Low-loss microwave components are used in many superconducting resonant circuits from multiplexed readouts of low-temperature detector arrays to quantum bits. Two-level system defects in amorphous dielectric materials cause excess energy loss. In an effort to improve capacitor components, we have used optical lithography and micromachining techniques to develop superconducting parallel-plate capacitors in which lossy dielectrics are replaced by vacuum gaps. Resonance measurements at 50 mK on lumped LC circuits that incorporate these vacuum-gap capacitors (VGCs) reveal loss tangents at low powers as low as 4x10^{-5}, significantly lower than with capacitors using amorphous dielectrics. VGCs are structurally robust, small, and easily scaled to capacitance values above 100 pF.
@article{arxiv.0810.1976,
title = {Vacuum-Gap Capacitors for Low-Loss Superconducting Resonant Circuits},
author = {Katarina Cicak and Michael S. Allman and Joshua A. Strong and Kevin D. Osborn and Raymond W. Simmonds},
journal= {arXiv preprint arXiv:0810.1976},
year = {2015}
}