  Classically, the power generated by an ideal thermal machine cannot be larger
than the Carnot limit. This profound result is rooted in the second law of
thermodynamics. A hot question is whether this bound is still valid for
microengines operating far from equilibrium. Here, we demonstrate that a
quantum chiral conductor driven by AC voltage can indeed work with efficiencies
much larger than the Carnot bound. The system also extracts work from common
temperature baths, violating Kelvin-Planck statement. Nonetheless, with the
proper definition, entropy production is always positive and the second law is
preserved. The crucial ingredients to obtain efficiencies beyond the Carnot
limit are: i) irreversible entropy production by the photoassisted excitation
processes due to the AC field and ii) absence of power injection thanks to
chirality. Our results are relevant in view of recent developments that use
small conductors to test the fundamental limits of thermodynamic engines.
