Quasiparticle picture

Silvia N. Santalla, Giovanni Ramírez, Sudipto Singha Roy +2 more

The time evolution of a quantum state with short-range correlations after a quench to a one-dimensional critical Hamiltonian can be understood using the quasiparticle picture, which states that local entanglement spreads as if it was carried by quasiparticles which separate at a fixed speed. We extend the quasiparticle picture using the recently introduced link representation of entanglement, allowing us to apply it to initial states presenting long-range correlations. The entanglement links are current correlators, and therefore follow a wave equation on the appropriate configurational space which allows us to predict the time evolution of the entanglement entropies. Our results are checked numerically for free fermionic chains with different initial entanglement patterns.

Orlando Luongo

Péter R. Śurján

Xhek Turkeshi, Marcello Dalmonte, Rosario Fazio +1 more

Entanglement is a key tool to classify quantum phases of matter in and out of equilibrium. Here, the authors introduce a phenomenological quasiparticle picture for entanglement dynamics in monitored systems evolving under the effect of quantum jumps. Within this picture, entanglement is carried by non-Hermitian quasiparticles, associated to the no-click limit of the measurement protocol, that propagate ballistically and are randomly reset with a rate given by their inverse lifetime. The authors show how this picture qualitatively reproduces the entanglement transition in the monitored Ising chain.

Klaus Morawetz

Abstract The gradient approximations of the Kadanoff and Baym equations are derived up to first order. The off-shell motions responsible for the satellites are shown to ensure causality. The cancellation of off-shell motions from the drift and correlation part of the reduced density provides a precursor of the kinetic equation for the quasiparticle distribution which leads to a functional between reduced and quasiparticle distribution, named the extended quasiparticle picture. Virial corrections appear as internal gradients in the selfenergy and therefore in the considered processes. With this extended quasiparticle picture, the non-Markovian kinetic equations are transformed into Markovian ones for proper defined quasiparticles without neglect showing the exact cancellation of off-shell parts. Alternative approaches are discussed for comparison.