  A macroscopic version of Einstein-Podolsky-Rosen entanglement is obtained by
quenching a quadratic coupling between two O(N) vector models. A quench of the
mixed vacuum produces an excited entangled state, reminiscent of purified
thermal equilibrium, whose properties can be studied analytically in the free
limit of the individual field theories. The decoupling of different wavelength
modes in free field theory prevents true thermalisation but a more subtle
difference is that the density operator obtained by a partial trace does not
commute with the post-quench Hamiltonian. Generalized thermal behaviour is
obtained at late times, in the limit of weak initial mixing or a smooth but
rapid quench. More surprisingly, late-time correlation functions of composite
operators in the post-quench free field theory share interesting properties
with correlators in strongly coupled systems. We propose a holographic
interpretation of our result.
