# Interaction hamiltonian?

1. Nov 14, 2011

### phonon44145

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

H = g $\Sigma$$^{2}_{s=1}$$\mu$$\bullet$$\epsilon$s$\sigma^{-}$a$^{+}_{s}$ + h.c.

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

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

2. Nov 14, 2011

### Polyrhythmic

Hermitean conjugate.

3. Nov 14, 2011

### phonon44145

Thanks for the quick reply. But I still cannot quite see how to write the second term explicitly. Am I correct in assuming that μ and ϵ1, ϵ2 should not change, σ− will become σ+, and creation operator will change to annihilation operator?

4. Nov 15, 2011

### phonon44145

Also, what does g stand for - gyromagnetic ratio?