Dual-Fermion approach to Non-equilibrium strongly correlated problems

TL;DR

This paper extends the dual fermion approach to non-equilibrium strongly correlated systems, enabling the study of relaxation effects in quantum systems using a dual perturbation theory on the Keldysh contour.

Contribution

It generalizes the dual fermion method to non-equilibrium problems and formulates a dual perturbation theory on the Keldysh contour for time-dependent systems.

Findings

Successfully applied to closed and open quantum systems

Demonstrates relaxation effects from fermionic baths

Provides an efficient impurity solver for non-equilibrium problems

Abstract

We present a generalization of the recently developed dual fermion approach introduced for correlated lattices to non-equilibrium problems. In its local limit, the approach has been used to devise an efficient impurity solver, the superperturbation solver for the Anderson impurity model (AIM). Here we show that the general dual perturbation theory can be formulated on the Keldysh contour. Starting from a reference Hamiltonian system, in which the time-dependent solution is found by exact diagonalization, we make a dual perturbation expansion in order to account for the relaxation effects from the fermionic bath. Simple test results for closed as well as open quantum systems in a fermionic bath are presented.