Superconducting 3D platform for characterization of dielectric materials for quantum computing applications*

Superconducting quantum computing devices demonstrate high potential for scalability, ease of control and, ultimately, provide a pathway for building large scale practical quantum computing (QC) architectures. One of the main factors limiting performance of 2D superconducting QC devices are decoherence and loss due to unwanted interaction with uncontrolled degrees of freedom. It has been shown that amorphous oxides forming on unprotected surfaces of superconducting devices produce the main contribution to the total loss. However, contribution of the substrate QC devices are fabricated on becomes more apparent as surface oxide issue is successfully tackled by selection of better superconducting materials and novel fabrication procedures. Effect of substrate is even more significant in the case of 3D architectures where QC devices fabricated on dielectric substrates are placed inside 3D superconducting cavity resonators. In 3D QC architectures microwave fields penetrate inside the bulk of a substrate that is supporting the qubits which causes significant degradation of coherence time of the system "QC device + resonator".

We demonstrate and discuss the experimental testbed that allows characterization of various dielectric materials in sub-1K temperatures and wide frequency range from 5 - 7 GHz. Our measurements of the loss tangent as a function of frequency, temperature, and probing power help to identify the dominant loss mechanisms and select optimal materials and fabrication procedures for the next generation of QC devices.