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.

Host : Prof. Bohm-Jung Yang