Quench action approach for releasing the Néel state into the spin-1/2 XXZ chain

Abstract

The steady state after a quantum quench from the N\\'eel state to the\nanisotropic Heisenberg model for spin chains is investigated. Two methods that\naim to describe the postquench non-thermal equilibrium, the generalized Gibbs\nensemble and the quench action approach, are discussed and contrasted. Using\nthe recent implementation of the quench action approach for this N\\'eel-to-XXZ\nquench, we obtain an exact description of the steady state in terms of Bethe\nroot densities, for which we give explicit analytical expressions.\n Furthermore, by developing a systematic small-quench expansion around the\nantiferromagnetic Ising limit, we analytically investigate the differences\nbetween the predictions of the two methods in terms of densities and postquench\nequilibrium expectation values of local physical observables. Finally, we\ndiscuss the details of the quench action solution for the quench to the\nisotropic Heisenberg spin chain. For this case we validate the underlying\nassumptions of the quench action approach by studying the large-system-size\nbehavior of the overlaps between Bethe states and the N\\'eel state.\n