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## Main Question or Discussion Point

A textbook gives the following interaction Hamiltonian describing the interaction of an atom (having transition dipole moment [itex]\mu[/itex]) with a photon whose polarization can be [itex]\epsilon_{1}[/itex] or [itex]\epsilon_{2}[/itex]):

H = g [itex]\Sigma[/itex][itex]^{2}_{s=1}[/itex][itex]\mu[/itex][itex]\bullet[/itex][itex]\epsilon[/itex]

where [itex]\sigma^{-}[/itex] is Pauli spin-flip operator and a[itex]^{+}_{s}[/itex] is the creation/annihilation operator.

What does "h.c." stand for in this formula?

H = g [itex]\Sigma[/itex][itex]^{2}_{s=1}[/itex][itex]\mu[/itex][itex]\bullet[/itex][itex]\epsilon[/itex]

_{s}[itex]\sigma^{-}[/itex]a[itex]^{+}_{s}[/itex] + h.c.where [itex]\sigma^{-}[/itex] is Pauli spin-flip operator and a[itex]^{+}_{s}[/itex] is the creation/annihilation operator.

What does "h.c." stand for in this formula?