Multipartite entanglement after a quantum quench

We study the multipartite entanglement of a quantum many-body system undergoing a quantum quench. We quantify the multipartite entanglement through the quantum Fisher information (QFI) density, and we are able to express it after a quench in terms of a generalised response function. For pure state initial conditions and in the thermodynamic limit, we can express the QFI as the fluctuations of an observable computed in the so-called diagonal ensemble. We apply the formalism to the dynamics of a quantum Ising chain, after a quench in the transverse field. In this model the asymptotic state is, in almost all cases, more than two-partite entangled. Moreover, starting from the ferromagnetic phase, we find a divergence of multipartite entanglement for small quenches closely connected to a corresponding divergence of the correlation length.