Performance of the collective three-level quantum thermal engine

We investigate the performance of a microscopic quantum heat engine\nconsisting of V- or Lambda-type emitters interacting collectively or\nindependently when being in contact with environmental thermal reservoirs.\nThough the efficiency of a Carnot's cycle is always higher than those\nassociated with these setups, we have found that the performance of the\ncooperative Lambda-type heat engine may be larger than that of the V-type under\nsimilar conditions. Cooperativity among the emitters plays an important role\nfor the Lambda-type setup, significantly improving its performance, while is\nless relevant for a V-type thermal engine. This is because the population\ninversion on the working atomic transition as well as its off-diagonal elements\nbehave differently for these two atomic ensembles.\n