  Recent theoretical and experimental studies in quantum heat engines show
that, in the quasi-static regime, it is possible to have higher efficiency than
the limit imposed by Carnot, provided that engineered reservoirs are used. The
quasi-static regime, however, is a strong limitation to the operation of heat
engines, since infinitely long time is required to complete a cycle. In this
paper we propose a two-level model as the working substance to perform a
quantum Otto heat engine surrounded by a cold thermal reservoir and a squeezed
hot thermal reservoir. Taking advantage of this model we show a striking
achievement, that is to attain unity efficiency even at non null power.
