Talk by Professor Arnab Sen, School of Physics, IACS, Kolkata, India at QASTM seminar
Channel: Sayantan Choudhury
Date: 12/07/2021

Title: Quantum Scars and Hilbert space fragmentation in many-body systems

Abstract: The eigenstate thermalization hypothesis (ETH) is believed to be true for generic quantum many-body systems and explains how local equilibration is achieved even with purely unitary dynamics. It is equally interesting to understand how ETH might be violated in interacting systems. Two well-known routes are provided by integrability and many-body localization with strong disorder. Here, I discuss other alternatives for non-integrable disorder-free systems where ETH is violated due to the presence of highly thermal eigenstates embedded in an otherwise ETH-satisfying spectrum. Their direct physical manifestation is to cause anomalous dynamics from some simple initial conditions while most initial states rapidly thermalize. As examples, I will discuss two particular spin models in constrained Hilbert spaces, a PXP model and a U(1) quantum link model, both of which can also be mapped to lattice gauge theories and demonstrate two completely different mechanisms for producing anomalous eigenstates called "quantum many-body scars". If time permits, I will discuss another non-integrable model which possesses a large number of high-energy eigenstates that continue to have a quasiparticle description (typically associated with low-energy states) due to a mechanism called "Hilbert space fragmentation".

Speaker: Professor Arnab Sen, School of Physics, IACS, Kolkata, India.

Date and Time: 12th July 2021, 6.30 PM to 9.00 PM India time (3:00 PM to 5.30 PM Berlin time).

Zoominar link: https://mpi-aei.zoom.us/j/97623339163

Contact: Dr. Sayantan Choudhury (sayantan.choudhury@niser.ac.in)