Numerically "exact" simulations of a quantum Carnot cycle: Analysis using thermodynamic work diagrams

Area of Science:

• Quantum thermodynamics
• Open quantum systems
• Non-Markovian dynamics

Background:

• Quantum heat engines offer insights into fundamental thermodynamic principles.
• Understanding system-bath interactions is crucial for engine efficiency.
• Previous models often simplified system-bath coupling dynamics.

Purpose of the Study:

• To investigate the efficiency of a quantum Carnot engine under nonperturbative and non-Markovian system-bath coupling.
• To analyze the role of time-dependent external fields in controlling engine processes.
• To compute quantum thermodynamic variables and explore work diagrams.

Main Methods:

• Utilized open quantum dynamics theory.
• Employed hierarchical equations of motion for numerical simulations.
• Applied time-dependent external fields for isothermal, isentropic, and system-bath coupling control.
• Introduced thermodynamic work diagrams for analysis.

Main Results:

• Evaluated work and heat exchange rigorously.
• Identified system-bath interaction fields as significant work sources in strong coupling regimes.
• Demonstrated that maximum efficiency is achieved in the quasi-static case.
• Showcased efficiency being solely dependent on bath temperatures, irrespective of coupling strength.

Conclusions:

• The quantum Carnot engine's efficiency is numerically consistent with Carnot's theorem.
• System-bath coupling strength does not affect the maximum achievable efficiency.
• External fields play a critical role in work extraction and engine performance.