Entanglement Entropy and its Quench Dynamics for Pure States of the Sachdev-Ye-Kitaev model

Sachdev-Ye-Kitaev (SYK) is a concrete solvable model with non-Fermi liquid behavior and maximal chaos. In this work, we study the entanglement R\'enyi entropy for the subsystems of the SYK model in the Kourkoulou-Maldacena states. We use the path-integral approach and take the saddle point approximation in the large-$N$ limit. We find a first-order transition exist when tuning the subsystem size for the $q=4$ case, while it is absent for the $q=2$ case. We further study the entanglement dynamics for such states under the real-time evolution for noninteracting, weakly interacting and strongly interacting SYK(-like) models.