Demonstration of superconducting micromachined cavities

TL;DR

This paper demonstrates superconducting micromachined cavities with high quality factors using indium, enabling scalable multilayer quantum circuits for quantum computing.

Contribution

It introduces a novel micromachining technique with indium to create low-loss superconducting cavities with high quality factors.

Findings

Superconducting indium can form low-loss RF seams.

Achieved a quality factor of two million in micromachined resonators.

Demonstrated multilayer integration for scalable quantum circuits.

Abstract

Superconducting enclosures will be key components of scalable quantum computing devices based on circuit quantum electrodynamics (cQED). Within a densely integrated device, they can protect qubits from noise and serve as quantum memory units. Whether constructed by machining bulk pieces of metal or microfabricating wafers, 3D enclosures are typically assembled from two or more parts. The resulting seams potentially dissipate crossing currents and limit performance. In this Letter, we present measured quality factors of superconducting cavity resonators of several materials, dimensions and seam locations. We observe that superconducting indium can be a low-loss RF conductor and form low-loss seams. Leveraging this, we create a superconducting micromachined resonator with indium that has a quality factor of two million despite a greatly reduced mode volume. Inter-layer coupling to this type of resonator is achieved by an aperture located under a planar transmission line. The described techniques demonstrate a proof-of-principle for multilayer microwave integrated quantum circuits for scalable quantum computing.