| Quantum thermodynamics is a branch of new developing subject produced by the intersection of quantum mechanics and classical thermodynamics.In this emerging field,quantum heat engine is one of the main research contents in quantum thermodynamics.It is well known that the main working substance of a qauntum heat engine is quantum system,and the interaction of the quantum system can produce rich non-classical effects,such as quantum coherence,quantum discord and so on.Many investigations have shown that the non-classical effects of working substance play an important role in improving the characteristics of quantum heat engines.In this paper,using the basic theories of quantum thermodynamics and quantum optics,the thermodynamic properties of the quantum Otto heat engine with a spin system as the working substance have been studied.The study results have important academic significance and reference value.The main contents and innovative results are as follows:In Chapter 1,the historical development of quantum thermodynamics is introduced briefly.Then,introducing the current research of quantum heat engine at home and abroad.Finally,the main works of this paper are summarized.In Chapter 2,the first law of classical thermodynamics in the form of quantum mechanics is reviewed firstly and the basic concepts of quantum thermodynamics related are introduced,such as quantum isothermal process,quantum isochoric process,quantum adiabatic process and the effective temperature.Next,the validity and universality of the second law of thermodynamics are elaborated.Finally,expounding the basic theory of quantum Otto cycle,comparing with the theory of classical Otto cycle and proving the equivalence between the quantum Otto heat engine and the classic Otto heat engine.In Chapter 3,a brief review of the basic theory of quantum spin systems and an introduction of the basic concepts and measurement methods of two non-classical effects about quantum coherence and quantum discord are givenIn Chapter 4,the influence of the non-classical effect of working substance on the characteristics of the quantum Otto heat engine is investigated.Firstly,the influence of quantum coherence of working substance,twoqubit or three-qubit Heisenberg XXX models,on quantum Otto heat engines is studied.The results show that:?1?In the absence of external magnetic field,two quantum Otto engines can produce the positive work and the efficiency in the quantum coherence region Cl1<Cl2(where Cl1 and Cl2 indicate the coherence of the system when the final states of the first and second isochoric processes reach the thermal equilibrium. respectively).When the coherence Cl1 is fixed,the efficiency decreases with the coherence Cl2 and when the coherence Cl2 is fixed,the efficiency increases monotonically with the coherence Cl1;?2?In the presence of an external magnetic field, the coherence regions of the two quantum Otto heat engines that produce the positive work and the effciency are expanded to Cl1<Cl2 and Cl1>Cl2;?3?Regardless of the presence of an external magnetic field,the efficiency of the two kinds of the quantum Otto heat engines can not reach Carnot efficiency;?4?The quantum heat engine with the working substance of the three-qubit Heisenberg XXX model extracts more positive work than the quantum heat engine with working substance of the twoqubit Heisenberg XXX model.Then,when the final state reaches the thermal equilibrium,the influence of the difference of quantum discord of working substance between the second isochoric process and the first isochoric process is studied.The results show that the difference of quantum discord helps the quantum heat engine to extract more positive work.When the difference of quantum discord is zero,the quantum heat engine can not operate normally. indicating that the difference of quantum discord of the working substance is an important resource for the operation of the quantum heat engineIn Chapter 5,under an inhomogeneous external magnetic field,with DzyaloshinskiiMoriya?DM?interaction of spin?1/2,1?Heisenberg XXX model as working substance,the properties of a quantum Otto heat engine are studied.The effects of DM interaction on thermodynamic quantities are discussed.The results show that:In the decreasing area of the positive work and efficiency formed by weak coupling strength,DM interaction inhibits the extraction of the positive work and the improvement of effciency:In the recovery area of the positive work and efficiency formed by large coupling strength,DM interaction is conducive to the extraction of positive work and the improvement of efficiency;In the stable area of positive work and efficiency formed by larger coupling strength,DM interaction is not conducive to extract more positive work,but it is beneficial to improve efficiency.With the increase of the DM interaction,the value of local work of the particle of the spin-1/2 is always less than zero,indicating that the particle of the spini is a refrigerator.While the value of local work of the particle of the spin-1 is always more than zero,indicating that the particle of the spin-1 is a heat engine.In Chapter 6,a summary and outlook are presented. |
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