Séminaire du LPTMS : Sanjay Moudgalya (Caltech)

Thursday, February 09 2023 at 15:00:00

Unconventional Symmetries in Quantum Many-Body Physics

Sanjay Moudgalya (Caltech)

Special day and time: Thursday, 3pM!

Zoom seminar:

https://cnrs.zoom.us/j/98434226211?pwd=dGJHSlgrNDNhbDcyUE1KdzBSQjc1Zz09 Meeting ID: 984 3422 6211 Passcode: RbqTd5

The study of symmetry lies at the heart of various parts of physics. In equilibrium physics, symmetries are useful in classifying phases of matter and in non-equilibrium physics, they are necessary to understand the phenomenon of thermalization. Most symmetries conventionally studied in the literature are examples of so-called on-site unitary symmetries, which have a nice group structure. While such symmetries are sufficient to explain several physical phenomena, recent discoveries of dynamical phenomena known as weak ergodicity breaking have called for a generalization of the notion of symmetry. The conventional theory of thermalization in quantum many-body systems assumes that all subspaces of the Hilbert space that are closed under the dynamics of the system can be understood in terms of the symmetries. However, systems exhibiting weak ergodicity breaking possess additional closed subspaces that cannot be explained in terms of conventional symmetries, which leads to a breakdown of conventional thermalization in such systems. In this talk, I will discuss the physics of weak ergodicity breaking, particularly the phenomena of Hilbert space fragmentation and quantum many-body scars, and how it motivates a general mathematical framework to define symmetries in quantum many-body systems. This framework leads to a generalization of the notion of symmetry beyond the conventional ones, provides precise explanation of weak ergodicity breaking in terms of unconventional symmetries, unifies the study of various different dynamical phenomena in the literature, and also opens up several questions on the nature of symmetry in quantum many-body physics.

References:

https://arxiv.org/abs/2108.10324

https://arxiv.org/abs/2209.03370

https://arxiv.org/abs/2209.03377

Petit amphi, bâtiment Pascal n° 530