A semiempirical model for two-level system noise in superconducting microresonators

Abstract

We present measurements of the low-temperature excess frequency noise of four niobium superconducting coplanar waveguide microresonators, with center strip widths sr ranging from 3 to 20 µm. For a fixed internal power, we find that the frequency noise decreases rapidly with increasing center strip width, scaling as 1/s_r^1.6. We show that this geometrical scaling is readily explained by a simple semiempirical model which assumes a surface distribution of independent two-level system fluctuators. These results allow the resonator geometry to be optimized for minimum noise.

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