matter and dark energy in the universe. And the methods developed by the team have paved the way for future sky surveys to probe the mysteries of the cosmos.
“This work represents a ‘big statement’ from the Dark Energy Survey. DES data combined with other observations provide world-leading constraints on the nature of dark energy,” Bechtol says. “At the same time, we are training a new generation of cosmologists, and pioneering advanced methodologies that will be essential to realize the full potential of upcoming galaxy surveys, including the Vera C. Rubin Observatory Legacy Survey of Space and Time.”
The recent DES results were presented in a scientific seminar on May 27. Twenty-nine papers are available on the arXiv online repository.
The Dark Energy Survey is a collaboration of more than 400 scientists from 25 institutions in seven countries. For more information about the survey, please visit the experiment’s website.
Flexible, easy-to-scale nanoribbons move graphene toward use in tech applications
From radio to television to the internet, telecommunications transmissions are simply information carried on light waves and converted to electrical signals.
Silicon-based fiber optics are currently the best structures for high-speed, long distance transmissions, but graphene — an all-carbon, ultra-thin and adaptable material — could improve performance even more.
In a study published April 16 in ACS Photonics, University of Wisconsin–Madison researchers fabricated graphene into the smallest ribbon structures to date using a method that makes scaling-up simple. In tests with these tiny ribbons, the scientists discovered they were closing in on the properties they needed to move graphene toward usefulness in telecommunications equipment.
“Previous research suggested that to be viable for telecommunication technologies, graphene would need to be structured prohibitively small over large areas, (which is) a fabrication nightmare,” says Joel Siegel, a UW–Madison graduate student in physics professor Victor Brar’s group and co-lead author of the study. “In our study, we created a scalable fabrication technique to make the smallest graphene ribbon structures yet and found that with modest further reductions in ribbon width, we can start getting to telecommunications range.”
New nondestructive optical technique reveals the structure of mother-of-pearl
Most people know mother-of-pearl, an iridescent biomineral also called nacre, from buttons, jewelry, instrument inlays and other decorative flourishes. Scientists, too, have admired and marveled at nacre for decades, not only for its beauty and optical properties but because of its exceptional toughness.
“It’s one of the most-studied natural biominerals,” says Pupa Gilbert, a University of Wisconsin–Madison physics professor who has studied nacre for more than a decade. “It may not look like much — just a shiny, decorative material. But it can be 3,000 times more resistant to fracture than aragonite, the mineral from which it’s made. It has piqued the interest of materials scientists because making materials better than the sum of their parts is extremely attractive.”
Now, a new, nondestructive optical technique will unlock even more knowledge about nacre, and in the process could lead to a new understanding of climate history. Gilbert, UW–Madison electrical engineering professor Mikhail Kats — who is also an affiliate professor of physics — their students, and collaborators described the technique, called hyperspectral interference tomography, today in the journal Proceedings of the National Academy of Sciences.
Highest-energy Cosmic Rays Detected in Star Clusters
For decades, researchers assumed the cosmic rays that regularly bombard Earth from the far reaches of the galaxy are born when stars go supernova — when they grow too massive to support the fusion occurring at their cores and explode.
Those gigantic explosions do indeed propel atomic particles at the speed of light great distances. However, new research suggests even supernovae — capable of devouring entire solar systems — are not strong enough to imbue particles with the sustained energies needed to reach petaelectronvolts (PeVs), the amount of kinetic energy attained by very high-energy cosmic rays.
And yet cosmic rays have been observed striking Earth’s atmosphere at exactly those velocities, their passage marked, for example, by the detection tanks at the High-Altitude Water Cherenkov (HAWC) observatory near Puebla, Mexico. Instead of supernovae, the researchers — including UW–Madison’s Ke Fang — posit that star clusters like the Cygnus Cocoon serve as PeVatrons — PeV accelerators — capable of moving particles across the galaxy at such high energy rates.
IceCube detection of a high-energy particle proves 60-year-old theory
On Dec. 8, 2016, a high-energy particle hurtled to Earth from outer space at close to the speed of light. The particle, an electron antineutrino, smashed into an electron deep inside the ice sheet at the South Pole. This collision produced a particle that quickly decayed into a shower of secondary particles, triggering the sensors of the IceCube Neutrino Observatory, a massive telescope buried in the Antarctic glacier.
IceCube had seen a Glashow resonance event, a phenomenon predicted by Nobel laureate physicist Sheldon Glashow in 1960. With this detection, scientists provided another confirmation of the Standard Model of particle physics. It also further demonstrated the ability of IceCube, which detects nearly massless particles called neutrinos using thousands of sensors embedded in the Antarctic ice, to do fundamental physics. The result was published March 10 in Nature.
Congratulations to Professor Sue Coppersmith on her retirement!
With the best of wishes — and some sadness — the Department of Physics says “Happy Retirement” to Professor Sue Coppersmith. Her last day at UW–Madison was February 14.
Coppersmith, the Robert E. Fassnacht Professor of Physics, joined the department in 2001. Prior to coming to UW–Madison, she earned her Ph.D. from Cornell University, conducting her thesis work at Bell Labs. She completed a postdoc at Brookhaven National Lab, then worked at Bell Labs for eight years before joining the faculty at the University of Chicago.
During her tenure here, she served as Department Chair for one three-year term, and earned recognition as a Fellow of the National Academy of Sciences, the American Academy of Arts and Sciences, the American Association for the Advancement of Science, and the American Physical Society.
At UChicago, Coppersmith’s research focused on soft matter physics and non-linear dynamics, work that she continued at UW–Madison, primarily with Prof. Pupa Gilbert. But her research program largely shifted over the years into quantum computing, an area that was just getting started when she started in Madison..
“At the time, I would tell people what we were doing, and of course nothing was working yet, and people would say, ‘Well, that’s all crap, isn’t it?’” Coppersmith recalls. “So, it was really fun to go from a time where there was nothing working, to now we have qubits, and being a part of the effort and feeling like I was helping.”
Coppersmith describes herself as a theorist who went into the lab every day to better understand the experimental side of quantum computing, And, she says, UW–Madison stands out as one of the universities where theory and experiment are so closely tied together. Here, she frequently collaborated with Prof. Mark Eriksson and Distinguished Scientist Mark Friesen.
“She just comes up with a lot of ideas, and what matters most is how many of them are home runs. She had an unusually large number,” Eriksson says. “She came up with the idea for a brand new qubit, the quantum dot hybrid qubit, and we’re still working on it to this day in my lab. And other people around the world have picked it up.”
“As a researcher, Sue is highly intuitive and focused more on the high-level physical picture rather than specific technical details. She typically breaks a problem down to a ‘minimal model’ that captures its basic physics. She has studied a wide variety of problems in her career, for which she is highly respected in many different communities, and she is able to apply lessons learned from one area to another. Her memory is legendary! She is also known for her quickness, both in being able to understand a problem (and how it fits into the big picture) and being able to immediately respond to it. I also say this in a good way: she is not shy about expressing her opinions.”
Legacy as Department Chair
Perhaps equal to her scientific achievements is the mark Coppersmith made on the department during her time as Chair, from 2005-08. The Department was hiring three faculty positions, and she reasoned that if eight offers were made, at worst four people would accept.
“But eight people came! And I was famous for it because I ruined the College’s budget,” Coppersmith says. “I think this is the highlight of my Chair career. I loved recruiting people.”
There are a number of factors that go into faculty candidates accepting or not accepting offers, but Eriksson is certain that Coppersmith‘s ability to recruit was a significant one.
“They came in large part because Sue understood and was able to get them to explain and she was able to hear what they really needed, and then go deliver on it,” Eriksson says. “It’s one thing to have any subset of those skills, but she has the whole package.”
Current Department Chair Sridhara Dasu credits Coppersmith with shaping the direction of the department in all areas of physics, adding, “Her tenure continues to be an inspiration for all chairs of the department who followed her.”
Mentorship of students and colleagues
Coppersmith’s mentorship of junior colleagues and students will also be missed. Both Friesen and Susan Nossal, senior scientist and director of the Physics Learning Center, noted that Coppersmith’s support has been crucial to their success as researchers in the department. They both applauded her as a champion of women and girls in science, citing her participation – with Nossal, Gilbert and several graduate students – in the annual Expanding Your Horizons event at which middle school girls participate in fun, hands-on science activities.
“As a mentor, she is highly dedicated to her students and colleagues,” says Friesen, who co-advised several students with Coppersmith. “For me personally, she has been very supportive of my career path, helping me to obtain promotions and advancements, and providing on-point advice.”
Adds Nossal: “As a scientist, you have your ups and downs, and she helped me through some of the downs. It’s always helpful to have people who believe in you, and she helped me in persisting as a scientist.”
Between Coppersmith and everyone else mentioned in this piece, there were certainly plenty of stories that could be shared. But for now, we’ll let emeritus professor Lou Bruch sum up Coppersmith’s tenacity and well-placed ambition with this anecdote:
“Sue touted the usefulness of the Mathematica package and would at times get into competition on speed of getting to the answer — her using the package and me using ad hoc analyses. I recall only one instance where I won.”
Coppersmith may be retired from UW–Madison, but she is not retiring from science. She is currently Professor and Head of the School of Physics at the University of New South Wales in Australia, where she will continue her research and collaborations with colleagues here and around the world.
“Wisconsin was so good to me. The people are so nice, and we did good work,” Coppersmith says. “I like to feel that I contributed in a positive way. I’ll always be grateful.”
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.