Nobelist Tony Leggett: In Memoriam

Tony Leggett

This post commemorates Sir Anthony 'Tony' Leggett, who was awarded the Nobel prize in physics in 2003 (along with V. L. Ginzburg and A. A. Abrikosov), for making pioneering advances in our understanding of physics at low temperatures, and who passed away recently (1938-2026).

Leggett's major contributions included explaining the superfluidity of Helium 3 (an outstanding problem in physics), and pioneering the study of macroscopic phenomena (he was among the first to suggest that quantum mechanics is not confined to the microworld and largely responsible for the 2025 physics Nobel prize; one of the awardees John Clarke said in his Nobel lecture that the work they did was basically trying to answer questions posed by Leggett).

One mark of a great physicist in my opinion is that they leave their name on their discoveries: some examples relevant to the present case - the Leggett-Garg inequality; the Caldeira-Leggett model; the Leggett bound on superfluid fraction. Leggett also wrote a classic text: A.J. Leggett. Quantum Liquids: Bose condensation and Cooper pairing in condensed matter systems (Oxford University Press, 2006). I have used this book extensively in my work.

Commemorative session

I am writing this post in response to a special session held in memory of Tony Leggett at the Atomtronics workshop in Benasque, Spain, which I am currently attending. This workshop is held every two years and in 2024 (which I also attended) Tony was scheduled to give a talk in person, but in the end delivered it via Zoom.

The session was introduced by one of the workshop organizers, Prof. Luigi Amico, who recounted the basic facts of Tony's life. These are also available online: his teacher parents; his birth in London; his first degree (in the classics) and his second degree (in physics), both from Oxford; his professorial positions at Sussex (for 15 years) and Urbana-Champaign (36 years until his retirement in 2019). Luigi also recounted his interactions with Tony, showing photos from the Leggett home in America.

Prof. Sungkit Yip was the next speaker. He had been a graduate student of Tony, and described what it was like to have him as an advisor (got to meet him once a week for an hour, during which the phone was always ringing in Tony's office and someone was waiting outside to meet him; Tony never taught specific techniques to his students, he gave them well-identified problems to flesh out; he insisted on theories being experimentally testable). Yip said collaborators had to learn to decipher Tony's handwriting and showed some of his handwritten notes. I could hardly make out any of the prose, but the equations were clearly legible.

The other speakers were Profs. Rosario Fazio (from Italy) and Prof. Kwek Leong Chuan (from Singapore). An interesting document that was mentioned was Tony's "Notes on the writing of Scientific English for Japanese physicists" with roots likely traceable to his degree in the classics. Kwek, as he is popularly known, had a funny story. Bin Yi, one of Tony's students, recorded an interview with him (available on YouTube). Kwek showed a clip of it. As part of his interview, Yi had brought a present for Tony from China, and was explaining that it blessed the receiver with great qualities like longevity. "Longevity I already have," replied Tony, already in his 80's, his hair totally white.

Summary

The conclusion of the session (many in the audience knew him personally and there was no one who had not read a paper or a book by Leggett) was that Tony was an outstanding scientist whose interest in the deepest questions of physics was motivated by his early training as a philosopher; a great mentor of students and postdocs; and a theoretical physicist who was very close to experiment. Clearly he leaves a great legacy behind.