Entanglement evolution across a conformal interface

Abstract: For two dimensional conformal field theories in the ground state, it is known that a conformal interface along the entanglement cut can suppress the entanglement entropy from $S_A\sim c\log L$ to $S_A\sim c_{\text{eff}}\log L$, where $L$ is the length of the subsystem $A$, and $c_{\text{eff}}\in [0, c]$ is the effective central charge which depends on the transmission property of the conformal interface. In this work, by making use of conformal mappings, we show that a conformal interface has the same effect on entanglement evolution in non-equilibrium cases, including global, local and certain inhomogeneous quantum quenches. I.e., a conformal interface suppresses the time evolution of entanglement entropy by effectively replacing the central charge $c$ with $c_{\text{eff}}$, where $c_{\text{eff}}$ is exactly the same as that in the ground state case. We confirm this conclusion by a numerical study on a critical fermion chain. Furthermore, based on the quasi-particle picture, we conjecture that this conclusion holds for an arbitrary quantum quench in CFTs, as long as the initial state can be described by a regularized conformal boundary state.