Sorin T. Popa

Biosketch

I was born in 1953 in Bucharest, Romania. I studied at the University of Bucharest, getting a BS in 1976, an MS in 1977, with Ciprian Foias as mentor, and a PhD in 1983, with Dan Voiculescu as adviser. From 1978 to 1987 I was a researcher at the Institute of Mathematics in Bucharest. In 1987 I emigrated with my wife and son to the US, being a professor of mathematics at UCLA ever since then. I was the Chair of the UCLA math department from 2009 to 2012. I am holding the Takesaki Endowed Chair at UCLA since 2018. I spent the year 1991-1992
as a member of the Institut des Hautes Etudes Scientifiques in Paris and the year 1997-1998 as a Professor at the Universite de Geneve. In 2009 I was the recipient of the Chaire Blaise Pascal at College de France in Paris. In 2016-2017 I held the Chaire Hadamard of the FSMS at the Univerisite de Paris, Orsay. I was an invited speaker at ICM 1990 in Kyoto and a plenary speaker at ICM 2006 in Madrid. I received a Guggenheim Fellowship in 1995, the Ostrowski Prize in 2009 and the E.H. Moore Prize of the American Mathematical Society in 2010. In 2013 I was elected Fellow the American Academy of Arts and Sciences and Fellow of the American Mathematical Society. In 2025 I was elected member of the National Academy of Sciences.

Research Interests

I am an analyst working in C*-algebras and W*-algebras, subfactors and quantum symmetries, ergodic theory and the dynamics of groups acting on spaces, with a main interest on rigidity aspects pertaining to these areas.
My work during the 1990s provided foundational tools in subfactor theory, such as a probabilistic and entropic
definitions of the Jones index, the discovery of the notion of amenability for subfactors and their graphs, and for quantum symmetries, with the complete classification of such objects in terms of their standard invariant, reconstruction methods, a quantum double construction, a representation theory and an L2-cohomology theory for subfactors and quantum symmetries. During 2001-2006 I have developed a powerful new method for
studying II1 factors, now called deformation-rigidity theory. It is based on my discovery that if the geometric data G underlying a II1 factor contains sufficient ``soft '' and ``rigid'' informations, then G can be recovered from the isomorphism class of its II1 factor L(G), through a series of random-versus-structure techniques that I have introduced. This led to many striking applications, by many people, including W*-superrigidity results for Bernoulli actions of non-amenable product groups, with the complete classification of the associated II1 factors and calculation of their symmetry groups. This has become over the last 20 years a very dynamic area of research, with a constant flow of new ideas and results.