  In expanding universes, the entanglement entropy must be time-dependent
because the background geometry changes with time. For understanding time
evolution of quantum correlations, we take into account two distinct
holographic models, the dS boundary model and the braneworld model. In this
work, we focus on two-dimensional expanding universes for analytic calculation
and comparison. Although two holographic models realize expanding universes in
totally different ways, we show that they result in the qualitatively same
time-dependence for eternal inflation. We further investigate the
time-dependent correlations in the radiation-dominated era of the braneworld
model. Intriguingly, the holographic result reveals that a thermal system in
the expanding universe is {\it dethermalized} after a critical time
characterized by the subsystem size.
