Unlocking thermodynamic multitasking: Exploring the functioning of two-qubit engines through coherence and entanglement

TL;DR

This paper investigates how quantum coherence and entanglement influence the operation and efficiency of two-qubit quantum heat engines and refrigerators, considering both local and global dissipation effects and the role of external coherence.

Contribution

It introduces a comprehensive analysis of two-qubit engines with two heat baths, exploring the impact of coherence, entanglement, and dissipation on operational modes and efficiency.

Findings

Optimal parameters for maximum engine and refrigerator performance identified.

Quantum coherence outside the system affects thermodynamic quantities.

Entanglement and coherence play observable roles in operational regime transitions.

Abstract

Recent studies have investigated the role of entanglement in the operation of a two-qubit system as a heat engine, showing that work can be extracted from a single heat bath without direct heat dissipation between the two-qubit system and the cold bath (2021 Phys. Rev. Lett, 126, 120605). In this work, we explore the impact of operating the same two-qubit system model with two heat baths and direct dissipation to the environment by applying both a local and a global Markovian master equation. The addition of a second heat bath enables the system to operate in different modes depending on the initial quantum state. We examine the temporal behavior of concurrence entanglement and quantum coherence, analyzing their observable roles in transitions between various operational regimes. Additionally, we investigate the evolution of information flow throughout the working cycle of the two-qubit system, focusing on the influence of individual and collective decoherence on the system's efficiency and operational modes. We identify the optimal parameter regions for the engine and refrigerator modes to achieve maximum performance. Finally, we investigate the effect of coherence outside the system on its thermodynamic quantities.