Superconducting Caps for Quantum Integrated Circuits

We report on the fabrication and metrology of superconducting caps for qubit circuits. As part of a 3D quantum integrated circuit architecture, a cap chip forms the upper half of an enclosure that provides isolation, increases vacuum participation ratio, and improves performance of individual resonant elements. Here, we demonstrate that such caps can be reliably fabricated, placed on a circuit chip, and form superconducting connections to the circuit.