不可逆自旋量子制冷循环参数的优化设计

基于量子主方程和半群逼近方法，研究以许多无相互作用的自旋-1/2系统为工质的、由两个绝热和两个等磁场过程组成的不可逆量子制冷循环的一般性能特性。导出循环的性能系数、制冷率和输入功率等重要性能参数的表达式。应用数值求解，对受有限循环时间约束的制冷率进行了优化，计算了最大制冷率和相应的最佳性能参数，确定了性能系数的最佳区域和工质温度及两个等磁场过程时间的优化范围。进而详细分析了高温下循环的优化性能，所得结果被进一步推广，以致可直接用来描述由自旋-J系统为工质的量子制冷循环的性能。

Parametric optimum design of an irreversible spin quantum refrigeration cycle

The general performance characteristics of an irreversible quantum refrigeration cycle using many non-interacting spin-1/2 systems as the working substance and consisting of two adiabatic and two isomagnetic field processes are investigated, based on the quantum master equation and semi-group approach. Expressions for several important performance parameters such as the coefficient of performance, cooling rate and power input are derived. By using numerical solutions, the cooling rate of the refrigeration cycle subject to the finite cycle duration is optimized. The maximum cooling rate and the corresponding parameters are calculated numerically. The optimal region of the coefficient of performance and the optimal ranges of the temperatures of the working substance and the times spent on the two isomagnetic field processes are determined. Moreover, the optimal performance of the cycle in the high-temperature limit is also analysed in detail. The results obtained here are further generalized, so that they may be directly used to describe the performance of the quantum refrigeration cycle using spin-J systems as the working substance.