Four-level Quantum Heating Cycle And Refrigeration Cycle

With the rapid development of nanotechnology and quantum information, The field ofquantum thermodynamics, physicists also gradually attracted more and more attention. Westudied the entanglement of quantum heat engine main purpose is to improve the efficiency ofquantum heat engine, which go beyond the limit of classical heat engine efficiency, under thecondition of meet the positive work, to the maximum extent engine output power.In this paper, our research work about quantum thermodynamics discusses theentanglement of quantum heat cycle under different working substance and the cold cycle1.We construct an entangled quantum heat engines based on two coupled qubits XXZmodel with DM interaction. The relations between the entanglement and heat transfer, workoutput and efficiency are analyzed for different anisotropic parameters. The results show thatthe second law of thermodynamics holds in entangled systems and the isolines for theefficiency are looped curves. When the anisotropic parameter Δ is small enough, the heatengine can operate in bothC₁> C₂andC₁<C₂, however, when Δ is large, the heat engineoperates inC₁> C₂only.2. To contain the DM interaction of anisotropic Heisenberg model two bits of workmaterial build a four-level entangled quantum refrigeration cycle, from the Angle of therealization of quantum entanglement in the refrigeration cycle system heat exchange with theoutside world, input power and refrigeration coefficient of thermodynamic properties3. We establish a quantum Otto engine cycle, in which the working substance contactswith squeezed reservoirs during the two quantum isochoric processes. Due to the effects ofsqueezing, the working substance can be heated to a higher effective temperature, which leadsto many interesting features different from the ordinary ones such as （1） for the qubit asworking substance, if we choose the squeezed parameters properly, the positive work can beexported even whenT_H <T_L, whereTH andTL are the temperatures of the hot and coolreservoirs, respectively;（2） The effciency can be higher than classical Carnot effciency.These results do not violate the second law of thermodynamics.