Experimental demonstrations of high-Q superconducting coplanar waveguide resonators

We successfully designed and fabricated an absorption-type of superconducting coplanar waveguide （CPW） resonators. The resonators are made from a niobium film （about 160 nm thick） on a high-resistance Si substrate, and each resonator is fabricated as a meandered quarter-wavelength transmission line （one end is short to the ground and another end is capacitively coupled to a through feedline）. With a vector network analyzer we measured the transmissions of the applied microwave through the resonators at ultra-low temperature. The obtained loaded quality factors are significantly high, i.e. up to -106. When the temperature increases slowly from the base temperature （20 mK）, the resonance frequencies of the resonators are blue shifted and the quality factors are lowered slightly. In principle, this type of device can integrate a series of CPW resonators with a common feedline, making it a promising candidate as the data bus for coupling distant solid-state qubits and the sensitive detector of single photons.