Low-loss parallel-plate capacitor for superconducting quantum circuits

Many coherent superconducting devices utilize coplanar waveguide resonators and co-planar (lateral) capacitors to avoid significant electric field participation in lossy dielectric surfaces and interfaces. The trade-off is a much larger footprint per device. In this work, we present a relatively low-loss parallel-plate capacitor that has a specific capacitance (~12 fF/µm²) that is orders of magnitude higher than for coplanar capacitors. The capacitor features <2% cross-chip variability and a loss tangent of approximately 2E-5. We have demonstrated T₁ times of 6-20 µs in flux qubits shunted with this parallel-plate capacitor for varying degrees of designed electric-field participation.

 

This material is based upon work supported by the Department of Defense under Air Force Contract No. FA8702-15-D-0001. Any opinions, findings, conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Department of Defense.