Entanglement spectrum of geometric states

Abstract

The reduced density matrix of a given subsystem, denoted by $\rho_A$, contains the information on subregion duality in a holographic theory. We may extract the information by using the spectrum (eigenvalue) of the matrix, called entanglement spectrum in this paper. We evaluate the density of eigenstates, one-point and two-point correlation functions in the microcanonical ensemble state $\rho_{A,m}$ associated with an eigenvalue $\lambda$ for some examples, including a single interval and two intervals in vacuum state of 2D CFTs. We find there exists a microcanonical ensemble state with $\lambda_0$ which can be seen as an approximate state of $\rho_A$. The parameter $\lambda_0$ is obtained in the two examples. For a general geometric state, the approximate microcanonical ensemble state also exists. The parameter $\lambda_0$ is associated with the entanglement entropy of $A$ and R\'enyi entropy in the limit $n\to \infty$. As an application of the above conclusion we reform the equality case of the Araki-Lieb inequality of the entanglement entropies of two intervals in vacuum state of 2D CFTs as conditions of Holevo information. We show the constraints on the eigenstates. Finally, we point out some unsolved problems and their significance on understanding the geometric states.