Maxwell’s demon with antidecoherence

Subsystems of a composite system in a pure state generally exist in mixed states and undergo changes with the overall state. This phenomenon arises from the coherence of the entire system and represents a crucial distinction between quantum and classical systems. Such a quantum property can enhance the work output of an Otto heat engine composed of two qubits, whose parameters evolve in opposite directions. When the energy levels of the two qubits are identical at one of the thermal equilibrium states of the Otto cycle and there is no interaction between them, the total work output is strictly negative, which is guaranteed by the second law of thermodynamics. However, the interaction-induced coherence allows for positive work output under such conditions. Our model provides an autonomous implementation of Maxwell’s demon, where the measurement and feedback operations are driven by an adiabatically evolved Hamiltonian without external intervention. Furthermore, the coherence of the entire system is amplified by the heat reservoir after measurement, which is the key of the positive work output. Conversely, the quantum measurement-erase cycle typically outputs negative work, attributed to the decoherence of the instrument during the measurement process.