Nonresonant two-level transitions: Insights from quantum thermodynamics

Based on concepts from quantum thermodynamics, the two-level system coupled to a single electromagneticmode is analyzed. Focusing on the case of detuning, where the mode frequency does not match the transitionfrequency, effective energies are derived for the levels and the photon energy. It is shown that these should be usedfor energy exchange with fermionic and bosonic reservoirs in the steady state to achieve a thermodynamicallyconsistent description. While recovering known features such as frequency pulling or Bloch gain, this sheds lighton their thermodynamic background and allows for a coherent understanding