Classical emulation of quantum-coherent thermal machines

Area of Science:

• Quantum Thermodynamics
• Quantum Information Science
• Statistical Mechanics

Background:

• Continuous quantum thermal machines often exhibit performance enhancements attributed to quantum coherences.
• The concept of 'quantum-thermodynamic supremacy' suggests these coherences are essential for superior performance.
• Investigating the necessity of quantum coherences in quantum thermal machine operation is crucial.

Purpose of the Study:

• To determine if quantum coherences are always essential for performance enhancements in quantum thermal machines.
• To compare the performance of a three-level quantum refrigerator with a four-level combined cycle model.
• To explore the possibility of classical emulation for coherent quantum thermal machines.

Main Methods:

• Comparative analysis of a power-driven three-level quantum refrigerator and a four-level combined cycle refrigerator in the weak driving regime.
• Focus on quantifying cooling rate and coefficient of performance.
• Development of a classical representation using graph theory to model thermodynamic variables.

Main Results:

• The four-level model demonstrates superior performance, operating in regimes inaccessible to the three-level model, with higher cooling rates and better coefficients of performance.
• The observed improvement in cooling rate directly correlates with the increase in stationary quantum coherences.
• Thermodynamic variables for both models can be derived from a classical graph-theory-based representation.

Conclusions:

• Quantum coherences are not always essential for achieving enhanced performance in quantum thermal machines.
• Coherent quantum refrigerators can be emulated by incoherent stochastic-thermodynamic models, implying classical replicability.
• For N-level weakly driven devices with cyclic transitions, quantum effects may not be fundamentally required for the observed energy conversion processes.