Illinois Physics celebrates the new Anthony J. Leggett Institute for Condensed Matter Theory

Faculty and friends recently celebrated Illinois Physics Professor Tony Leggett with the renaming of the Institute for Condensed Matter Theory and a new post-doctoral fellowship—just after the 20th anniversary of Leggett’s Nobel Prize.

By Bill Bell for Illinois Physics

Alongside Shakespeare’s sonnets

Tony Leggett arrived as a postdoctoral researcher at the University of Illinois Urbana-Champaign with “nothing more than an unpublished, one-page Physics Letter”' and a PhD from Oxford. “My credentials, such as they were. How times have changed!” he said recently.

Times have changed, indeed. An unparalleled career has followed, including Dirac and Maxwell Medals from the Institute of Physics, a MacArthur Chair, a Nobel Prize for his work in low-temperature physics and superfluidity, and a Knighthood of the Order of the British Empire.

In November 2023, colleagues met to honor Leggett and to rename the University of Illinois institute where he serves as chief scientist. It is now the Anthony J. Leggett Institute for Condensed Matter Theory (AJL-ICMT). The institute’s 16 faculty members advise more than 70 graduate students per year on a breadth of topics in condensed matter research.

The praise for Leggett was poetic, well-deserved, and appropriate for a physicist who began his time at Oxford as a student of classics, philosophy, and ancient history.

“Your beautiful work advances science and lifts the human spirit. I put it alongside Shakespeare's sonnets as a gift to humanity."

Professor Paul Goldbart, former director of the AJL-ICMT

“Your beautiful work advances science and lifts the human spirit. I put it alongside Shakespeare’s sonnets as a gift to humanity,” Professor Paul Goldbart said at the event. 

Goldbart was AJL-ICMT’s first director in the 2000s and went on to serve as provost at Stony Brook University. He was also the first at Leggett’s door on October 7, 2003, to congratulate his neighbor on his Nobel Prize—arriving with his two children in tow at 6 a.m., ahead of “the minders and TV trucks.”

Goldbart considers Leggett "an exemplary role model" who conducts himself "with grace and integrity." He told Leggett, "I have been gone from Illinois for years now, so when I talk to colleagues the years have washed away any concerns they might have about my sensitivities. They talk freely. And they say lovely things. Your expertise and tone is known and loved around the world.”

A very reasonable suggestion

Leggett first did a stint at the University of Illinois as a postdoctoral researcher in 1964 and 1965. He returned to the university in 1983 as a professor. 

“After I arrived [in 1964], I didn’t really know what I was supposed to be doing,” Leggett explained. 

“John Bardeen [twice a Nobel winner himself] and Leo Kadanoff [another leader in the study of superconductivity] came into my office and said, ‘Look, John Wheatley down in the basement’—a very famous experimentalist in low-temperature physics—‘is doing these experiments on Helium-3 with a view to determining whether or not it is going to become superfluid, as some theorists have predicted.’ He was able to go down to temperatures as low, if not lower, than anyone else in the world. ‘We suggest you’—that is, me—‘try and work out what you would expect to happen to this spin diffusion coefficient [representing the exchange of spin orientation energy between two neighboring nuclear spins], if the superfluid transition does indeed take place.’ That seemed a very reasonable suggestion, so I started working on it.” 

Helium-3 is an isotope of the element that makes a kid’s party balloon float, and physicists were realizing that, at certain very-low temperatures, it had other interesting properties, as well. Namely, two of the key theories of the day—the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity and Lev Davidovich Landau's Fermi-liquid theory—predicted different behaviors. 

“No one had put [the two theories] together. As it turned out, it was very exciting. There were quantities, because of the Landau Fermi-liquids’ effects, that have a different temperature dependence than had been predicted in BCS theory. Not qualitatively different, necessarily, but certainly quantitatively. It could be seen experimentally,” Leggett said.

“I wrote, first, a short letter, and then a couple of longer papers on it. I gave my first international conference talk. This received a certain amount of attention that I found quite exciting. Had it not been for that, I’m not sure I would have stayed in physics, or at least in university physics. I might have become a high school teacher or something like that. It kept me in the game.”

The Helium-3 game would be at the heart of his work in the coming years. His elucidation of its unprecedented magnetic resonance behavior below 3/1000 of a degree in the 1960s and ‘70s earned him the Nobel Prize in 2003. He shared the prize with Alexei Abrikosov and Vitaly L. Ginzburg.

Cross-cutting and cutting edge

During November’s renaming ceremony, Executive Vice Provost for Academic Affairs Bill Bernhard announced the creation of a new post-doctoral fellowship supported by the campus and The Grainger College of Engineering. The fellowship is named in Leggett’s honor and reflects what Bernhard called a “powerful legacy of collaboration and innovation that continues to improve the lives of countless individuals.”

As he left the University of Illinois at the end of his post-doc year, Tony Leggett swore “an oath to myself…that I would never come back and live permanently in Champaign-Urbana.” Find out what motivated him to make that promise and then break it “rather spectacularly” 20 years later in his autobiography.

That legacy is vast, and it is ongoing, according to Grainger Engineering Dean Rashid Bashir. 

Leggett currently studies topological quantum computing. 

“Tony shaped our understanding of superfluids and what they can do. And now, in a new moment of his career, his work in quantum technology remains cross-cutting and cutting edge.” Bashir also said Leggett exemplifies the Department of Physics’ well-known reputation for “open-door informality that rapidly advances work in the biggest topics of the day.”

That “Urbana Style,” as many call it, was an important part of Leggett’s decision to come to the University of Illinois more than 40 years ago. And it remains a crucial part of his efforts and success.

“The rumors about this place’s ethos, nature, and atmosphere were well-verified when I arrived,” Leggett said. “The collegiality and willingness to take reasonable risks have given me a marvelous sequence of students and collaborators.”

How did you come to the University of Illinois? Why did you think it was exciting? 

The offer from UIUC [in the early 1980s] came pretty much out of the blue. I had been here as a postdoc, 1964-65. I knew John Bardeen, David Pines, Gordon Baym, a whole lot of the people I would be working with and that made it, in fact, extremely attractive.

At first, I thought the chances of my acceptance were very low indeed, but they said “Well, if you think it’s even a five percent chance, then come across and give us a visit and see what you think.” Then when I got back home, I had to really think. I realized that the mere process of considering leaving Sussex had, in some sense, disoriented me, to the extent that, at some point in the next 10 years, I was going to want to leave. And then I thought to myself, it’s very unlikely that I’m going to get as good an offer as one from UIUC.

Let’s jump to the current era of your career. What are you working on these days that’s exciting?

Some of the things I’m trying to think about are topological quantum computing—a very important intellectual development of the last 20 years or so. The nice thing about it is you can’t really do it from particle physics or cosmology. You have to know your condensed matter physics. 

I’m afraid my contributions to [quantum computing] have been rather negative, in that I’ve really tended to cast doubt on if some of the ideas that people had been playing around with are going to work. But it keeps me entertained.

It requires condensed matter physics, you say. Draw that connection a bit more tightly for us.

One of the fundamental problems in quantum computing in general is that its success requires you to keep very careful track of the relative phases of different quantum mechanical states. The moment those phases get screwed up, you're lost. It won’t work. Unfortunately, nature keeps on trying to screw those phases up through decoherence.

About 20 years ago, various people introduced the idea that if you could bury your information deep enough in the complicated states of a many-bodied system, then you might be able to insulate against decoherence. My own skepticism has been with respect to one particular class of systems that people have speculated might work here, so called topological superconductors. It turns out, in fact, that topological superconductors have a great deal in common with superfluidity, which I’ve done a lot of work on.

You used the word skepticism and the idea of casting doubt. Is that an approach you take intentionally or is that buried deep in your personality somewhere?

I think if you asked some of my colleagues, it is a character defect.

Let’s not call it a defect!

A characteristic, then. In my autobiography, I speculated that it might be a consequence of my upbringing. I was brought up as a Catholic in a country where Catholics are in a small minority—in the UK in the ‘40s, ‘50s. From a rather early stage, I had the experience of trying to defend ideas that would not be necessarily consensus among many of my countrymen. I suspect that might have carried over.