Entanglement of Coarse Grained Quantum Field in the Expanding Universe

Understand

We investigate the entanglement of a quantum field in the expanding universe.

• By introducing a bipartite system using a coarse-grained scalar field, we apply the separability criterion based on the partial transpose operation and numerically calculate the bipartite entanglement between separate spatial regions.
• We find that the initial entangled state becomes separable or dis-entangled after the spatial separation of two points exceed the Hubble horizon.
• This provides the necessary condition for the appearance of classicality of the quantum fluctuation.