Welcome, Professor Uwe Bergmann!

profile photo of Uwe Bergmann
Uwe Bergmann

From bird feathers that allow for perfectly efficient flight to the bacterial enzyme that fixes nitrogen to help plants grow, nature has had a lot of time to figure things out. “There are so many things we need to be learning how to do from nature, because our methods are still much inferior to those!” says UW–Madison’s newest physics professor, Uwe Bergmann, the Martin L. Perl Professor in Ultrafast X-ray Science. “I think we are going in this direction of learning more and more from nature and using this knowledge to run our world sustainably, but still in a modern way. And that theme brings physicists and many other domains together.”

Bergmann is a physicist who develops and applies x-ray techniques to chemical, biological, engineering, and even archaeological research questions, trying to understand at the atomic level what nature has perfected over a few billion years. Prior to joining the Department on December 1, Bergmann was a Scientist at SLAC. Here, he will focus his research program on continuing to develop and apply novel x-ray techniques. To welcome Bergmann, we sat down for a (virtual) interview.

What is an overview of your research?

My research is developing and applying x-ray methods to solve problems. And these problems can be uncovering hidden writings in ancient books or the chemical elements buried in fossils to reveal the color in the original animal; studying photosynthetic water splitting to understanding the structure of liquid water; and making movies of a molecule carrying out specific work.

What techniques do you use in your research?

I use mainly x-ray techniques, and we do x-ray spectroscopy and sometimes also x-ray scattering and diffraction. The basic difference is that diffraction and scattering looks at the geometric structure — where are the atoms? — and spectroscopy looks at the chemical structure — where are the electrons? Recently we have been using powerful new x-ray lasers, where you can make ultrafast movies showing how chemical bonds are changing in real time. I also use x-ray fluorescence, which is a very powerful imaging technique for creating elemental maps showing the chemical composition of fossils for example.

Once your lab is up and running in Madison, what big projects will you focus on first?

I want to set up a new ultrafast x-UV laser system, able to making these molecular movies with femtosecond resolution. We want to make movies of fast chemical reactions and structural changes; when you expose a material to a light pulse and then watch how the atoms and electrons rearrange after the pulse. This is important for the next generation of advanced materials and a famous example is the water splitting reaction in plants to make O2. We still do not exactly know the mechanism of how these two water molecules are brought in, split up, and forced to make the bond to form O2.

In our latest project with x-ray fluorescence imaging we have scanned more than 50 pages of an ancient parchment book containing the work of the famous Greek physician, Galen of Pergamon. This so-called palimpsest contains a Syriac translation with his work including ‘On Simple Drugs’, which had been erased and overwritten with hymns in the Middle Ages, and catalogued as a new find at Saint Catherine’s Monastery in 1975. Scholars are interested in this translation as it gives information of how Galen’s work originally written in Greek spread east, were it became very popular in the Arab world. Using powerful synchrotron x-rays, we found that you can actually bring out this erased and overwritten text. And scholars can now read it! Key to this success was our new scanning system that records the whole x-ray fluorescence spectrum at each pixel of the image, and our collaborators’ ability to apply advanced machine learning algorithms to enhance the faint traces of overwritten text.

Another exciting project we are working on is an x-ray laser oscillator. There are currently five very big hard x-ray free electron lasers around the world, but they operate in a single pass, which means they are not very stable. Our idea is to use a train of pulses from one of these big x-ray lasers — those are the not-so-clean pulses — to pump our gain medium. After the first pulse creates amplified spontaneous emission, we guide the emitted beam through a cavity made of four mirrors back to the same gain medium to meet up with the next pump pulse from the train. Doing this again and again and again, lets us crank up the beam until we have a perfect, clean and stable x-ray laser pulse, and at the point we will send it out of the cavity. This is similar to how most optical lasers work. We described the idea in PNAS earlier this year, and now we have a lot of work ahead to turn it into reality.

What attracted you to UW–Madison?

For some time, I have been thinking whether it would be possible one day to combine my research activities with teaching at a university. The ultrafast x-ray science chair in the Physics Department was a perfect opportunity and an excellent fit to the research I have been pursuing my entire career. Still, it wasn’t until my visit to Madison, experiencing the wonderful interaction with the students, faculty and staff, and feeling the energy on this beautiful campus, that I fell in love with the idea of joining UW–Madison.

What is your favorite element and/or elementary particle?

Manganese is my favorite element, just because I have been spending so many years studying it and it has so many amazing properties. It’s chemically very important as it has all these different oxidation states, ranging from +2 to +7. And it’s at the heart of the tiny little machine driven by sun light that nature uses to split water into oxygen, which I think is the most important reaction on the planet. Without that reaction there would only be primitive bacterial life on earth. For the elementary particle, I feel almost ashamed but of course it has to be the electron, because it does all the work. Nuclei hardly notice any chemical change, but electrons do all the bonding, all the rearrangements that make the world run; they are the worker bees of nature.

What hobbies/other interests do you have?

I love nature, animals, music, and outdoor activities, especially in and around water.


High Energy Physics group awarded three grants totaling over $14 million

a woman in a helmet wearing a disposable facemask stands in front of lots of metal hardware and wires
HEP post-doc Dr. Camilla Galloni next to the CMS end cap supporting the GEM detectors that were installed this fall. The primary structure in this photo was engineered at the UW–Madison Physical Sciences Lab. The big CSC chambers were installed, upgraded and reinstalled and operated by UW physicists. The smaller GEM chambers, which are barely visible in the interstices, are being commissioned by UW–Madison physicists through the second grant mentioned in this post.

The High Energy Physics (HEP) group at UW–Madison, which broadly focuses on identifying and understanding the fundamental aspects of particles and forces in Nature, has been awarded three significant grants in 2020. The grants — two from the Department of Energy (DOE) and one from the National Science Foundation (NSF) — are awarded either directly to UW–Madison or indirectly through multi-institution international collaborations, bringing over $14 million to the department.

The first grant, $7.37 million from DOE, funds research that is expected to help physicists understand how our Universe works at its most fundamental level. At UW­–Madison, this research includes experimental and theoretical studies into topics such as using the Higgs boson as a tool for new discoveries and identifying principles of dark matter.

The grant will fund five areas of research: 1) studies of high energy proton-proton collisions; 2) studies of neutrino interactions; 3) studies of super-weak signals from galactic dark matter particles; 4) wide-area imaging surveys using powerful new telescopes; and 5) computational and mathematical methods of quantum field theory and string theory.

Sridhara Dasu is principal investigator on this DOE grant. Co-investigators include Yang Bai, Vernon Barger, Keith Bechtol, Kevin Black, Tulika Bose, Lisa Everett, Matthew Herndon, Kimberly Palladino, Brian Rebel, Gary Shiu, Jennifer Thomas (WIPAC), and Sau Lan Wu. The grant was awarded in June 2020 and provides funding through March 2023.

The other two grants awarded will provide funding for upgrades to the Compact Muon Solenoid (CMS) project at the Large Hadron Collider (LHC) at CERN. The first is an NSF-funded grant for which Kevin Black is leading the UW–Madison effort to upgrade the CMS End Cap muon system upgrade. The $900,000 to the department is part of a larger multi-institutional grant through Cornell University and runs through 2025.

“The GEM detectors are novel micropattern gas detectors which can handle the high background rates expected in the end-cap muon detectors. They will enhance the triggering and reconstruction of forward muons which are expected to make significant improvements and increased acceptance to search for new particles and make precision measurements of known particles and interactions,” Black explains. “UW has a long history with CMS muon system with Prof Matt Herndon, Senior Emeritus Scientist Dick Loveless, and Senior Scientist Armando Lanaro leading to the design, construction, operation, and upgrade of the other end-cap subdetector system instrumented with Cathode Strip Chambers.”

The other CMS-specific grant is a four-year, $5.3 million DOE grant through Fermilab that will fund the CMS trigger upgrade. This funding will allow the UW–Madison CMS group to perform all aspects of the work involved in design, prototyping, qualification, production and validation of the calorimeter trigger system for the upgrade. When completed, the project is expected to result in the collection of 25 times more data than is currently possible. Sridhara Dasu is the principal investigator of this grant.

Ellen Zweibel elected AAAS Fellow

Congrats to Astronomy and Physics professor Ellen Zweibel on her election as a Fellow of the American Association for the Advancement of Science. She was elected “for distinguished contributions to quantify the role of magnetic fields in shaping the cosmos on all scales.” Read the full story about all six UW–Madison faculty who earned this honor.

Cary Forest, Jay Anderson, and John Wallace part of WARF Innovation Awards finalist team

profile photo of Cary Forest

Each fall the WARF Innovation Awards recognize some of the best of inventions at UW-Madison.

WARF receives hundreds of new invention disclosures each year. Of these disclosures, the WARF Innovation Award finalists are considered exceptional in the following criteria:


  • Has potential for high long-term impact
  • Presents an exciting solution to a known important problem
  • Could produce broad benefits for humankind

Cary Forest, Jay Anderson, and John Wallace are part of one of six finalists teams selected by WARF for their disclosure, “High-Energy Plasma Generator for Medical Isotope Production, Nuclear Waste Disposal & Power Generation.” Watch Video

Two Innovation Award winners will receive $10,000, split among UW inventors, and will be named at a virtual ceremony December 8. Learn more and register for the event.

See all six finalists and watch their videos at WARF’s Innovation Awards website.

Jimena González named Three Minute Thesis® finalist

Congrats to Jimena González, a physics graduate student in Keith Bechtol’s group, who is one of nine finalists for UW–Madison’s Three Minute Thesis® competition! Watch Jimena’s video on YouTube, and check out all nine finalists’ videos at the UW–Madison 3MT® website. The videos are only available through November 29. The finals will be held on February 3, 2021.

a still from a YouTube video of Jimena giving a presentation
Jimena González presents a virtual 3MT

A better understanding of coral skeleton growth suggests ways to restore reefs

Coral reefs are vibrant communities that host a quarter of all species in the ocean and are indirectly crucial to the survival of the rest. But they are slowly dying — some estimates say 30 to 50 percent of reefs have been lost — due to climate change.

In a new study, University of Wisconsin–Madison physicists observed reef-forming corals at the nanoscale and identified how they create their skeletons. The results provide an explanation for how corals are resistant to acidifying oceans caused by rising carbon dioxide levels and suggest that controlling water temperature, not acidity, is crucial to mitigating loss and restoring reefs.

“Coral reefs are currently threatened by climate change. It’s not in the future, it’s in the present,” says Pupa Gilbert, a physics professor at UW–Madison and senior author of the study. “How corals deposit their skeletons is fundamentally important to assess and help their survival.”

Read the Full Story | Link to the PNAS study

Surprising communication between atoms could improve quantum computing

A dark room with pink-hued lasers reflecting off of mirrors
In their experiments, UW–Madison physicists led by Deniz Yavuz immobilized a group of rubidium atoms by laser-cooling them to just slightly above absolute zero. Then, they shined a laser at rubidium’s excitation wavelength to energize electrons. PHOTO COURTESY OF YAVUZ LAB

A group of University of Wisconsin­–Madison physicists has identified conditions under which relatively distant atoms communicate with each other in ways that had previously only been seen in atoms closer together — a development that could have applications to quantum computing.

The physicists’ findings, published Oct. 14 in the journal Physical Review A, open up new prospects for generating entangled atoms, the term given to atoms that share information at large distances, which are important for quantum communications and the development of quantum computers.

“Building a quantum computer is very tough, so one approach is that you build smaller modules that can talk to each other,” says Deniz Yavuz, a UW–Madison physics professor and senior author of the study. “This effect we’re seeing could be used to increase the communication between these modules.”

profile photo of Deniz Yavuz
Deniz Yavuz

The scenario at hand depends on the interplay between light and the electrons that orbit atoms. An electron that has been hit with a photon of light can be excited to a higher energy state. But electrons loathe excess energy, so they quickly shed it by emitting a photon in a process known as decay. The photons atoms release have less energy than the ones that boosted the electron up — the same phenomenon that causes some chemicals to fluoresce, or some jellyfish to have a green-glowing ring.

“Now, the problem gets very interesting if you have more than one atom,” says Yavuz. “The presence of other atoms modifies the decay of each atom; they talk to each other.”

Read the full  UW–Madison news story

Chuanhong (Vincent) Liu named to Fall 2020 cohort of the Quantum Information Science and Engineering Network (QISE-NET)

Graduate student Chuanhong (Vincent) Liu (McDermott Group) has had his project awarded funding through QISE-NET, the Quantum Information Science and Engineering Network. Run through the University of Chicago, QISE-NET is open to any student pursuing an advanced degree in any field of quantum science. Liu and other students in his cohort earn up to three years of support, including funding, mentoring and training at annual workshops. All awardees are paired with a mentoring QISE company or national lab, at which they will complete part of their projects. Liu describes his project, below. Cecilia Vollbrecht, a grad student in Chemistry, also earned this honor. Both Liu and Volbrecht are students in the Wisconsin Quantum Institute.

The Single Flux Quantum (SFQ) digital logic family has been proposed as a scalable approach for the control of next-generation multiqubit arrays. With NIST’s strong track record in the field of SFQ digital logic and the expertise of McDermott’s lab in the superconducting qubit area, we expect to achieve high fidelity SFQ-based qubit control. The successful completion of this research program will represent a major step forward in the development of a scalable quantum-classical interface, a critical component of a fully error-corrected fault-tolerant quantum computer.

New study provides understanding of astrophysical plasma dynamics

Stars, solar systems, and even entire galaxies form when astrophysical plasma — the flowing, molten mix of ions and electrons that makes up 99% of the universe — orbits around a dense object and attaches, or accretes, on to it. Physicists have developed models to explain the dynamics of this process, but in the absence of sending probes to developing stars, the experimental confirmation has been hard to come by.

In a study published in Physical Review Letters September 25, University of Wisconsin–Madison physicists recreated an astrophysical plasma in the lab, allowing them to investigate the plasma dynamics that explain the accretion disk formation. They found that electrons, not the momentum-carrying ions, dominate the magnetic field dynamics in less dense plasmas, a broad category that includes nearly all laboratory astrophysical plasma experiments.

plasma from a sun-like star in the upper left corner is coming out like a string that swirls like a whirlpool around a dot in the center of the image
An artist’s conception of the accretion disk | Credit: P. Marenfeld/NOAO/AURA/NSF

Like water swirling around and down an open drain, plasma in an accretion disk spins faster nearer the heavy object in the center than further away. As the plasma falls inward, it loses angular momentum. A basic physics principle says that angular momentum needs to be conserved, so the faster rotating plasma must be transferring its momentum away from the center.

“This is an outstanding problem in astrophysics — how does that angular momentum get transported in an accretion disk?” says Ken Flanagan, a postdoctoral researcher with the department of physics at UW–Madison and lead author of the study.

The simplest explanation is friction, but it was ruled out when the corresponding accretion times, in some cases, would be longer than the age of the universe. A model developed by theoretical physicists posits that turbulence, or the chaotic changes in plasma flow speeds, can explain the phenomenon on a more realistic time scale.

“So ad hoc, astrophysicists say, ‘Okay, there’s this much turbulence and that explains it,’” Flanagan says. “Which is good, but you need to call in the plasma physicists to piece together where that turbulence comes from.”

Flanagan and colleagues, including UW­–Madison physics professor Cary Forest, wanted to build off an idea that the turbulence was coming from an intrinsic property of some plasmas known as magnetorotational instability. This instability is seen in plasmas that are flowing fastest near the center and are in the presence of a weak magnetic field.

“And it’s lucky because there are weak magnetic fields all around the universe, and the flow profile in the accretion disks is set by the gravitational force,” Flanagan says. “So, we thought this plasma instability could be responsible for turbulence, and it explains how accretion disks work.”

To investigate if this intrinsic plasma instability explained the observation, the researchers turned to the Big Red Ball (BRB), a three-meter-wide hollow sphere with a 3000 magnets at its inner surface and various probes inside. They activate a plasma by ionizing gas inside the BRB, then applying a current to drive its movement.

a 3-meter-diameter sphere, painted red and with tons of probes all around it
The Big Red Ball is one of several pieces of scientific equipment being used to study the fundamental properties of plasma in order to better understand the universe, where the hot, ionized gas is abundant. | Photo by Jeff Miller / UW–Madison)

Because they had previously been encountering problems in driving very fast flows, they tried a new technique to drive the flow across the entire volume of plasma, as opposed to just the edges. Fortuitously, the BRB had magnetic field probes from a previous experiment still attached, and when they activated the plasma under these conditions, they found that this new flow setup amplified the magnetic field strength with a peak at the center nearly twenty times the baseline strength.

“We didn’t expect to see that at all, because usually in plasma physics the simplest model is to think of plasmas as one fluid with the heavier ions dominating momentum,” Flanagan says. “The results suggested that the plasma is in the Hall regime, which means the electrons and their motion are entirely responsible for the plasma moving around magnetic fields.”

If they were correct in assuming it was the Hall effect that was driving magnetic field amplification, the equations governing magnetic fields and electric currents say that if you drive the current in the opposite direction, the strength of the magnetic field would be canceled out. So, they switched the current and measured the magnetic field strength: it was zero, supporting the Hall regime explanation.

While the results are not directly applicable to the plasma accretion disks around, say, a very dense black hole, they do directly impact the earth-bound experiments that attempt to recreate and study them.

“Nearly all plasma astrophysical experiments operate in the Hall regime, and so this sort of large qualitative effect is something you’re going to have to pay attention to when you make these sorts of flows in laboratory astrophysical plasmas,” Flanagan says. “In that sense, this work has a pretty broad impact for lots of different research areas.”

This research was supported in part by the National Science Foundation (#1518115) and by the U.S. Department of Energy (#DE-SC0018266).