Out of equilibrium mean field dynamics in the transverse field Ising model

Abstract: We investigate the quench dynamics of the transverse field Ising model on a finite fully connected lattice as a prime example of non-equilibrium mean field dynamics. Using a rate function approach we compute the leading order corrections to the mean field behavior analytically. Our focus is threefold: i) We analyze the validity of the mean field approximation and observe that deviations can occur quickly even for large systems. ii) We study the variance of the order parameter and identify four qualitative different regions that cannot be distinguished by solely looking at its mean. iii) We derive the complete entanglement Hamiltonian for a bipartition of the lattice, which remarkably turns out to be a time-dependent harmonic oscillator within the validity of the mean field analysis.