1. frustration-induced athermal behaviors: hilbert space fragmentation and quantum many-body scars

Kyungmin Lee

National High Magnetic Field Laboratory

26 May 2021 Wed 11.30 am

                                      IBS Center for Theoretical Physics of Complex Systems (PCS), Administrative Office (B349), Theory Wing, 3rd floor

                                      Expo-ro 55, Yuseong-gu, Daejeon, South Korea, 34126 Tel: +82-42-878-8633                     

Although most interacting quantum systems thermalize locally on short time scales independent of initial conditions, recent developments have shown that this is not always the case: Athermal behaviors have been observed in disordered systems, and more recently, evidence for athermal eigenstates, known as quantum many-body scars, has emerged in disorder-free models with constrained dynamics. In this talk, I will demonstrate that geometric frustration provides a pathway to athermal behaviors without disorder. In a clean system, local constraints can lead to a fragmented Hilbert space where certain initial states fail to reach the thermal steady state. Such fragmentation naturally arises in many frustrated systems with low-energy “ice manifolds” which gives rise to a broad range of relaxation times for different initial states. Focusing on the highly frustrated kagome lattice, I will discuss the phenomenology of fragmentation in two spin-1/2 Hamiltonians with simple two-body interactions: the Balents-Fisher-Girvin model (easy-axis regime), and the three-coloring model (easy-plane regime), both with constrained Hilbert spaces. Furthermore, I will discuss the existence of quantum many-body scar eigenstates in modified three-coloring models with robust quantum revivals, which can be generalized to other lattices.