Performance limits of multilevel and multipartite quantum heat machines

Area of Science:

• Quantum thermodynamics
• Quantum heat engines
• Quantum information science

Background:

• Quantum heat machines utilize quantum systems as working media.
• Coherence in quantum systems can influence thermodynamic processes.
• Understanding the role of quantum properties is crucial for optimizing heat engine performance.

Purpose of the Study:

• To investigate the role of coherence in quantum heat machines.
• To determine if coherence is a thermodynamic asset for heat engines.
• To explore the impact of level degeneracy on machine performance.

Main Methods:

• Developed a general theory for a quantum heat machine using an N-level system.
• Analyzed both reciprocating and continuous cycles coupled to heat baths.
• Investigated the influence of transition-dipole vector orientations and level degeneracy.

Main Results:

• Machine performance depends on transition-dipole vector orientations.
• Aligned dipoles lead to coherence but also dark states, hindering performance.
• Level degeneracy enhances heat currents and power output, irrespective of coherence.

Conclusions:

• Level degeneracy, not coherence, is a key thermodynamic resource.
• Degeneracy improves heat currents and power output of quantum heat machines.
• Quantum heat machine efficiency is limited by the Carnot bound, unaffected by degeneracy.