Cavity induced transparency

We consider a two-level atom inside a cavity. We find that the absorption spectrum of the atom may exhibit a hole at line center for a weak probe. This hole appears when the cavity linewidth is small compared to the atom-field coupling strength, which is itself smaller than the atom's free space linewidth. In the weak-field limit, this system is analogous to a three-level atom, where similar absorption holes at line center occur due to electromagnetically induced transparency (EIT). In EIT, a strong field is required to strongly mix the upper two levels, whereas in the system we consider, it is the atom-field coupling strength that plays this role. An alternate explanation in terms of interference between the cavity field and atomic polarization is given. We also examine the driven cavity case.