Department of Physics
Research, teaching and outreach in Physics at UW–Madison

News Archives

Three undergraduate students awarded Hilldale Fellowships

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Congratulations to the three physics undergraduate research students who earned Hilldale fellowships for 2020-21! They are:

  • Owen Rafferty, in Robert McDermott’s group
  • Yanlin Wu, in Peter Timbie’s group
  • Yan Qian, in Sau Lan Wu’s group

The Hilldale Undergraduate/Faculty Research Fellowship provides research training and support to undergraduates at UW–Madison. Students have the opportunity to undertake their own research project in collaboration with UW–Madison faculty or research/instructional academic staff. Approximately 97 – 100 Hilldale awards are available each year.

Vandenbroucke group plays instrumental role in proving viability of innovative gamma-ray telescope

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Scientists in the Cherenkov Telescope Array (CTA) consortium have detected gamma rays from the Crab Nebula using the prototype Schwarzschild-Couder Telescope (pSCT), proving the viability of the novel telescope design for use in gamma-ray astrophysics. The announcement was made today by Justin Vandenbroucke, associate professor at the University of Wisconsin–Madison, on behalf of the CTA Consortium at the virtual 236th meeting of the American Astronomical Society (AAS).

“The Crab Nebula is the brightest steady source of TeV, or very high-energy, gamma rays in the sky, so detecting it is an excellent way of proving the pSCT technology,” says Vandenbroucke, who is also affiliated with the Wisconsin IceCube Particle Astrophysics Center (WIPAC) at UW–Madison. “Very high-energy gamma rays are the highest energy photons in the universe and can unveil the physics of extreme objects, including black holes and possibly dark matter.”

Vandenbroucke is coleader of a team made up of WIPAC scientists and other collaborators that developed and operate a critical part of the telescope: its high-speed camera. Vandenbroucke has worked on the design, construction, and integration of the camera since 2009.

Read the full story on the WIPAC website. The WIPAC story was adapted from a CTA press release.

Keith Bechtol, Rob Morgan win UW’s Cool Science Image contest

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pieced-together photos of space with a helix nebula the most visibleCongrats to Prof. Keith Bechtol and graduate student Rob Morgan for their winning entry in the UW–Madison Cool Science Images contest! Their winning entry — one of 12 selected out of 101 entries — earns them a large-format print which initially will be displayed in a gallery at the McPherson Eye Research Institute’s gallery in the WIMR building.

This snapshot of the sky contains thousands of distant galaxies, each containing billions of stars. Bechtol and Morgan were looking for the flash of the explosion of a single star, the potential source of a sub-atomic particle called a neutrino, spotted zipping through the Earth by the IceCube Neutrino Observatory at the South Pole. The distant galaxies, swirling billions of light years away, are all the harder to see because of nearby objects, like the pictured Helix Nebula. The image was captured with a Dark Energy Camera and Victor M. Blanco telescope.

To learn more about the Cool Science Images contest and to view the other winning images, please visit https://news.wisc.edu/the-winners-cool-science-images-2020/.

 

Mark Eriksson earns WARF named professorship

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Mark Eriksson has been named the John Bardeen Professor of Physics, through the Wisconsin Alumni Research Foundation (WARF) named professorship program.

The WARF named professorship program provides recognition for distinguished research contributions of the UW–Madison faculty. The awards are intended to honor those 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.

profile photo of Mark Eriksson
Mark Eriksson

Eriksson joined the UW–Madison physics faculty in 1999. His research has focused on quantum computing, semiconductor quantum dots, and nanoscience. He currently leads a multi-university team focused on the development of spin qubits in gate-defined silicon quantum dots. A goal of this work is to enable quantum computers, which manipulate information coherently, to be built using many of the materials and fabrication methods that are the foundation of modern, classical integrated circuits.

“If you look back at my work here over the last, it’ll be 21 years in August, it’s almost all been collaborative, and I’ve really enjoyed the people I’ve worked with,” Eriksson says. “Going into the future, those collaborations are going to continue, of course. We have a real opportunity to see what semiconductor fabrication technology can do for qubits and quantum computing — how can we make really high-quality, silicon qubits in a way that leverages and makes use of the same technology that people use to make classical computer chips?”

a group of 7 people
Members of the Eriksson Group at a conference in Spain in Fall 2019.

Eriksson’s past and present UW–Madison collaborators include, in addition to many students and postdocs, physics professors Victor Brar, Sue Coppersmith, Bob Joynt, Shimon Kolkowitz, and Robert McDermott; physics senior scientist Mark Friesen; and materials science and engineering professor Max Lagally and scientist Don Savage.

The WARF program asks recipients to choose the name of their professorship. Eriksson, who graduated with a B.S. in physics and mathematics from UW–Madison in 1992, chose fellow alum John Bardeen — a scientist who has the unique honor of being the only person to receive the Nobel Prize in Physics twice.

“Bardeen was one of the inventors of the transistor, and I work with semiconductor qubits which are very similar to transistors in many ways,” Eriksson explains. “It seemed appropriate to choose him, because he was an alum of the university, he’s a Madison native, and he was co-inventor of the transistor.”

Eriksson was one of 11 UW­–Madison faculty awarded WARF named professorships this year. The honor comes with $100,000 in research funding over five years.

“Prof. Mark Eriksson is a world-leading expert in the development of quantum information systems using solid-state quantum dot qubits,” says Sridhara Dasu, physics department chair. “Recognition of his successes in research and his contribution to the training of researchers in this increasingly promising area of quantum information, through the awarding of WARF professorship, is much deserved.”

Profs Eriksson, McDermott, Vandenbroucke awarded UW2020s

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Twelve projects have been chosen for Round 6 of the UW2020: WARF Discovery Initiative, including three from faculty in the Department of Physics (Mark Eriksson, Robert McDermott, and Justin Vandenbroucke). These projects were among 92 proposals submitted from across campus. The initiative is funded by the Office of the Vice Chancellor for Research and Graduate Education and the Wisconsin Alumni Research Foundation.

The projects were reviewed by faculty across the university. The UW2020 Council, a group of 17 faculty from all divisions of the university, evaluated the merits of each project based on the reviews and their potential for making significant contributions to their field of study.

The goal of UW2020 is to stimulate and support cutting-edge, highly innovative and groundbreaking research at UW–Madison and to support acquisition of shared instruments or equipment that will foster significant advances in research.

Acquisition of a cryogen-free Physical Properties Measurement System (PPMS) for characterization of quantum materials and devices

The project addresses a barrier for UW–Madison researchers in measuring electronic, magnetic, and thermal properties of quantum materials at low temperatures, namely the increasing high costs of cryogens (liquid helium) and lack of a convenient means to perform these measurements in a shared facility. Low-temperature electronic, magnetic, and thermal properties of materials are crucial for fundamental materials discovery and for applications in quantum information, nonvolatile memory, and energy conversion devices.

This project will acquire a cryogen-free Physical Properties Measurement System (PPMS) and house it as a shared-user facility instrument within the Wisconsin Centers for Nanotechnology (CNT). This instrument would be open for all UW–Madison users.

Currently, these measurements depend on external collaborations or low-temperature setups in PI labs which either consume large amounts of cryogens or require time-consuming reconfigurations from experiment to experiment. Having a cryogen-free PPMS would allow researchers to spend less time and money in setting up experiments, potentially freeing up resources for scientific investigations that include new superconducting and topological material discoveries and characterizations of materials for advanced microelectronics and magnetic memory systems.

PRINCIPAL INVESTIGATOR
Jason Kawasaki, assistant professor of materials science and engineering

CO-PRINCIPAL INVESTIGATOR
Jerry Hunter, director of the Wisconsin Centers for Nanotechnology

CO-INVESTIGATOR
Paul Voyles, professor of materials science and engineering and MRSEC Director

Song Jin, professor of chemistry

Mark Eriksson, professor of physics

Thomas Kuech, professor of chemical and biological engineering

Daniel Rhodes, assistant professor of materials science and engineering

Chang-Beom Eom, professor of materials science and engineering

Paul Evans, professor of materials science and engineering

Michael Arnold, professor of materials science and engineering

Dakotah Thompson, assistant professor of mechanical engineering

Cracking the structure of ice: establishing a cryogenic electron backscatter diffraction and Raman capability at UW–Madison

The structure and physical properties of ice determine the behavior of glaciers, ice sheets, and polar ice caps (both terrestrial and extraterrestrial). Moreover, ice is of interest because of its unique light transmission properties, which are currently being harnessed by one of the world’s largest astrophysical experiments through the UW–led IceCube collaboration.

This project will develop the capability to perform scanning electron microscopy (SEM) of water and CO2 ice in the UW–Madison Geoscience Department, focusing on electron backscatter diffraction (EBSD) analysis for ice microstructure and Raman spectroscopy for ice composition. EBSD of ice is an extremely rare analytical capability worldwide.

Having this highly specialized type of analysis capability for ice will enable advances in glaciology, climate science, physics, materials science and planetary science. This technology can accelerate research on glacial sliding and ice deformation, and inform long-standing questions about the transformation of air bubbles to clathrates in glacial ice and their potential as archives of Earth’s past atmosphere. In addition, understanding the structure of ice is critical, for example, to accurate measurement of cosmic ray interactions in the IceCube Neutrino Observatory.

As the only lab in the U.S. offering combined ice EBSD analysis and ice Raman analysis, UW–Madison will establish itself as a nexus for cryosphere research, attracting many collaborations from outside UW–Madison.

PRINCIPAL INVESTIGATOR
Chloe Bonamici, assistant professor of geoscience

CO-PRINCIPAL INVESTIGATORS
Lucas Zoet, assistant professor of geoscience

Shaun Marcott, associate professor of geoscience

Justin Vandenbroucke, associate professor of physics/WIPAC

John Fournelle, senior scientist of geoscience

CO-INVESTIGATORS
Pavana Prabhakar, assistant professor of civil and environmental engineering

Richard Hartel, professor of food engineering

Hiroki Sone, assistant professor of geological engineering

Interdisciplinary engineering of quantum information systems

This project represents a synergistic effort toward engineering practical quantum information systems (QIS). The research unites the experimental superconducting and semiconducting qubit teams on campus with advanced materials characterization and microwave engineering expertise to uncover the underlying sources of decoherence that limit qubit performance and develop next-generation quantum devices for scalable quantum computing and quantum sensing. This effort will build new interdisciplinary connections that nourish the quantum ecosystem at UW–Madison, cutting across departmental and disciplinary lines.

The potential of QIS has been recognized recently by the $1.4 billion federal National Quantum Initiative, and the newly formed Wisconsin Quantum Institute at UW is home to world-leading efforts in the physics of QIS. This project is a next step in expanding these directions to incorporate the engineering effort necessary to develop practical systems capable of solving real-world problems.

PRINCIPAL INVESTIGATOR
Robert McDermott, professor of physics

CO-PRINCIPAL INVESTIGATORS
Mark Eriksson, professor of physics

Susan Hagness, professor of electrical and computer engineering

Paul Voyles, professor of materials science and engineering

Kangwook Lee, professor of electrical and computer engineering

Physics Department featured in UW article on virtual lab course instruction

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It’s one thing to have to move a lecture course online, but lab courses — where students learn by doing — is an entirely different story. University Communications spoke to instructors in Physics, including Prof. Deniz Yavuz and Dr. Jim Reardon, about the transition to online lab instruction.  

Read the full story

Manipulating the magnetic response to light in natural materials

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When light moves from one material into another, it bends — like how a partially submerged object appears distorted under water when viewed from above. What if, instead of bending, a material could change the light so much that the material was no longer visible at all?

In a study published in Physical Review A, University of Wisconsin­–Madison researchers have shown for the first time that a similar response can be obtained and manipulated in naturally-occurring materials. The findings have implications from the development of “perfect” lenses for improved microscopy to Harry Potter-esque invisibility cloaks.

Visible light is made of both magnetic and electric fields, and the refractive index of a material — how much it bends the light — is determined by how the material interacts with those two fields. Nearly all materials we encounter in everyday life, though, interact entirely with light’s electric field.

profile photo of Zach Buckholtz
Zach Buckholtz

Researchers have spent the past two decades developing artificial materials that more strongly interact with light’s magnetic field by manipulating the refractive index. With a strong enough response, the material could eventually have a negative refractive index, leading to unique optical properties. However, the response in synthetic materials is limited by the size of their repeating units. A naturally-occurring crystal that has much smaller unit cells is likely a better choice.

“Part of producing a negative refractive index is that the material needs to have a strong response to both electric and magnetic fields, so the big challenge is getting that magnetic response in natural materials,” explains Zach Buckholtz, a graduate student in UW–Madison physics professor Deniz Yavuz’s group and lead author of the study. “A few years ago, we published a paper showing that the crystal we’re working with has a magnetic response, and in this study, we were able to manipulate the response.”

The natural material Buckholtz is working with is a silicon-based crystal, which in general is optically ordinary, except that it has been “doped” with the rare earth metal Europium. Rare earth metals are unique in that they contain an abundance of electrons in the atoms’ outer energy shells. Those electrons can then work together to create a bigger magnetic response, but only if they are all in tune with each other.

“If you have some magnetic response and a much larger electric response to light, you can connect those two responses,” Buckholtz says. “To get to a negative refractive index from there, you have to set up coherences between the energy levels, meaning you have to make sure all those energy levels are oscillating together.”

the apparatus hosting the rare earth metal doped crystal glows orange, and the background of the photo has a green fluorescence hue from the input laser
The experimental setup in the Yavuz lab. The orange glow is from the fluorescing crystal, with the green laser providing the green hue outside the chamber.

To show they can manipulate the magnetic response, Buckholtz and Yavuz did two things. First, because the crystal is a mix of ions with slightly different electron responses, they needed to set up their experimental system to select for one class of ion. This uniformity allows for a cleaner interpretation of the results.

“We send a laser into the crystal, and then measure how much of the light is transmitted. But because the crystal isn’t perfect, instead of seeing a narrow peak for the transitions, you’ll see a really broad transition,” Buckholtz explains. “So, we do this procedure known as spectral hole burning to clear out the ions we don’t want and then we’ll be left with just one transition, which is necessary to move on to experiments that involve coherence.”

Next, they wanted to show if they could increase the magnetic response. To do so, they needed to take those selected ions, put them in coherence, and then measure the response compared to ions not in coherence. In these experiments, they shined one (a probe beam) or two (probe and coupling beam) wavelengths of laser at the ions. Both lasers excite electrons in the ions to a higher-energy state, and the scientists can again measure how might light is transmitted through the crystal as a readout of the electron transitions.

“With just the probe beam, we see just the normal transition, and that’s what we did in our previous study. But with the coupling beam added in, it connects and adds another transition state in there,” Buckholtz says. “If those states are in coherence, they cancel each other out, and we see that effect as a peak in transmitted light, which means the index of refraction is going toward zero.”

Buckholtz notes that the magnetic response they see is not yet large enough to produce the materials with interesting new optical properties they are hoping for. Still, he says, this work provides a path forward to continue manipulations to improve the response, such as investigating different rare earth metals.

“We have a magnetic response, we can set up coherence, and we can manipulate the response,” Buckholtz says. “Now, we want to increase the scale of the response to with a goal of eventually making the refractive index below zero.”

Saffman group part of team awarded $7.4M grant to apply quantum computers to real-world problems

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Wisconsin Quantum Institute director and professor of physics Mark Saffman and his research group are part of a team that will attempt to make quantum computing hardware more applicable to real-world problems.

The up to $7.4 million Defense Advanced Research Projects Agency (DARPA) funding is through the ONISQ program — Optimization with Noisy Intermediate-Scale Quantum devices. ColdQuanta is the primary recipient of the funding, and Saffman’s group at the University of Wisconsin–Madison, along with a national lab and other universities, are partners.

“We’re in this era of development of quantum computing hardware that has been termed NISQ, and that’s because we don’t have error correction running on our quantum hardware,” says Saffman, who is also a UW–Madison professor of physics and chief scientist for quantum information at ColdQuanta. “The question is, can we do anything useful with this? Because the outlook for having a real error-corrected quantum computer that you could run very long calculations still seems to be a long way away, but we have these NISQ machines today, and they’re getting better all the time.”

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