Compact superconducting microwave resonators based on Al-AlOx-Al capacitor

Abstract

We address the scaling-up problem for superconducting quantum circuits by using lumped-element resonators based on an alternative fabrication method of aluminum -- aluminum oxide -- aluminum ($Al/Al{\mathrm{O}}_{\mathrm{x}}/Al$) parallel-plate capacitors. The size of the resonators is only 0.04~$\mathrm{m}{\mathrm{m}}^2$, which is more than one order smaller than the typical size of coplanar resonators (1~$\mathrm{m}{\mathrm{m}}^2$). The fabrication method we developed easily fits into the standard superconducting qubits fabrication process. We have obtained capacitance per area 14~fF/$\mu {\mathrm{m}}^2$ and the internal quality factor $1\times 10^3-8\times 10^3$ at the single-photon level. Our results show that such devices based on $Al/Al{\mathrm{O}}_{\mathrm{x}}/Al$ capacitors could be further applied to the qubit readout scheme, including resonators, filters, amplifiers, as well as microwave metamaterials and innovative types of qubits, such as $0-\pi$ qubit.