![]() ![]() The recent, rapid development of quantum thermodynamics has taken a similar trajectory, and, e.g., “quantum engines” have become a widely studied concept in theoretical research. However, over the centuries, the description of engines, refrigerators, thermal accelerators, and heaters has become so abstract that a direct application of the universal statements to real-life devices is everything but straight forward. Thermodynamics originated in the need to understand novel technologies developed by the Industrial Revolution. Further, the study of complete Otto cycles inherent in the average cycle also yields interesting insights into the average performance. These conditions lead us to a connection between performance of quantum heat engines and the notion of majorization. Analyzing extreme-case scenarios, we formulate heuristics to infer the necessary conditions for an engine with uncoupled as well as coupled spins model. However, the necessary conditions governing engine performance and the relevant upper bound for efficiency are unknown for the general case of arbitrary spin magnitudes. It has been earlier shown that the said interaction provides an enhancement of cycle efficiency for two spin-1/2 particles, with an upper bound which is tighter than the Carnot efficiency. In this paper, we examine the performance of a quasi-static quantum Otto engine based on two spins of arbitrary magnitudes subject to an external magnetic field and coupled via an isotropic Heisenberg exchange interaction. Quantum thermal machines make use of non-classical thermodynamic resources, one of which is interactions between elements of the quantum working medium. Furthermore, the study of complete Otto cycles inherent in the average cycle also yields interesting insights into the average performance. By analyzing extreme case scenarios, we formulate heuristics to infer the necessary conditions for an engine with uncoupled as well as coupled spin model. It has been shown earlier that the said interaction provides an enhancement of cycle efficiency, with an upper bound that is tighter than the Carnot efficiency. ![]() Quantum thermal machines make use of non-classical thermodynamic resources, one of which include interactions between elements of the quantum working medium. The result in this paper can be generalized to a quantum Brayton cycle with a general coupled system as the working substance. Two pressures can be defined in our isobaric process one corresponds to the external magnetic field (characterized by F_, the subsystem can be a refrigerator, while the total system is a heat engine. The actual Brayton cycle consists of two adiabatic and two isobaric processes. We explore the quantum version of the Brayton cycle with a composite system as the working substance. ![]()
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