  We investigate energy transfer by the radiation from a cavity quantum
electrodynamics (QED) system in the context of quantum thermodynamics. We
propose a method of decomposing it into work and heat within the framework of
quantum master equations. We find that the work and heat correspond
respectively to the coherent and incoherent parts of the radiation. In the
derivation of the method, it is crucial to investigate the dynamics of the
system that receives the radiation from the cavity.
