Simulating the out-of-equilibrium dynamics of local observables by trading entanglement for mixture

Abstract

The fact that the computational cost of simulating a many-body quantum system on a computer increases with the amount of entanglement has been considered as the major bottleneck for simulating its out-of-equilibrium dynamics. Some aspects of the dynamics are, nevertheless, robust under appropriately devised approximations. Here we present a possible algorithm that allows to systematically approximate the equilibration value of local operators after a quantum quench. At the core of our proposal there is the idea to transform entanglement between distant parts of the system into mixture, and at the same time preserving those conserved quantities that can be expressed as a sum of local densities. We benchmark the resulting algorithm by studying quenches of quadratic Fermionic Hamiltonians.