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Published April 14, 2008 | public
Journal Article Open

Experimental evidence for a surface distribution of two-level systems in superconducting lithographed microwave resonators

Abstract

We present measurements of the temperature-dependent frequency shift of five niobium superconducting coplanar waveguide microresonators with center strip widths ranging from 3 to 50 µm, taken at temperatures in the range of 100–800 mK, far below the 9.2 K transition temperature of niobium. These data agree well with the two-level system (TLS) theory. Fits to this theory provide information on the number of TLSs that interact with each resonator geometry. The geometrical scaling indicates a surface distribution of TLSs and the data are consistent with a TLS surface layer thickness of the order of a few nanometers, as might be expected for a native oxide layer.

Additional Information

©2008 American Institute of Physics. Received 29 February 2008; accepted 17 March 2008; published 17 April 2008. We thank John Martinis, Clare Yu, and Sunil Golwala for useful discussions. The device was fabricated in the University of California, Berkeley, Microfabrication Laboratory. This work was supported, in part, by the NASA Science Mission Directorate, JPL, the Gordon and Betty Moore Foundation, and Alex Lidow, a Caltech Trustee.

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August 22, 2023
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