Island for Gravitationally Prepared State and Pseudo Entanglement Wedge

Abstract

We consider spacetime initiated by a finite-sized boundary on which a pure initial matter state is set as a natural generalization of the Hartle-Hawking noboundary state. We study entanglement entropy of the gravitationally prepared matter state at the final time slice. We find that the entropy of the initial state or the entanglement island gives the entropy for large subregions on the final time slice. Consequently, we find the entanglement entropy is bounded from above by the boundary area of the island, leading to an entropy bound in terms of the island formula. The island I appears in the analytically continued spacetime, either at the bra or the ket part of the spacetime in Schwinger-Keldysh formalism, and the entropy is given by an average of pseudo entropy of each entanglement island. We find a necessary condition of the initial state to be consistent with the strong subadditivity. The condition requires that any probe degrees of freedom are thermally entangled with the rest of the system. We then study which initial condition leads to our finite-sized initial boundary or the Hartle-Hawking no-boundary state. Due to the absence of a moment of time reflection symmetry, the island in our setup requires a generalization of the entanglement wedge, which we call pseudo entanglement wedge. In pseudo entanglement wedge reconstruction, we consider reconstructing the bulk matter transition matrix on A ∪ I, from a fine-grained state on A. The bulk transition matrix is given by a thermofield double state with a projection by the initial state. We provide an AdS/BCFT model, which provides a double holography model of our setup by considering EOW branes with corners. We also find the exponential hardness of such reconstruction task using a generalization of Python's lunch conjecture to pseudo generalized entropy.

Timelike entanglement entropy

“…Remarkably, in Euclidean time-dependent asymptotically AdS spaces, the pseudo entropy is related to the minimal surface area in the same formula as (1.3). See [18][19][20][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] for further related developments. Indeed, in both the timelike EE and the EE in dS/CFT, the reduced density matrices are not Hermitian and thus are not standard von Neumann entropies, but rather pseudo entropies instead.…”