Quenched coupling, entangled equilibria, and correlated composite operators: a tale of two O(N) models

Authors: Souvik Banerjee, Julius Engelsöy, Jorge Larana-Aragon, Bo Sundborg, Larus Thorlacius, Nico Wintergerst.

Preprint number: UUITP-10/19

A macroscopic version of Einstein-Podolsky-Rosen entanglement is obtained by quenching a linear coupling between two O(N) vector models. A quench of the mixed vacuum produces an excited entangled state, reminiscent of puried 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. Approximately thermal behaviour is obtained in the limit of weak initial mixing and 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.