  Superconducting microwave circuits based on coplanar waveguides (CPW) are
susceptible to parasitic slotline modes which can lead to loss and decoherence.
We motivate the use of superconducting airbridges as a reliable method for
preventing the propagation of these modes. We describe the fabrication of these
airbridges on superconducting resonators, which we use to measure the loss due
to placing airbridges over CPW lines. We find that the additional loss at
single photon levels is small, and decreases at higher drive powers.
