  We consider models in which the (transverse) photon mass is non-zero during
inflation and drops to zero non-adiabatically at the end of inflation. Through
this process, vacuum fluctuations of the photon field are converted into
physical, long-wavelength modes with high amplitude. The resulting spectrum of
the field strength is approximately B_l ~ 1/l, where l is the relevant
coherence scale. With a reasonable model of field evolution we obtain, on
comoving galactic scales, a magnetic field strong enough to seed a dynamo
mechanism and generate the observed galactic magnetic fields.
