Welcome, assistant professor Ilya Esterlis

profile photo of Ilya Esterlis
Ilya Esterlis

When Lake Mendota freezes over in the winter and thaws in the spring, those water/ice phase transitions might seem mundane. But, says new assistant professor of physics Ilya Esterlis, interesting things happen during phase transitions, and commonalities exist between phase transitions of any matter.

“That’s very surprising and strange sounding, but it turns out that there’s a very general framework in which to understand [these commonalities],” Esterlis says. “It’s this notion of universality, and by studying phase transitions you’re simultaneously studying a very broad class of materials.”

Esterlis, a condensed matter theorist whose research focuses on materials and phase transitions, joins the department January 1, 2023. He is currently a postdoctoral fellow at Harvard, and joined us for a virtual interview earlier this fall.

Can you please give an overview of your research?

I am a condensed matter theorist, so I study materials, and in particular I try to classify different phases of matter and the phase transitions between those phases of matter. I’m mostly interested in electronic systems, where you have a large macroscopic number of interacting electrons and are trying to understand the kind of phenomena that can emerge when you have that large number of degrees of freedom interacting with one another. And a lot of these things are motivated by experiments — not all of them. There are some more academic questions that I’m interested in investigating and they’re a bit more formal. But I’m also motivated by interesting things that are happening in the lab. Part of my work is not only trying to characterize and understand phases of matter, but also trying to propose ways that different phases could be detected experimentally, how they would manifest themselves in different experimental signatures.

I’m also interested in superconductivity. My PhD work focused a lot on trying to understand the optimal conditions for making superconductors — if you could have every knob at your disposal, what would you do to optimize them? Optimize in this case means: make superconductors that exist at as high of a temperature as possible. Superconductivity is typically a low temperature phenomenon, so there’s a holy grail in condensed matter physics trying to make higher temperature superconductors. Part of my work has been organized around trying to understand what would be even in principle the optimal route towards achieving higher temperature superconductors.

Once you’re in Madison, what are one or two research projects you and your group will focus on?

I will focus a good amount of my research efforts on studying superconductivity, continuing this line of investigation into what the optimal conditions for superconductors are. If you had all the freedom in the world, how would you build the best superconductor that exists to high temperatures and under normal laboratory conditions? Not under extreme, unrealistic conditions but in an everyday parameter regime. And that involves understanding the superconducting state itself. Superconductors are a phase of matter that is distinct from, say, a metal, which is also a good conductor but not a superconductor. But oftentimes to understand superconductors better, one has to understand the state from which they came. That is to say, you take a metal and you cool it down to low temperatures and it goes from being a good conductor to a superconductor. To understand that superconductor, it’s often helpful to understand the metal from which it came at higher temperature. And sometimes those metals can be conventional, like copper wires, but sometimes they can be very unconventional metals and strange for various reasons. One open question is: what is the interplay between superconductivity and unusual metals? If you take a high temperature unusual metal, what is the kind of superconductor that it turns into at lower temperature? And unusual in this context means that it has some properties that are not typical to conventional metals. For instance, there’s predictions for how resistance changes with temperature in a conventional metal but unusual metals have rather different resistance behaviors.

What is your favorite element and/or elementary particle?

Helium is remarkable in that it has a number of unusual properties. For instance, if you cool it down to zero temperature it does not crystallize, it remains a liquid. That’s solely due to quantum mechanics, which is kind of an incredible thing. If you do make it crystallize by applying pressure, then that solid itself also has very interesting properties.

And my favorite elementary particle is the anyon. It’s not elementary, say, in the sense of electrons or quarks. But it’s this really remarkable thing that happens in condensed matter systems where if you take a macroscopic number of electrons and you subject them to a very large magnetic field, then a remarkable thing happens where the behavior of the system, as viewed kind of on macroscopic scales, does not look like the behavior of electrons, it really looks like the behavior of particles called anyons that have fractional electric charge. So they are elementary in condensed matter physics.

What hobbies and interests do you have? 

I really love to play music, guitar specifically. And I have two small kids, two daughters, and I just like hanging out with them.

Welcome, Roman Kuzmin, the Dunson Cheng Assistant Professor of Physics

profile photo of Roman Kuzmin
Roman Kuzmin

In the modern, cutting-edge field of quantum computing, it can be a bit puzzling to hear a researcher relate their work to low-tech slide rules. Yet that is exactly the analogy that Roman Kuzmin uses to describe one of his research goals, creating quantum simulators to model various materials. He also studies superconducting qubits and ways to increase coherence in this class of quantum computer.

Kuzmin, a quantum information and condensed matter scientist, will join the department as an the Dunson Cheng Assistant Professor of Physics on January 1. He is currently a research scientist at the University of Maryland’s Joint Quantum Institute in College Park, Md, and recently joined us for an interview.

Can you please give an overview of your research?

My main fields are quantum information and condensed matter physics. For example, one of my interests is to solve complicated condensed matter problems using new techniques and materials which quantum information science developed. Also, it works in the other direction. I am also trying to improve materials which are used in quantum information. I work in the subfield of superconducting circuits. There are several different directions in quantum information, and the physics department at Wisconsin has many of them already, so I will complement work in the department.

Once you’re in Madison and your lab is up and running, what are the first big one or two big things you want to really focus your energy on

One is in quantum information and quantum computing. So, qubits are artificial atoms or building blocks of a quantum computer. I’m simplifying it, of course, but there are environments which try to destroy coherence. In order to scale up those qubits and make quantum computers larger and larger — because that’s what you need eventually to solve anything, to do something useful with it — you need to mitigate decoherence processes which basically prevent qubits from working long enough. So, I will look at the sources of those decoherence processes and try to make qubits live longer and be longer coherent.

A second project is more on the condensed matter part. I will build very large circuits out of those Josephson junctions, inductors and capacitors, and such large circuits behave like some many-body objects. It creates a problem which is very hard to solve because it contains many parts, and these parts interact with each other such that the problem is much more complicated than just the sum of those parts.

What are some applications of your work?

Of course this work is interesting for developing theory and understanding our world. But the application, for example for the many-body system I just described, it’s called the quantum impurity. One of my goals is to use this to create a simulator which can potentially model some useful material. It’s like if you have a quantum computer, you can write a program and it will solve something for you. A slide rule is a physical device that allows you to do complicated, logarithmic calculations, but it’s designed to do only this one calculation. I’m creating kind of a quantum slide rule.

What is your favorite element and/or elementary particle? 

So, I have my favorite circuit element: Josephson junction. (editor’s note: the question did not specify atomic element, so we appreciate this clever answer!). And for elementary particle, the photon, especially microwave photons, because that’s what I use in these circuits to do simulations. They’re very versatile and they’re just cool.

What hobbies and interests do you have?

I like reading, travelling, and juggling.

New technique reveals changing shapes of magnetic noise in space and time

This article was originally published by Princeton Engineering

Electromagnetic noise poses a major problem for communications, prompting wireless carriers to invest heavily in technologies to overcome it. But for a team of scientists exploring the atomic realm, measuring tiny fluctuations in noise could hold the key to discovery.

“Noise is usually thought of as a nuisance, but physicists can learn many things by studying noise,” said Nathalie de Leon, an associate professor of electrical and computer engineering at Princeton University. “By measuring the noise in a material, they can learn its composition, its temperature, how electrons flow and interact with one another, and how spins order to form magnets. It is generally difficult to measure anything about how the noise changes in space or time.”

Using specially designed diamonds, a team of researchers at Princeton and the University of Wisconsin–Madison have developed a technique to measure noise in a material by studying correlations, and they can use this information to learn the spatial structure and time-varying nature of the noise. This technique, which relies on tracking tiny fluctuations in magnetic fields, represents a stark improvement over previous methods that averaged many separate measurements.

a small square chip sits on a metallic microscope stand with green laser light bouncing off of it in places
Using specially designed diamonds with nitrogen-vacancy centers, researchers at Princeton University and the University of Wisconsin-Madison have developed a technique to measure noise in a material by studying correlations, and they can use this information to learn the spatial structure and time-varying nature of the noise. In this image, a diamond with near-surface nitrogen-vacancy centers is illuminated by green laser light from a microscope objective lens | Photo by David Kelly Crow and provided by Princeton University

De Leon is a leader in the fabrication and use of highly controlled diamond structures called nitrogen-vacancy (NV) centers. These NV centers are modifications to a diamond’s lattice of carbon atoms in which a carbon is replaced by a nitrogen atom, and adjacent to it is an empty space, or vacancy, in the molecular structure. Diamonds with NV centers are one of the few tools that can measure changes in magnetic fields at the scale and speed needed for critical experiments in quantum technology and condensed matter physics.

While a single NV center allowed scientists to take detailed readings of magnetic fields, it was only when de Leon’s team worked out a method to harness multiple NV centers simultaneously that they were able to measure the spatial structure of noise in a material. This opens the door to understanding the properties of materials with bizarre quantum behaviors that until now have been analyzed only theoretically, said de Leon, the senior author of a paper describing the technique published online Dec. 22 in the journal Science.

“It’s a fundamentally new technique,” said de Leon. “It’s been clear from a theoretical perspective that it would be very powerful to be able to do this. The audience that I think is most excited about this work is condensed matter theorists, now that there’s this whole world of phenomena they might be able to characterize in a different way.”

One of these phenomena is a quantum spin liquid, a material first explored in theories nearly 50 years ago that has been difficult to characterize experimentally. In a quantum spin liquid, electrons are constantly in flux, in contrast to the solid-state stability that characterizes a typical magnetic material when cooled to a certain temperature.

profile photo of Shimon Kolkowitz
Shimon Kolkowitz

“The challenging thing about a quantum spin liquid is that by definition there’s no static magnetic ordering, so you can’t just map out a magnetic field” the way you would with another type of material, said de Leon. “Until now there’s been essentially no way to directly measure these two-point magnetic field correlators, and what people have instead been doing is trying to find complicated proxies for that measurement.”

By simultaneously measuring magnetic fields at multiple points with diamond sensors, researchers can detect how electrons and their spins are moving across space and time in a material. In developing the new method, the team applied calibrated laser pulses to a diamond containing NV centers, and then detected two spikes of photon counts from a pair of NV centers — a readout of the electron spins at each center at the same point in time. Previous techniques would have taken an average of these measurements, discarding valuable information and making it impossible to distinguish the intrinsic noise of the diamond and its environment from the magnetic field signals generated by a material of interest.

“One of those two spikes is a signal we’re applying, the other is a spike from the local environment, and there’s no way to tell the difference,” said study coauthor Shimon Kolkowitz, an associate professor of physics at the University of Wisconsin–Madison. “But when we look at the correlations, the one that is correlated is from the signal we’re applying and the other is not. And we can measure that, which is something people couldn’t measure before.”

Kolkowitz and de Leon met as Ph.D. students at Harvard University, and have been in touch frequently since then. Their research collaboration arose early in the COVID-19 pandemic, when laboratory research slowed, but long-distance collaboration became more attractive as most interactions took place over Zoom, said de Leon.

Jared Rovny, the study’s lead author and a postdoctoral research associate in de Leon’s group, led both the theoretical and experimental work on the new method. Contributions by Kolkowitz and his team were critical to designing the experiments and understanding the data, said de Leon. The paper’s coauthors also included Ahmed Abdalla and Laura Futamura, who conducted summer research with de Leon’s team in 2021 and 2022, respectively, as interns in the Quantum Undergraduate Research at IBM and Princeton (QURIP) program, which de Leon cofounded in 2019.

The article, Nanoscale covariance magnetometry with diamond quantum sensors, was published online Dec. 22 in Science. Other coauthors were Zhiyang Yuan, a Ph.D. student at Princeton; Mattias Fitzpatrick, who earned a Ph.D. at Princeton in 2019 and was a postdoctoral research fellow in de Leon’s group (now an assistant professor at Dartmouth’s Thayer School of Engineering); and Carter Fox and Matthew Carl Cambria of the University of Wisconsin–Madison. Support for the research was provided in part by the U.S. National Science Foundation, the U.S. Department of Energy, the Princeton Catalysis Initiative and the Princeton Quantum Initiative.

The University of Wisconsin–Madison’s Department of Physics contributed to this article.

Experimental condensed matter physics professor Marshall Onellion has passed away

Marshall Onellion

UW–Madison physics professor Marshall Onellion passed away November 20, 2022. He was 72.

After completing his BS in mathematics and physics at West Virginia University in 1972, Onellion served in the U.S. Air Force until he was honorably discharged with the rank of Captain in 1979. He then began graduate studies in physics at Rice University, earning his PhD in 1984 before completing postdoctoral research at the University of Texas, Austin and Harvard University. Onellion joined the UW–Madison physics faculty as an assistant professor in 1987.

A condensed matter experimentalist, Onellion established a vigorous research program that primarily utilized the Aladdin ring at the UW-Madison Synchrotron Radiation Center (SRC) located in Stoughton, WI, for innovative studies of correlated electron materials of various types, including high-temperature superconductors, thin films, and magnetic multi-layers. His workhorse experimental tool was angle-resolved photoemission that was ideally suited to the stable and bright UV SRC synchrotron source.

Over the course of the next 15 years, his work was prolific. He published over 180 peer-reviewed articles, was a thesis advisor to many graduate and undergraduate students, and trained several postdoctoral researchers.

Onellion garnered numerous awards over his career, including being named a Hertz Fellow in graduate school and earning a National Science Foundation Presidential Young Investigator award in 1987. In 1996, he was named a UW–Madison Vilas Research Associate.

For many years Marshall actively volunteered to work with science students in area high schools, primarily Stoughton High School.  In recognition of this outstanding service, in 2000 Marshall received a State of Wisconsin Certificate of Commendation for Public Service from Governor Tommy Thompson.

Special thanks to Prof. Thad Walker and Robert Sundling for contributing to this piece

Please visit the department’s tribute page to Marshall Onellion to submit and/or read stories from Marshall’s colleagues.

Plasma astrophysicist and emeritus professor Don Cox has passed away

Profile photo of Don Cox
Don Cox

Professor Emeritus Donald P. Cox passed away October 26, 2022. He was 79. A plasma astrophysicist, Cox contributed many years to research in his scientific field, to students with whom he worked, and to the department’s teaching mission.

Cox came to the UW–Madison physics department in 1969 with the promise of a faculty position a year before receiving his PhD from the University of California, San Diego. Except for an extended leave of absence at Rice University while his wife completed her degree in Houston, Cox spent his entire professional career here.

He arrived in the era of a cold and quiet interstellar medium and a newly discovered and unexplained soft X-ray background. For the next four years, he and his students did much of the original work on X-ray plasma emissions from supernova remnants, combining a broad physical insight into global processes with laborious and careful compilations of the necessary atomic physics. At this time, astronomers were still searching for the source of the X-ray background, having apparently eliminated all viable production mechanisms.

Cox looked beyond his remnants and realized that the uniform cold medium that he had been producing them in was incompatible with their collective effects on it. He proceeded to turn astronomy’s conventional picture on its head, proposing the hot, violent, and dynamic picture of the interstellar medium that is taught today as a matter of fact. His subsequent work was marked by a lack of respect for convention and a desire to apply basic physics principles to the complexities of interstellar dynamics. His insight that star formation must have a negative feedback effect on future star formation is today a central tenant of research on galactic evolution.

In following his own path, Cox developed an international reputation as the most original thinker in his field. His legacy of fundamentally new ideas is supplemented by two generations of his students who continue his work.

The other side of Cox’s career at Wisconsin was his dedication to teaching, attested to by his many years as leader of the department’s undergraduate program, his election as a fellow of the Teaching Academy, and numerous unsolicited testimonials from students. His interest in teaching was clearly fueled by a desire to share his own joy and fascination with the ideas of physics. He spent hours with pencil and paper, solving a problem that had nothing to do with his research, just to show that some seemingly complex behavior can be derived from basic principles. He did this out of personal curiosity, but his willingness to share his enjoyment of the result was well known.

Modified from Department Archives, with special thanks to Prof. Dan McCammon for contributing to this piece

Please visit the department’s tribute page to Don Cox to submit and/or read stories from Don’s colleagues.

Gary Shiu awarded DOE funding to apply string theory lessons to AI

This post is modified from one originally published by the US Department of Energy

The U.S. Department of Energy (DOE) announced $4.3 million in funding for 16 projects in artificial intelligence (AI) research for high energy physics (HEP), including one from UW–Madison physics professor Gary Shiu for his work on applying knowledge gained from string theory research to improving AI techniques.

profile photo of Gary Shiu
Gary Shiu

These awards support the DOE Office of Science initiative in artificial intelligence research to use AI techniques to deliver scientific discoveries that would not otherwise be possible, and to broaden participation in high energy physics research.

“AI and Machine Learning (ML) techniques in high energy physics are vitally important for advancing the field,” said Gina Rameika, DOE Associate Director of Science for High Energy Physics. “These awards represent new opportunities for university researchers that will enable the next discoveries in high energy physics.”

String theory addresses one of the deepest problems of contemporary physics, namely the reconciliation of gravity and quantum theory. It presents an enormously complex system that is well suited as a testbed for advancing AI techniques. The space of string theory solutions is vast, and the associated energy landscape is high-dimensional, computationally complex, and in general non-convex with unknown hidden structures. In recent years, a variety of AI methods have been used to tackle the string landscape.

“Now, the time is ripe for the pendulum to swing back: through studies of the string landscape, novel optimizers as well as AI techniques for discovering hidden structures of complex multi-dimensional data spaces are emerging,” Shiu says. “We propose to export lessons from string theory to advance AI algorithms generally for computationally complex constrained systems.”

Shiu expects that lessons drawn from this work would then be applied generally to AI applications in other large-scale computational problems.