Derivation of Gravitational Field Equation from Entanglement Entropy

In this paper, I am going to reformulate my previous work on emergent general relativity from quantum information metric (arXiv:1310.1831) so that we can relate it with some other results based on the entropy-energy relation. For this purpose, I propose a new equality that the second derivative of the entanglement entropy directly represents the spacetime metric. Then, we derive the Einstein tensor from the metric, and consider the meaning of emergent energy-momentum tensor. I demonstrate an explicite example based on spatially one-dimensional quantum states near criticality.