Quantum engine efficiency bound beyond the second law of thermodynamics

Area of Science:

• Thermodynamics
• Quantum Mechanics
• Quantum Engineering

Background:

• The Carnot bound, a cornerstone of classical thermodynamics, limits the efficiency of cyclic heat engines operating between two thermal baths.
• Quantum engines, particularly those interacting with squeezed-thermal baths, have demonstrated the potential to surpass the Carnot efficiency limit.
• The reversibility condition, crucial for the Carnot bound, may lead to unachievable efficiency bounds (above unity) for quantum engines with non-thermal baths.

Purpose of the Study:

• To identify the fraction of energy exchange between a quantum system and a bath that intrinsically leads to entropy change.
• To derive a novel inequality governing this entropy change in quantum systems.
• To establish a new, achievable efficiency bound for quantum engines powered by non-thermal baths.

Main Methods:

• Analysis of energy exchange dynamics between quantum systems and baths.
• Derivation of a fundamental inequality for entropy change.
• Application of the derived inequality to establish quantum engine efficiency bounds.

Main Results:

• Identified the specific portion of exchanged energy responsible for entropy increase.
• Formulated a new inequality that constrains entropy changes in quantum systems.
• Established an efficiency bound for quantum engines utilizing non-thermal baths, which does not necessitate reversibility.

Conclusions:

• The derived efficiency bound for quantum engines is applicable even when baths are non-thermal.
• This bound is distinct from classical thermodynamic constraints and does not imply reversibility unless both baths are thermal.
• The findings suggest that understanding quantum engine efficiency requires considerations beyond traditional thermodynamic laws.