Efficiency at maximum power of a heat engine working with a two-level atomic system
Rui Wang, Jianhui Wang, Jizhou He, and Yongli Ma
Accepted
We consider the finite-time operation of a quantum heat engine whose working substance is composed of a two-level atomic system. The engine cycle, consisting of two quantum adiabatic and two quantum isochoric (constant-frequency) processes and working between two heat reservoirs at temperatures Th and Tc ( < Th), is a quantum version of the classical Otto cycle. By optimizing the power output with respect to two frequencies, we obtain the efficiency at maximum power output (EMP) and analyze numerically the effects of the times taken for two adiabatic and two isochoric processes on the EMP. In the absence of internally dissipative friction, we find that the EMP is bounded from the upper side by a function of the Carnot efficiency hC, h+ = hC2/[hC-(1-hC)ln(1-hC)], with hC=1-Tc/Th. This analytic expression is confirmed by our exact numerical result, and identical to the one derived in an engine model based on a mesoscopic or macroscopic system. If the internal friction is included, we find that the EMP decreases as the friction coefficient increases. PACS number(s): 05.70.-a, 03.65.-w