We consider the ground state of an atom in the framework of non-relativistic
qed. We show that the ground state as well as the ground state energy are
analytic functions of the coupling constant which couples to the vector
potential, under the assumption that the atomic Hamiltonian has a
non-degenerate ground state. Moreover, we show that the corresponding expansion
coefficients are precisely the coefficients of the associated
Raleigh-Schroedinger series. As a corollary we obtain that in a scaling limit
where the ultraviolet cutoff is of the order of the Rydberg energy the ground
state and the ground state energy have convergent power series expansions in
the fine structure constant α, with α dependent coefficients
which are finite for α≥0.Comment: 37 page