Quantum heat engine with multilevel quantum systems.

By reformulating the first law of thermodynamics in the fashion of quantum-mechanical operators on the parameter manifold, we propose a universal class of quantum heat engines (QHE) using the multilevel quantum system as the working substance. We obtain a general expression of work for the thermodynamic cycle with two thermodynamic adiabatic processes, which are implied in quantum adiabatic processes. We also classify the conditions for a 3-level QHE to extract positive work, which is proved to be looser than that for a 2-level system under certain conditions. As a realistic illustration, a 3-level atom system with dark state configuration manipulated by a classical radiation field is used to demonstrate our central idea.