Minimal resonator loss for circuit quantum electrodynamics

Abstract

We report quality factors of up to $500\times {10}^3$ in superconducting resonators at the single photon levels needed for circuit quantum electrodynamics. This result is achieved by using NbTiN and removing the dielectric from regions with high electric fields. As demonstrated by a comparison with Ta, the crucial sources of intensity-dependent loss are dielectrics on the surface of the metal and substrate.