The Generalized Kadanoff-Baym Ansatz with Initial Correlations

TL;DR

This paper extends the NEGF--GKBA method to incorporate initial correlations, enabling more efficient and accurate simulations of quantum systems out of equilibrium without costly adiabatic procedures.

Contribution

The authors develop a new scheme allowing NEGF--GKBA to handle correlated initial states, improving efficiency and expanding applicability.

Findings

Accurately models initial correlations in NEGF--GKBA

Demonstrates improved computational performance

Validates method with a laser-driven quantum system

Abstract

Within the non-equilibrium Green's function (NEGF) formalism, the Generalized Kadanoff-Baym Ansatz (GKBA) has stood out as a computationally cheap method to investigate the dynamics of interacting quantum systems driven out of equilibrium. Current implementations of the NEGF--GKBA, however, suffer from a drawback: real-time simulations require {\em noncorrelated} states as initial states. Consequently, initial correlations must be built up through an adiabatic switching of the interaction before turning on any external field, a procedure that can be numerically highly expensive. In this work, we extend the NEGF--GKBA to allow for {\em correlated} states as initial states. Our scheme makes it possible to efficiently separate the calculation of the initial state from the real-time simulation, thus paving the way for enlarging the class of systems and external drivings accessible by the already successful NEGF--GKBA. We demonstrate the accuracy of the method and its improved performance in a model donor-acceptor dyad driven out of equilibrium by an external laser pulse.