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Correlated quantum machines beyond the standard second law
1Institute for Theoretical Physics I, University of Stuttgart, D-70550 Stuttgart, Germany.
Science Advances
|October 10, 2025
Summary
We derived a new formula for quantum engine efficiency, accounting for system-environment correlations. This reveals an athermal regime where efficiency exceeds standard limits by using entropic resources.
Area of Science:
- Quantum Thermodynamics
- Statistical Mechanics
- Quantum Information
Background:
- Standard thermodynamics applies to macroscopic, uncorrelated systems.
- Microscopic quantum systems exhibit correlations with their environment, violating standard thermodynamic laws.
- Existing models often neglect these crucial quantum correlations.
Purpose of the Study:
- To derive an exact efficiency formula for cyclically driven quantum engines.
- To develop generalized laws of quantum thermodynamics that include all correlations.
- To explore novel operating regimes beyond classical thermodynamic limits.
Main Methods:
- Utilized generalized laws of quantum thermodynamics.
- Developed a formalism to account for all initial and system-environment correlations.
- Analyzed cyclically driven quantum engines.
Main Results:
- Derived an exact formula for quantum engine efficiency, incorporating all correlations.
- Identified two operational modes: a standard thermal regime and a novel athermal regime.
- Demonstrated that efficiency in the athermal regime is not limited by the Carnot bound.
Conclusions:
- The new formalism unifies the study of quantum engine efficiency.
- Correlations, particularly entropic resources like system-bath correlations, unlock new thermodynamic possibilities.
- Quantum thermodynamics offers a richer framework for understanding and designing microscopic heat engines.
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