In this work, we study coupled quantum systems as working media of thermodynamic machines. With suitable co-ordinate transformation, the coupled system appears to be uncoupled in the new frame of reference. In that case, the global efficiency of the total system is bounded (both from above and below) by the efficiencies of the independent subsystems, provided both the independent subsystems work in the engine mode. This is also true for the coefficient of performance when the coupled system behave as refrigerator. We make a comparative study between coupled spin- $1/2$ systems and coupled quantum oscillators considering analogous interaction for both the systems. Interestingly, for particular kind of interactions, the efficiency of the coupled oscillators outperforms that of the coupled spin- $1/2$ systems when they work as heat engines. However, for same interaction, the coefficient of performance behaves in a reverse manner, while the system work as refrigerator. Therefore coupling can cause opposite effects in the figure of merits of heat engine and refrigerator.In this work, we study coupled quantum systems as working media of thermodynamic machines. With suitable co-ordinate transformation, the coupled system appears to be uncoupled in the new frame of reference. In that case, the global efficiency of the total system is bounded (both from above and below) by the efficiencies of the independent subsystems, provided both the independent subsystems work in the engine mode. This is also true for the coefficient of performance when the coupled system behave as refrigerator. We make a comparative study between coupled spin-$1/2$ systems and coupled quantum oscillators considering analogous interaction for both the systems. Interestingly, for particular kind of interactions, the efficiency of the coupled oscillators outperforms that of the coupled spin-$1/2$ systems when they work as heat engines. However, for same interaction, the coefficient of performance behaves in a reverse manner, while the system work as refrigerator. Therefore coupling can cause opposite effects in the figure of merits of heat engine and refrigerator.

Jul 4, 20160 citations

Coupled Systems

Karl Blum

Springer eBooksJan 1, 19810 citations

Environment-assisted strong coupling regime

Timofey T. Sergeev, I. V. Vovchenko, A. A. Zyablovsky +1 more

Strong coupling regime takes place in open hybrid systems consisting of two or more physical subsystems when the coupling strength between subsystems exceeds the relaxation rate. The relaxation arises due to the interaction of the system with environment. For this reason, it is usually believed that the enhancement of the interaction with environment inevitably leads to a transition of the system from the strong to weak coupling regime. In this paper, we refute this common opinion. We demonstrate the interaction of the coupled system with environment induces an additional coupling between the subsystems that contribute to retention the system in the strong coupling regime. We show that the environmental-induced coupling strength is proportional to the product of the Rabi coupling strength by the gradient of the density of states of the reservoir. There is a critical Rabi coupling strength above which the environmental-induced coupling ensures that the system remains in the strong coupling regime at any relaxation rate. In this case, the strong coupling regime takes place even when the relaxation rate is significantly above the Rabi coupling strength between the subsystems. The critical coupling depends on the gradient of the reservoir density of states. We demonstrate that managing this gradient can serve as an additional tool to control the properties of the coupled systems.Strong coupling regime takes place in open hybrid systems consisting of two or more physical subsystems when the coupling strength between subsystems exceeds the relaxation rate. The relaxation arises due to the interaction of the system with environment. For this reason, it is usually believed that the enhancement of the interaction with environment inevitably leads to a transition of the system from the strong to weak coupling regime. In this paper, we refute this common opinion. We demonstrate the interaction of the coupled system with environment induces an additional coupling between the subsystems that contribute to retention the system in the strong coupling regime. We show that the environmental-induced coupling strength is proportional to the product of the Rabi coupling strength by the gradient of the density of states of the reservoir. There is a critical Rabi coupling strength above which the environmental-induced coupling ensures that the system remains in the strong coupling regime at any relaxation rate. In this case, the strong coupling regime takes place even when the relaxation rate is significantly above the Rabi coupling strength between the subsystems. The critical coupling depends on the gradient of the reservoir density of states. We demonstrate that managing this gradient can serve as an additional tool to control the properties of the coupled systems.

arXiv:2108.07248QuantumApr 13, 202211 citations

Implications of Coupling in Quantum Thermodynamic Machines

GEORGE M. THOMAS, Manik Banik, Sibasish Ghosh A

We study coupled quantum systems as the working media of thermodynamic machines. Under a suitable phase-space transformation, the coupled systems can be expressed as a composition of independent subsystems. We find that for the coupled systems, the figures of merit, that is the efficiency for engine and the coefficient of performance for refrigerator, are bounded (both from above and from below) by the corresponding figures of merit of the independent subsystems. We also show that the optimum work extractable from a coupled system is upper bounded by the optimum work obtained from the uncoupled system, thereby showing that the quantum correlations do not help in optimal work extraction. Further, we study two explicit examples; coupled spin- 1 / 2 systems and coupled quantum oscillators with analogous interactions. Interestingly, for particular kind of interactions, the efficiency of the coupled oscillators outperforms that of the coupled spin- 1 / 2 systems when they work as heat engines. However, for the same interaction, the coefficient of performance behaves in a reverse manner, while the systems work as the refrigerator. Thus, the same coupling can cause opposite effects in the figures of merit of heat engine and refrigerator.We study coupled quantum systems as the working media of thermodynamic machines. Under a suitable phase-space transformation, the coupled systems can be expressed as a composition of independent subsystems. We find that for the coupled systems, the figures of merit, that is the efficiency for engine and the coefficient of performance for refrigerator, are bounded (both from above and from below) by the corresponding figures of merit of the independent subsystems. We also show that the optimum work extractable from a coupled system is upper bounded by the optimum work obtained from the uncoupled system, thereby showing that the quantum correlations do not help in optimal work extraction. Further, we study two explicit examples; coupled spin- 1 / 2 systems and coupled quantum oscillators with analogous interactions. Interestingly, for particular kind of interactions, the efficiency of the coupled oscillators outperforms that of the coupled spin- 1 / 2 systems when they work as heat engines. However, for the same interaction, the coefficient of performance behaves in a reverse manner, while the systems work as the refrigerator. Thus, the same coupling can cause opposite effects in the figures of merit of heat engine and refrigerator.

arXiv:1607.00994EntropySep 8, 201725 citations

Coupled physical systems

David J. Foulis

Foundations of PhysicsJul 1, 198932 citations

1/2

systems and coupled quantum oscillators considering analogous interaction for both the systems. Interestingly, for particular kind of interactions, the efficiency of the coupled oscillators outperforms that of the coupled spin-

1/2

systems when they work as heat engines. However, for same interaction, the coefficient of performance behaves in a reverse manner, while the system work as refrigerator. Therefore coupling can cause opposite effects in the figure of merits of heat engine and refrigerator.