# Performance of continuous quantum thermal devices indirectly connected to environments

## TL;DR

This paper investigates how indirect connections via quantum wires affect the performance of quantum thermal devices, revealing that such couplings introduce irreversible effects that prevent reaching Carnot efficiency.

## Contribution

It introduces a graph-based analysis of quantum thermodynamics networks, identifying circuit mechanisms that influence device performance under indirect coupling.

## Key findings

- Additional decay channels modify heat currents.
- Irreversible contributions prevent reaching Carnot efficiency.
- Performance can be characterized by circuit representatives.

## Abstract

A general quantum thermodynamics network is composed of thermal devices connected to the environments through quantum wires. The coupling between the devices and the wires may introduce additional decay channels which modify the system performance with respect to the directly-coupled device. We analyze this effect in a quantum three-level device connected to a heat bath or to a work source through a two-level wire. The steady state heat currents are decomposed into the contributions of the set of simple circuits in the graph representing the master equation. Each circuit is associated with a mechanism in the device operation and the system performance can be described by a small number of circuit representatives of those mechanisms. Although in the limit of weak coupling between the device and the wire the new irreversible contributions can become small, they prevent the system from reaching the Carnot efficiency.