Department of Physics
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Welcome, Prof. Britton Plourde!

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Britton Plourde (credit: Isabelle Delfosse, L&S)

Condensed matter experimentalist Britton Plourde received his bachelor’s in physics and music performance from the University of Michigan. He then went to grad school at UIUC, earning a PhD in physics and a master’s in music performance. He completed a postdoc at UC-Berkeley, then began as an assistant professor of physics at Syracuse University in 2005, moving up the ranks to full professor there. In Fall 2024, Plourde joined the UW–Madison physics department as a full professor. He is joining the department on a half-time appointment; for the other half, he will be working at Qolab, a quantum computing startup company based in Madison.

 Please give an overview of your research.

I work on superconducting quantum circuits. We make microfabricated superconducting circuits that have what are called Josephson tunnel junctions in them. And one of the biggest things we use these for is making qubits. We study all of the various physics related to how qubits work, what limits their performance, and ways to make them perform better so you could eventually build a practical, large-scale quantum computer. My research is similar to Robert McDermott’s and Roman Kuzmin’s.

What are the first one or two projects that you will have your group working on or continuing to work on when you arrive in Madison?

The company I’m working with, Qolab, is focused on building a quantum computer. My academic research lab at the university will be focused on fundamental physics related to operation of qubits, including the individual components of qubits like the Josephson junctions and to different processes that limit the performance of qubits. At the same time, the company is really focused on the technology of fabricating lots of qubits in a uniform, reproducible way and building them into a quantum computer.

In my group, a significant focus is going to be on understanding quasiparticles in superconducting qubits and how they impact the behavior of those qubits. Quasiparticles are electronic excitations above the superconducting ground state. The superconducting ground state is important because it doesn’t have any dissipation. But these quasiparticles are dissipative, and they can degrade the performance of a superconducting circuit. There are various things that can generate the quasiparticles, but one of them is radioactivity: background radiation from radioactive contaminants in the lab or from cosmic rays. My group is going to continue spending time on understanding the physics of those processes and coming up with ways to try to mitigate their effects to make qubits that are more immune to quasiparticles.

We’re also hoping to study quasiparticle physics in qubits for the completely opposite reason: instead of trying to mitigate the effects of quasiparticles to make better qubits, it’s to amplify the effects of quasiparticles to make better detectors, potentially to detect dark matter particles. Robert and I are co-principal investigators with some particle physics collaborators on two Department of Energy proposals for this work that we recently submitted. This work hasn’t been funded yet, but if it is, it is going to be a new and interesting research direction in both of our groups.

What attracted you to Madison and the university?

It’s a great department. I’ve known it for a long time because I collaborated with Robert almost as long as he’s been there. I’ve visited a lot over the years, and I like the area and the city. The university has made an impressive investment in quantum information science, and they’re a real leader in that area and have research strengths across multiple different qubit technologies, both experimentally and with a strong team of theorists working on different aspects of quantum information science and condensed matter. It’s really a powerhouse place, so I’m excited to join. University leadership has also been very supportive of the startup, they’re strongly encouraging of the entrepreneurial direction of faculty, and that’s not the case at a lot of other places.

What is your favorite element and/or elementary particle?

My favorite element has to be aluminum. That’s the superconductor we use the most. The same aluminum that you could use to wrap a hot dog at a baseball game to keep it warm, you can instead cool it down to below one degree Kelvin and it becomes a superconductor. And it makes great Josephson junctions for qubits.

What hobbies and interests do you have?

Well, I’m still a musician, I’m a flutist. I don’t really make money on it anymore, but I was a professional musician for a while. For the last three years of grad school, I had a job in a professional orchestra. I do still play occasionally, and I’ll have to see how much time I have when we get to Madison. My wife is a professional musician. She’s an oboist and she’ll be working part time in the School of Music developing a new monthly recital series.

UW–Madison joins new NSF-Simons AI Institute for the Sky

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This post is modified from the original news story from Northwestern University

A large multi-institutional collaboration— led by Northwestern University and including UW–Madison physics professors Keith Bechtol, Kyle Cranmer, and Moritz Münchmeyer — has received a $20 million grant to develop and apply new artificial intelligence (AI) tools to astrophysics research and deep space exploration.

Jointly funded by the National Science Foundation (NSF) and the Simons Foundation, the highly competitive grant will establish the NSF-Simons AI Institute for the Sky (SkAI, pronounced “sky”). SkAI is one of two National AI Research Institutes in Astronomy announced today. Northwestern astrophysicist Vicky Kalogera is principal investigator of the grant and will serve as the director of SkAI. Northwestern AI expert Aggelos Katsaggelos is a co-principal investigator of the grant.

The new institute will unite multidisciplinary researchers to develop innovative, trustworthy AI tools for astronomy, which will be used to pursue breakthrough discoveries by analyzing large astronomy datasets, transform physics-based simulations and more. With unprecedentedly large sky surveys poised to launch, including from the Vera C. Rubin Observatory in Chile, astronomers will require smarter, more efficient tools to accelerate the mining and interpretation of increasingly large datasets. SkAI will fulfill a crucial role in developing and refining these tools.

Read the full NU press release

Learn more about SkAI

HAWC detection of an ultra-high-energy gamma-ray bubble around a microquasar

This story is adapted from the HAWC Collaboration press release. Microquasars—compact regions surrounding a black hole with a mass several times that of its companion star—have long been recognized as powerful particle accelerators within our galaxy. The enormous jets spewing out of microquasars are thought to play an important role in the production of galactic cosmic rays, although [...]

Read the full article at: https://wipac.wisc.edu/hawc-detection-of-an-ultra-high-energy-gamma-ray-bubble-around-a-microquasar/

Welcome, Professor Ben Woods!

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Ben Woods

Condensed matter theorist Ben Woods joined the department as an assistant professor this fall. Originally from a small town in North Dakota, Woods studied physics at the University of North Dakota and earned a PhD in physics from West Virginia University. He first came to UW–Madison for a postdoc with Mark Friesen in 2021, and now moves into his faculty role.

Please give an overview of your research.

I primarily work in two main areas of condensed matter theory and quantum information science. The first area is the theory of semiconductor quantum dots, with applications towards building and operating quantum computers based on spin qubits. Quantum dots can be thought of as artificial atoms in which electrons are trapped and manipulated within a semiconductor, such as silicon, by metallic gates that sit on top of the semiconductor. An electron in the quantum dot forms the basis for a type of qubit called a spin qubit, where the quantum information is stored in the spin of the electron. I investigate how we can build higher quality spin qubits. One aspect of this is analyzing and designing single and two qubit gates such that their efficiency and noise resiliency can be improved. Another aspect is studying the materials and design of quantum dot devices to optimize certain properties, such as how the qubits respond to an external magnetic field. I am also interested in quantum dot arrays as a platform for quantum simulation. Here the idea is to engineer the interactions between the quantum dots to emulate a quantum system of interest.

The other area I work in is semiconductor-superconductor heterostructures. Here, you’re trying to combine desirable properties of both types of materials to create interesting devices that would otherwise be impossible. I study semiconductor-superconductor heterostructures that can give rise to exotic particles known as Majorana zero modes, which form the basis for topological qubits. These qubits are immune to certain error sources that more conventional types of qubits are not. I am trying to understand the effects of disorder on these heterostructures and develop new schemes in which Majorana zero modes can be realized.

What are one or two of the main projects your group will work on first?

One initial project will focus on designing a new qubit architecture for quantum dot spin qubits. In the most conventional type of spin qubit, you have a single electron spin that is manipulated by jiggling it with an electric field back and forth within a single quantum dot. It turns out, however, that these qubits can be manipulated more efficiently if you can hop electrons between multiple quantum dots. Specifically, I’ve devised new schemes involving three dots in a triangular geometry in which single-qubit gates can be performed quite efficiently. These ideas work in principle, but now it’s a matter of quantitatively studying how noise resilient the scheme is and how finely tuned the system parameters need to be for things to go as planned.

A second initial project is more towards quantum simulation using quantum dot arrays. The project will focus on studying magnetism in quantum dot arrays. In other words, asking how the spins of the quantum dot electrons organize due to their mutual interaction. One interesting wrinkle in these quantum dot arrays based on silicon is that there is a valley degree of freedom in addition to the usual spin degree of freedom. The project involves understanding the effects on the magnetic ordering due to this additional valley degree of freedom. Specifically, I am interested in how fluctuations in the valley degree of freedom from one dot to the next can impact magnetic ordering.

What attracted you to Madison and the university?

There were two main reasons. First, my wife had gotten a residency as an anesthesiologist at the UW hospital. So that was an obvious motivation. Second, one of my grad school advisors knew Mark Eriksson and Mark Friesen and thought it’d be a natural fit for me to work with them as a postdoc. Since moving here, my family has enjoyed Madison, and I really like the physics department. The people are very friendly and collaborative. I am incredibly happy to be able to stay in Madison and at the UW physics department.

What is your favorite element and/ or elementary particle?

It has to be silicon, right? It’s the material I think about every day. And the world economy is largely based on stuff made with silicon. So that’s pretty cool?

What hobbies and interests do you have?

I like to play guitar, read, watch sports, and spend time with my family and friends. I have two kids, three years and six months old, who I like to spend most of my free time on.

Baha Balantekin wins 2025 APS Bethe Prize

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Baha Balantekin

Congrats to Prof. Baha Balantekin on winning the American Physical Society’s 2025 Hans A. Bethe prize!

The Bethe prize is awarded to recognize outstanding work in theory, experiment or observation in the areas of astrophysics, nuclear physics, nuclear astrophysics, or closely related fields. Balantekin won “for seminal contributions to neutrino physics and astrophysics — especially the neutrino flavor transformation problem — both for solar neutrinos and the nonlinear supernova environment.”

Balantekin works at the intersection of particle physics, nuclear physics, and astrophysics. For much of his career, he has studied theoretical aspects of neutrino transport originating in the Sun, supernovae, or neutron star mergers.

“The concepts (I brought to the field) were marrying neutrino physics with many-body physics,” Balantekin says. “Of course, incorporating many-body aspects is common in condensed matter and nuclear physics, but it’s not as common in environments studied in astrophysics.”

Several fundamental astrophysical processes produce neutrinos as byproducts, and scientists have been studying neutrino origins and patterns for decades. Detecting the Sun’s neutrinos can reveal insights into its nuclear reactions, for example, and detecting neutrinos from core collapse supernovae can reveal insights into the early universe.

Balantekin’s early research was on the theory of neutrino transport from the Sun. He has also been studying core collapse supernovae, the result of a star running out of nuclear fuel. During collapse, a very hot star cools very quickly, emitting neutrinos on the order of 10^58.

“A number of that magnitude means you can no longer ignore the neutrino-neutrino interactions,” Balantekin says. “And then it becomes a very interesting many-body problem, where you have two-body interactions between neutrinos, and the propagation, and then it becomes a very complex problem.”

black and white group photo from 1995. There are 7 men featured
Balantekin and department collaborators in 1995. Balantekin is seated, right. Seated next to him is former PhD student Alan DeWeerd. Standing row, L-R: Franco Ruggeri, John Beacom, Jonathan Fetter, late physics professor Kirk McVoy, and William Friedman.

To describe this problem, has more recently begun using techniques from quantum information science to study entanglement of neutrinos with each other and to look at the signatures of such interactions and how they might contribute to heavy element formation.

The Bethe Prize was awarded solely to Balantekin, but he says he would not have won it without his collaborators over the years.

“You don’t do work in a vacuum,” Balantekin says. “I’ve worked with a lot of very talented young people. I would like to acknowledge first not only my graduate students at Wisconsin, but also the Fellows who came from the N3AS Physics Frontier Center we have. And the people I collaborate with around the world. We also have colleagues here in the department like Sue Coppersmith and Mark Saffman who contributed many ideas.”

The Bethe prize consists of $10,000 and a certificate citing the contributions made by the recipient. It is presented annually.

Britton Plourde elected Fellow of the American Physical Society

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Britton Plourde (credit: Syracuse University)

Congratulations to Prof. Britton Plourde for being elected a Fellow of the American Physical Society!

Plourde was elected “For important contributions to the physics and operation of superconducting qubits, including the development of techniques for scalable qubit control and readout, and investigations of decoherence from vortices and nonequilibrium quasiparticles.” He was nominated by the Division of Quantum Information Fellowship.

APS Fellowship is a distinct honor signifying recognition by one’s professional peers for outstanding contributions to physics. Each year, no more than one half of one percent of the Society’s membership is recognized by this honor.

See the full list of 2024 honorees at the APS Fellows archive.