# Excitation transport in quantum devices: analytical time-dependent non-equilibrium green function algorithm

## TL;DR

This paper introduces an analytical time-dependent non-equilibrium Green function algorithm to study photon-assisted transport in quantum devices, demonstrating improved stability and insights into charge transfer effects in open quantum systems.

## Contribution

The paper develops a novel analytical TD-NEGF algorithm for quantum transport, enhancing numerical stability and understanding of charge dynamics in open quantum systems.

## Key findings

- Analytical algorithms outperform numerical integrals in stability for large times
- Charge transfer corrections clarify non-physical transport issues
- Long-time current converges to steady-state values

## Abstract

This research demonstrates analytical time-dependent non-equilibrium green function (TD-NEGF) algorithms to investigate dynamical functionalities of quantum devices, especially for photon-assisted transports. Together with the lumped element model, we also study the effects of transiently-transferring charges to reflect the non-conservation of charges in open quantum systems, and implement numerical calculations in hetero-junction systems composed of functional quantum devices and electrode-contacts (to the environment). The results show that (i) the current calculation by the analytical algorithms, versus those by conventional numerical integrals, presents superior numerical stability on a large-time scale, (ii) the correction of charge transfer effects can better clarify non-physical transport issues, e.g. the blocking of AC signaling under the assumption of constant device charges, (iii) the current in the long-time limit validly converges to the steady value obtained by standard time-independent density functional calculations, and (iv) the occurrence of the photon-assisted transport is well-identified.