Performance of the collective three-level quantum thermal engine

We investigate the performance of a microscopic quantum heat engine consisting of V- or -type emitters interacting collectively or independently when being in contact with environmental thermal reservoirs. Though the efficiency of a Carnot's cycle is always higher than those associated with these setups, we have found that the performance of the cooperative -type heat engine may be larger than that of the V type under similar conditions. Cooperativity among the emitters plays an important role for the -type setup, significantly improving its performance, while it is less relevant for a V-type thermal engine. This is because the population inversion on the working atomic transition as well as its off-diagonal elements behave differently for these two atomic ensembles.