  We use entanglement witnesses related to the entanglement negativity of the
state to detect entanglement in the $XY$ chain in the postquench states in the
thermodynamic limit after a quench when the parameters of the Hamiltonian are
changed suddenly. The entanglement negativity is related to correlations, which
in the postquench stationary state are described by a generalized Gibbs
ensemble, in the ideal case. If, however, integrability breaking perturbations
are present, the system is expected to thermalize. Here we compare the
nearest-neighbor entanglement in the two circumstances.
