Exact finite-time correlation functions for multi-terminal setups: Connecting theoretical frameworks for quantum transport and thermodynamics

TL;DR

This paper derives exact finite-time correlation functions for quantum transport in multi-terminal setups, unifying different theoretical frameworks and clarifying their regimes of validity using a quantum dot model.

Contribution

It provides a unified analytical approach connecting quantum master equations, scattering matrix, and Heisenberg methods for open quantum systems.

Findings

Exact expressions for particle and energy currents and fluctuations

Alignment of Heisenberg, scattering matrix, and master equation results within their regimes

A protocol bridging weak and arbitrary coupling regimes

Abstract

Transport in open quantum systems can be explored through various theoretical frameworks, including the quantum master equation, scattering matrix, and Heisenberg equation of motion. The choice of framework depends on factors such as the presence of interactions, the coupling strength between the system and environment, and whether the focus is on steady-state or transient regimes. Existing literature treats these frameworks independently, lacking a unified perspective. Our work addresses this gap by clarifying the role and status of these approaches using a minimal single-level quantum dot model in a two-terminal setup under voltage and temperature biases. We derive analytical expressions for particle and energy currents and their fluctuations in both steady-state and transient regimes. Exact results from the Heisenberg equation are shown to align with scattering matrix and master equation approaches within their respective validity regimes. Crucially, we establish a protocol for the weak-coupling limit, bridging the applicability of master equations at weak-coupling with Heisenberg or scattering matrix approaches at arbitrary coupling strength.