Laser fluctuation effects in an EIT engine

In contact with a hot and a cold reservoir, the three-level atom driven by a strong coupling field generates photons via a sequence of transitions that mimics the running process of a heat engine. The brightness of the output photon can be much larger than that of the hot reservoir, and its efficiency could be larger than that of the Carnot engine [ Phys. Rev. A 94 , 053859 ( 2016 ) PLRAAN 1050-2947 10.1103/PhysRevA.94.053859 ]. The core element of the mechanism is an interference effect called electromagnetically induced transparency caused by the coupling field, which is commonly a perfect laser without any random change in the phase. In this paper, we investigate a more realistic model where the temporal fluctuation of the coupling field is considered. By applying the laws of thermodynamics in the analysis, we find that in addition to the reduced power of the engine, a relatively strong fluctuation changes the properties of the system radically, even making it lose the quality of being a heat engine. We have found the corresponding criteria for the maximal allowed fluctuation. The entropy changes when the engine works below the laser threshold suggest that the effect of the fluctuation is equivalent to increasing the temperature of the cold reservoir.