Abstract: A new model of a quantum heat engine cycle is established in which the working substance consists of many non-interacting spin-1/2 systems.Performance characteristics of the cycle and time evolution of the spin angular momentum are investigated, based on the quantum master equation and a semi-group approach.The general expressions of efficiency and power output are derived.Further, at high temperatures the optimal relations of efficiency and power output are studied in detail.Optimal performance of heat engine cycles is analyzed from a microscopic model.

Key words: spin systems, quantum heat engine cycle, performance analysis