A scalable numerical approach to the solution of the Dyson equation for the non-equilibrium single-particle Green's function

TL;DR

This paper introduces a scalable numerical method for solving Dyson equations in non-equilibrium Green's function theory, enabling efficient simulations of quantum many-body systems out of equilibrium.

Contribution

The authors develop a self-consistent numerical approach that improves the efficiency of solving Dyson equations by optimizing matrix distribution and communication in parallel computations.

Findings

Effective for quenches in ultracold gases

Reduces communication time in parallel processing

Demonstrates convergence in non-equilibrium scenarios

Abstract

In this work we present a numerical method to solve the set of Dyson-like equations arising the context of non-equilibrium Green's functions. The technique is based on the self-consistent solution of the Dyson equations for the interacting single-particle Green's function once a choice for the self-energy, functional of the single-particle Green's function itself, is done. We briefly review the theory of the non-equilibrium Green's functions in order to highlight the main point useful in discussing the proposed technique. We also discuss the relation between our approach and the textbook approach to solve the Kadanoff-Baym equations. We then present and discuss the numerical implementation which is based on the distribution of the elements of the Green's function and self-energies on a grid of processes. We discuss how the structure of the considered self-energy approximations influences the distribution of the matrices in order to minimize the communication time among processes and which should be considered in the case of other approximations. We give an example of the application of our technique to the case of quenches in ultracold gases, also discussing to the convergence features of our scheme.