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1. Spontaneous Emission

   Linked via "excited atomic state"

   The modern understanding, rooted in Quantum Electrodynamics (QED)/), attributes the process to the interaction between the material dipole moment and the virtual photons present in the vacuum state. In the semi-classical framework, the electric field $\mathbf{E}(\mathbf{r}, t)$ is treated classically, which successfully models absorption and stimulated emission (as noted in introductory texts, often involving the [electric dipole approximation](/entries/electric-dipole-…