For systems with non-zero net charge, the dipole moment depends on the choice of origin (see Does the dipole moment depend on the choice of origin?). How then, can the probability of emission/absorption of light by an atom depend on the angle between the dipole moment and the electric-field component of the light wave?
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$\begingroup$ the net charge of an atom is zero, no? And in any case classical modeling is no good for atoms, it has to be a photon interacting which has no electric field components, just energy and spin. $\endgroup$– anna vCommented Oct 11, 2021 at 5:50
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$\begingroup$ Atoms are neutral. Could you clarify your question? @annav stimulated absorption can be evaluated within a semiclassical approximation where photons do not appear. $\endgroup$– GiorgioP-DoomsdayClockIsAt-90Commented Oct 11, 2021 at 5:55
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$\begingroup$ Consider a charged atom or system of atoms. Single photon emitters, for example point defects in crystals, emit/absorb photons with highest probability when the incoming/outgoing photon direction is perpendicular to the transition dipole moment. Just doesn't make sense if the dipole moment is ill-defined. $\endgroup$– KenCommented Oct 11, 2021 at 5:58
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1$\begingroup$ Does this answer your question? Does the dipole moment depend on the choice of origin? $\endgroup$– Roger V.Commented Oct 11, 2021 at 8:09
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$\begingroup$ As Ken says, we could be calculating the interaction with an ion so the proposed duplicate is not actually a duplicate. $\endgroup$– John RennieCommented Oct 11, 2021 at 8:38
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