" Scully's design employs lasers, mirrors and a concept known as "quantum coherence" to drive a piston with less wasted energy than in the Carnot model".

The quantum thermodynamics of systems slightly _out_of_equilibrium_ is an area of current interest. In the particular form of _nonequilibrium_ considered here, quantum coherence... The total system _entropy_ is constantly _increasing_, and the physics behind the _second_law_ is _not_violated_. However, quantum coherence does allow certain features of engine operation beyond the classical limit.