Research, teaching and outreach in Physics at UW–Madison
News Archives
Help IceCube decode signals from outer space in new Citizen Science project
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Every second, about 100 trillion neutrinos pass through your body unnoticed. At the South Pole, the IceCube Neutrino Observatory detects these elusive particles and works to identify their astronomical origins to help unlock mysteries of the universe. Such an undertaking requires a massive amount of data, with one terabyte of data recorded daily by IceCube. But organizing the data can be labor intensive. This is where the public can help.
Starting today, volunteers from anywhere can participate in the Name that Neutrino project led by IceCube researchers at Drexel University, which asks users to categorize IceCube data. Through the Zooniverse platform, volunteers can join in from the convenience of their own computer or phone. Name that Neutrino is open to everyone and will run for about 10 weeks.
Click “Tutorial” to learn about how to classify signals.
Watch the brief video and pick one of the five categories for signals.
Check out the “Field Guide” for more examples and information.
Royal visit strengthens WIPAC and IceCube’s partnership with Thailand
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A budding collaboration between the Wisconsin IceCube Particle Astrophysics Center and Chiang Mai University in Thailand took a grand turn with a visit to the Royal Palace in Bangkok. There, discussions between scientists from WIPAC, a University of Wisconsin–Madison research center, and Her Royal Highness Princess Maha Chakri Sirindhorn explored how to increase research opportunities for Thai researchers and technical staff at the IceCube Neutrino Observatory.
IceCube, a unique telescope that has instrumented a billion tons of South Pole ice, searches for tiny, ghostlike particles called neutrinos to study the most powerful cosmic engines in the universe. HRH Sirindhorn’s fascination with physics, astronomy and Antarctic research has become evident in her strong advocacy for this work in general and IceCube science in particular.
The Wonders of Physics shows in Chamberlin Hall, Feb 11-12 and Feb 18-19, kept the audience riveted with scientific experiments that demonstrated physics principles with panache. It also was a landmark show of sorts, as Professor Clint Sprott handed over control to Haddie McLean in the show’s 40th year. The show aims to to generate interest in physics among people of all ages and backgrounds.
New quantum sensing technique reveals magnetic connections
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By Leah Hesla, Q-NEXT
A research team supported by the Q-NEXT quantum research center demonstrates a new way to use quantum sensors to tease out relationships between microscopic magnetic fields.
Say you notice a sudden drop in temperature on both your patio and kitchen thermometers. At first, you think it’s because of a cold snap, so you crank up the heat in your home. Then you realize that while the outside has indeed become colder, inside, someone left the refrigerator door open.
Initially, you thought the temperature drops were correlated. Later, you saw that they weren’t.
Recognizing when readings are correlated is important not only for your home heating bill but for all of science. It’s especially challenging when measuring properties of atoms.
Now scientists — including those from UW–Madison physics professor Shimon Kolkowitz‘s group — have developed a method, reported in Science, that enables them to see whether magnetic fields detected by a pair of atom-scale quantum sensors are correlated or not.
A heatmap of electron location in graphene shows that at the lower temperature (left panel), the electrons are more likely to bump into impurities (circles), with relatively fewer making it through the channel between impurities. At higher temperatures (right panel), electron flow shifts to being fluid-like. Fewer are stuck at the impurities and more flow through the channels. UNIVERSITY OF WISCONSIN–MADISON
Physicists at the University of Wisconsin–Madison directly measured, for the first time at nanometer resolution, the fluid-like flow of electrons in graphene. The results, which will appear in the journal Science on Feb. 17, have applications in developing new, low-resistance materials, where electrical transport would be more efficient.
Graphene, an atom-thick sheet of carbon arranged in a honeycomb pattern, is an especially pure electrical conductor, making it an ideal material to study electron flow with very low resistance. Here, researchers intentionally added impurities at known distances and found that electron flow changes from gas-like to fluid-like as temperatures rise.
Zach Krebs
“All conductive materials contain impurities and imperfections that block electron flow, which causes resistance. Historically, people have taken a low-resolution approach to identifying where resistance comes from,” says Zach Krebs, a physics graduate student at UW–Madison and co-lead author of the study. “In this study, we image how charge flows around an impurity and actually see how that impurity blocks current and causes resistance, which is something that hasn’t been done before to distinguish gas-like and fluid-like electron flow.
The researchers intentionally introduced obstacles in the graphene, spaced at controlled distances and then applied a current across the sheet. Using a technique called scanning tunneling potentiomentry (STP), they measured the voltage with nanometer resolution at all points on the graphene, producing a 2D map of the electron flow pattern.
No matter the obstacle spacing, the drop in voltage through the channel was much lower at higher temp (77 kelvins) vs lower temp (4 K), indicating lower resistance with more electrons passing through.
At temperatures near absolute zero, electrons in graphene behave like a gas: they diffuse in all directions and are more likely to hit obstacles than they are to interact with each other. Resistance is higher, and electron flow is relatively inefficient. At higher temperatures — 77 K, or minus 196 C — the fluid-like behavior of electron flow means they are interacting with each other more than they are hitting obstacles, flowing like water between two rocks in the middle of a stream. It is as if the electrons are communicating information about the obstacle to each other and diverting around the rocks.
“We did a quantitative analysis [of the voltage map] and found that at the higher temperature, the resistance is much lower in the channel. The electrons were flowing more freely and fluid-like,” Krebs says. “Graphene is so clean that we’re forcing the electrons to interact with each other before they interact with anything else, and that is crucial in getting them to behave like a fluid.”
Former UW–Madison graduate student Wyatt Behn is a co-first author on this study conducted in physics professor Victor Brar’s group. Funding was provided by the U.S. Department of Energy (DE-SC00020313), the Office of Naval Research (N00014-20-1-2356) and the National Science Foundation (DMR-1653661).
Celebrating International Day of Women and Girls in Science!
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February 11 is the International Day of Women and Girls in Science, and we’re more than happy to showcase some of our women physicists! We collected photos from women in the department, which you can see in a collage above. Some women also chose to share a bit about their research and/or what being a woman in science and woman in physics means to them. Those quotes are below.
Abby Warden, graduate student
My name is Abby Warden, a 5th year graduate student working in experimental high energy physics. My current work includes assembling Gas Electron Multiplier (GEM) chambers for electronics testing. GEMs are the newest muon sub detector that will be installed in the general particle detector, the Compact Muon Solenoid (CMS).
Dr. Camilla Galloni, Post-doc
Seen some muons? Working on the muon detector of the CMS experiment: GE11 installed in 2020 and successfully operated is the precursor of the GE21 and ME0 detectors now being constructed for the high luminosity LHC upgrade. This big “camera” takes “snapshots” of particles produced in high energy proton collisions and helps understand the fundamental interactions of nature.
Elise Chavez, graduate student
I’ve always been drawn to figuring out how the world works and it led me to my research and passion of learning how the universe works fundamentally at the subatomic level. I work with the Compact Muon Solenoid (CMS) that lies along the Large Hadron Colider (LHC) at CERN in Geneva. Being a woman in physics is a strange duality. There are times when I feel empowered and times I feel very small. It is strength, confidence, and understanding, but it is also alienating, discouraging, and conflicting. It has taught me a lot about people and myself. It gave me a passion to help and support women and minorities in physics because it is for everyone. Diversity is what helps discovery thrive and I hope one day that it can be solely an uplifting experience.
Dr. Charis Koraka, post-doc
Curiosity, along with kindness and compassion are some of the greatest human qualities and those that make societies prosper. The quest of understanding the laws and properties of the universe, has always been a driving source and what made me turn to physics. With perseverance, nothing is impossible!
Wren Vetens, graduate student
My experience as a woman in physics has been marked by perseverance, community, and solidarity. There is still much to be done to achieve equality within the field of physics but we can do our part by standing up for and supporting each other, especially supporting our juniors and those who are disabled, LGBTQ+, and/or POC. I chose physics because I am compelled to always look deeper when I have questions about the nature of life, the universe, and everything. The very same drive that led me to study Physics also led me to coming to terms with my own identity as a queer person, nonbinary person, and transgender woman. Suffice to say, I would not be who I am today without physics or without my gender, and really the two are simply manifestations of that drive. I am currently wrapping up my PhD in experimental particle physics as a part of the CMS collaboration and hoping to graduate this year. My research topic is a search for the unique signature of a long-lived composite particle made of six quarks, which could in principle be produced at the LHC and detected with the CMS detector.
Prof. Tulika Bose
I am an experimental particle physicist working on the CMS experiment at the Large Hadron Collider. I love being part of a large international physics collaboration looking to answer some of the most fundamental questions in physics today – what is responsible for dark matter ? What is the matter-antimatter asymmetry in our universe due to ? Are there new exotic particles out there ? We try to answer these questions using our detector, cutting-edge instrumentation, modern software (incorporating Artificial Intelligence/Machine Learning) and high-performance computing!
I study plasma astrophysics: how electric and magnetic fields interact with charged particles in astrophysical systems. This is an incredibly broad field and I enjoy all of it – how sunspots and solar flares work, how a single proton can acquire the energy of a hard hit tennis ball, and what the blotchy rings imaged around supermassive black holes are really telling us, to give just a few examples.
Having the time and capacity to study these things has been an incredible privilege. I’m grateful to my parents, who thought my mind was worth developing, and to my many wonderful teachers, colleagues, and students – I hope I do as well by them as they did and do by me. I’m grateful to the social infrastructure that gave me food, water, and shelter, cured my illnesses, and allowed me reproductive freedom of choice so I could become a person who lives her dreams.
Haddie McLean, outreach specialist
I love that my job allows me to bring physics to children, our next generation of scientists. I want to show them that physics is fun and it’s for everyone. I hope to inspire them to pursue a career in science.
Prof. Jim Lawler has passed away
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Professor Jim Lawler, the Arthur and Aurelia Schawlow Professor Emerit of Physics at UW–Madison, passed away January 29, 2023. He was 71.
Lawler was an atomic, molecular & optical physicist with a focus developing and applying laser spectroscopic techniques for determining accurate absolute atomic transition probabilities. He received his MS (’74) and PhD (’78) from this department, studying with now-professor emerit 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. He remained on the faculty until his retirement in May 2022.
Lawler served as department chair from 1994-1997. He also accumulated numerous awards and honors over his distinguished career. He was 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.
At the time of Lawler’s retirement, longtime collaborator Blair Savage, UW–Madison professor emeritus of astronomy, said of Lawler’s contributions to the field:
“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.”
During his tenure, 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.
Peter Weix remembered for his technical, mentoring, and outreach efforts in physics
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The Department of Physics mourns the loss of Peter Weix, who passed away January 13, 2023.
Peter began his career as an electronics technician in the U.S. Navy in 1984, where he served until 1990. Following his Navy service, he worked as an electronics technician for several companies in California before joining the SLAC National Accelerator Laboratory at Stanford. At SLAC he was a Senior Technician with involvement on both the Stanford Synchrotron Radiation Lightsource and what is now the Linac Coherent Light Source. He also served as a Safety Officer with special emphasis on earthquake safety. Peter and his wife, Sheri, relocated to Wisconsin in 2001 so that Peter could join the Plasma Physics Group at UW–Madison where he worked for more than 20 years and advanced to Senior Instrumentation Specialist.
Peter Weix at the 2020 The Wonders of Physics annual shows | DEPARTMENT OF PHYSICS
Peter’s work responsibilities at UW spanned a diverse range of technical operations for both the Madison Symmetric Torus (MST) and the Big Red Plasma Ball (BRB), two intermediate-scale experimental facilities for plasma physics research. He oversaw the mechanical and electrical aspects of the MST facility and its high-voltage pulsed-power systems, making sure the facility functioned as required, both technically and safely. He also oversaw all aspects of the high vacuum systems for both MST and BRB. There are many researchers, both in the local group and visiting collaborators, who relied on Peter’s efforts to make sure research projects stayed on track. Additionally, Peter directed key parts of large construction projects, such as the new programmable power supplies that replace MST’s passive capacitor-inductor circuits.
Peter’s involvement with plasma physics research included supervision of around 4-6 undergraduate students at any given time; he mentored an estimated more than 50 students during his time here. The students came from many areas of study, not just science and engineering, and rarely joined the group with the specific skills required to support research activities. Peter welcomed them into the department and provided them all with on-the-job training, teaching them skills and tricks of the trade to allow them to grow and become valuable members of the team.
In addition to his dedicated service to the plasma group, Peter recognized the importance and value of physics outreach. He became a vital member of The Wonders of Physics program for over twenty years. His involvement started when one of the participants was suddenly unavailable at the start of one of the public shows. Peter saved the day by learning on the fly how to operate the complicated audiovisual system. His performance under pressure was impressive, and he was then asked to be the coordinator and main announcer for the approximately 200 shows that followed. Through the years, he provided ideas, elaborate props, personnel, wisdom, and a calming influence on the entire cast. He spent countless hours volunteering his time to the program.
In recognition of his many contributions to the department and university, Peter was awarded the 2022-23 George Ott award for staff excellence, the only department-level staff award given. He will be recognized at the annual Awards and Scholarship banquet in May.
Profs. John Sarff and Clint Sprott contributed to this piece
Finding some wiggle room in semiconductor quantum computers
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Classical computers rarely make mistakes, thanks largely to the digital behavior of semiconductor transistors. They are either on or they’re off, corresponding to the ones and zeros of classical bits.
On the other hand, quantum bits, or qubits, can equal zero, one or an arbitrary mixture of the two, allowing quantum computers to solve certain calculations that exceed the capacity of any classical computer. One complication with qubits, however, is that they can occupy energy levels outside the computational one and zero. If those additional levels are too close to one or zero, errors are more likely to occur.
“In a classical computer, all the aspects of a transistor are super uniform,” says UW–Madison Distinguished Scientist Mark Friesen, an author on both papers. “Silicon qubits are in many ways like transistors, and we’ve gotten to the stage where we can control the qubit properties very well, except for one.”
That one property, known as the valley splitting, is the buffer between the computational one-zero energy levels and the additional energy levels, helping to reduce quantum computing errors.
In two papers published in Nature Communications in December, researchers from the University of Wisconsin–Madison, the University of New South Wales and TU-Delft showed that tweaking a qubit’s physical structure, known as a silicon quantum dot, creates sufficient valley splitting to reduce computing errors. The findings turn conventional wisdom on its head by showing that a less perfect silicon quantum dot can be beneficial.
Resolving very small objects that are close together is a frequent goal of scientists, making the microscope a crucial tool for research in many different fields from biology to materials science.
The resolution of even the best modern confocal microscopes — a common optical microscope popular in biology, medicine, and crystallography — is limited by an optical bound on how narrow a laser beam can be focused, known as the diffraction limit.
In a study recently published in the journal ACS Photonics, UW–Madison physics professor Shimon Kolkowitz and his group developed a method to image atomic-level defects in diamonds with super-resolution, reaching a spatial resolution fourteen times better than the diffraction limit achievable with their optics. And, because the technique uses a standard confocal microscope, this super-resolution should be available to any researchers that already have access to this common equipment.
Aedan Gardill
While methods to achieve super-resolution already exist, such as stimulated emission depletion microscopy (STED), nearly all of these methods either require the addition of special optics, which can be expensive and difficult to install, or specialized samples and extensive post processing of the data. The UW–Madison technique, which they call “super-resolution Airy disk microscopy” (SAM), avoids such barriers to entry.
“You can get this all for free with the existing setup that a lot of labs already have, and it performs almost just as well,” says Aedan Gardill, a graduate student in Kolkowitz’s group and lead author of the paper. “We were able to get resolution down to twenty nanometers, which is comparable with standard techniques using [STED].”
The ‘Airy disk’ in SAM refers to a key feature of light beams that gives rise to the diffraction limit but which the researchers turned to their advantage.
Confocal microscopes use laser beams of specific wavelengths to excite matter in a sample, causing that matter to emit light. On the microscopic scale, the laser beam does not create a solid circle of light on the sample in the same way a flashlight would. Rather, light hits the object in a series of light and dark rings called an Airy pattern. Within the dark rings, the matter receives no light, which means it cannot be detected by the microscope’s light sensors.
The novelty of the SAM technique is in its two laser beam pulses, one spatially offset from the other such that the overlapping Airy patterns can distinguish between two closely spaced objects.
In their paper, the research team studied nitrogen-vacancy (NV) centers in diamond crystal, which are regions in the crystal lattice where one of two neighboring carbon atoms is replaced by a nitrogen atom, and the other is left empty. NV centers are known to have two different charge states based on how many electrons are in the defect, one that fluoresces and one that remains dark when yellow light is applied to them.
To resolve two NV centers separated by a distance less than the diffraction limit of the microscope, the SAM procedure first shines green light on them, preparing both centers into their fluorescent charge state. Then, a red laser is applied, offset such that only one of the two NV centers is in the dark ring of the Airy pattern and thus is not affected by the beam. The NV center that does see the red light is switched to the dark state.
Super-resolution Airy disk Microscopy uses the Airy disk (red pattern) generated by diffraction from an objective lens aperture (gray cylinder) to localize and control an emitter (here a nitrogen vacancy center in diamond) below the diffraction limit. Emitter fluorescence is suppressed everywhere except in a very narrow ring (blue donut).
“It goes to another dark charge state where it does not interact with yellow light,” Gardill explains. “But the initial bright charge state does interact with yellow light and will emit light.”
Finally, when the yellow laser is applied, one NV center emits light while the other does not, effectively differentiating between the two neighboring sites. By repeating these steps iteratively over a grid, the researchers could reconstruct a full image of the two nearby NVs with spectacular resolution.
The idea for this technique came as a bit of a surprise while the team was studying charge properties of NV centers in 2020.
“We tried the combinations of red-green, green-red, red-red, green-green with those first two [laser] pulses, and the one that was green then red, we ended up seeing this ring,” Gardill recounts. “And Shimon was like, ‘The width of the ring is smaller than the size of [the confocal image of] the NV. That is super-resolution.’”
This method could find wide use in many different fields, including biology and chemistry where NV centers are used as nanoscale sensors of magnetic and electric fields and of temperature in compounds and organic material. NV centers have also been studied as candidates for quantum repeaters in quantum networks, and the research team has considered the feasibility of using the SAM technique to aid in this application. Currently, the SAM method has only been applied to NV centers in diamond crystal, and more research is needed to extend its use to different systems.
That all of this can be done with hardware that many labs across the world already have access to cannot be overstated. Gardill reiterates, “If they have a basic confocal microscope and don’t want to buy another super-resolution microscope, they can utilize this technique.”
This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award #DE-SC0020313.
Daniel Heimsoth is a second-year PhD student in Physics. This was his first news story for the department.
