| In recent years, with the rapid development of the experimental technology and quantum information science, a number of thermodynamic phenomena have been concerned from microscopic perspective. Quantum thermodynamic has become a focus of the modern thermodynamic. Quantum thermodynamics is the study of thermodynamical processes within the framework of quantum dynamics. And it is devoted to unraveling the intimate connection between the laws of thermodynamics and their quantum origin. There are many different types of quantum heat engine, such as quantum Carnot engine, quantum Otto engine, and quantum Brayton engine. They are closely related to the experimental studies of energy conversion in micro and nano scales by using laser transmission, quantum dot contact and so on, which give effective way to promote the establishment and improvement of quantum thermodynamics.Quantum heat engine produce work by using quantum particles and quantum systems as the working substance. Because of the nature of the quantum matter, there are a lot of inherent differences between quantum heat engines and their classical counterparts. Inspired by the properties of classical thermodynamic processes and cycles, the quantum analogues of the processes and cylces have been developed and discussed in more and more different quantum systems. Based on the differences, we focus our research on quantum isoenergetic process and the effects on different quantum thermodynamic cycles. The main contents will be presented as follow.(1) The fundamental conceptions and classical thermodynamic laws are introduced and the development, current situation and significance of quantum thermodynamic cycles are analyzed briefly.(2) The main content is about the quantum isoenergetic process. A two-level quantum system is adopted to illustrate the difference between quantum isoenergetic process and quantum isothermal process. Based on the characteristics of quantum thermodynamic processes, it is possible for a two-level quantum engine working between a heat bath and an energy bath. The efficiency of such kind of engine cycle is derived to establish a relationship with quantum Carnot efficiency. Furthermore, by considering the finite time of a full cycle, the power output of this kind of quantum engine can be obtained. It is found that the efficiency and power output are both closely depend on the quantum isothermal process, in which the probability distributions at the initial and final states are essential. Therefore, the performance of the engine cycle can be optimized by preparing the quantum states of the isothermal process. There exist lower bounds of efficiency to guarantee the engine working at the optimal regions.(3) A quantum particle trapped in harmonic oscillator potential is adopted as working substance to construct a quantum engine cycle including both quantum isothermal process and quantum isoenergetic process. It is explicitly expounded that the thermodynamic behavior of these two quantum processes are different from each other. Moreover, this specific type of engine cycle exhibits peculiar properties in its efficiency. There exists an optimized expansion ratio of the width of the harmonic potential well, and yields the maximum engine efficiency. This abnormal phenomenon becomes prominent when the temperature of the heat bath is decreasing, which indicates that the quantum properties of the system play more and more important role.(4) We introduce the basic concepts of quantum entanglement and set up a new cyclic model of quantum Carnot heat engine, which consists of two quantum isoenergetic processes and two quantum adiabatic processes. The performance of this Carnot engine, whose working substance consists of quantum entanglement particles confined to an infinite square well potential, is obtained. It is shown that the mass of the quantum entanglement particles have an important effect on the efficiency of this engine.(5) In this chapter, we summarize the whole paper and give a prospect for the future work. |
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