  An exponential deformation of a 1D critical Hamiltonian, with couplings
falling on a length scale $h^{-1}$, gives rise to ground states whose
entanglement entropy follows a volume law, i.e. the area law is violated
maximally. The ground state is now in the so-called {\em rainbow phase}, where
valence bonds connect sites on the left half with their symmetric counterparts
on the right. Here we discuss some of the most relevant features of this
rainbow phase, focusing on the XX and Heisenberg models. Moreover, we show that
the rainbow state can be understood either as a thermo-field double of a
conformal field theory with a temperature proportional to $h$ or as a massless
Dirac fermion in a curved spacetime with constant negative curvature
proportional to $h$. Finally, we introduce a study of the time-evolution of the
rainbow state after a quench to a homogeneous Hamiltonian.
