Quantum quenches from an excited state

Determining the role of initial conditions in late time evolution is a key issue for theory nonequilibrium dynamics isolated quantum systems. Here we extend quenches to case which before quench system an excited state. In particular, show perturbatively size (and arbitrarily strong interactions among quasiparticles) that persistent oscillations one-point functions require presence one-quasiparticle contribution state, as originally shown [J. Phys. A 47 (2014) 402001] from ground Also present case, argue results generically have nonperturbative implications. Oscillations staying undamped within accessible interval, far beyond perturbative scale, are nowadays observed numerical simulations.