Efficiency gain and bidirectional operation of quantum engines with decoupled internal levels

Abstract

We present a mechanism for efficiency increase in quantum heat engines containing internal energy levels that do not couple to the external work sink. The gain is achieved by using these levels to channel heat in a direction opposite to the one dictated by the second law. No quantum coherence, quantum correlations or ergotropy are required. A similar mechanism allows the engine to run in reverse and still produce useful work. We illustrate these ideas using a simple quantum Otto cycle in a coupled-spin system. We find this engine also exhibits other counterintuitive phenomenology. For example, its efficiency may increase as the temperature difference between the heat baths decreases. Conversely, it may cease to operate if the hotter bath becomes too hot or the colder bath too cold.

published version with small proof corrections

References in corpus (4)

• Quantum Thermodynamic Cycles and quantum heat engines
• The second law, Maxwell's daemon and work derivable from quantum heat engines
• Quantum correlated heat engine with nonlinear spin-spin interactions
• Entangled quantum heat engines based on two two-spin systems with Dzyaloshinski-Moriya anisotropic antisymmetric interaction

Cited by in corpus (7)

• Measurement-based quantum heat engine in a multilevel system
• Interaction enhanced quantum heat engine
• Enhancing the performance of coupled quantum Otto thermal machines without entanglement and quantum correlations
• Quantum heat engines with complex working media, complete Otto cycles and heuristics
• Spins-based Quantum Otto Engines and Majorisation
• Origin of quantum shape effect
• Algebraic approach to a two-qubit quantum thermal machine