Demonstration of superconducting micromachined cavities

• Published in: Applied physics letters 2015-11, Vol.107 (19)
• Main Authors: Brecht, T., Reagor, M., Chu, Y., Pfaff, W., Wang, C., Frunzio, L., Devoret, M. H., Schoelkopf, R. J.
• Format: Article
• Language: English
• Subjects: APERTURES; Applied physics; Cavity resonators; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; Computation; Conductors; Enclosures; INDIUM; Machining; Micromachining; MICROWAVE RADIATION; Multilayers; Q factors; QUALITY FACTOR; QUANTUM COMPUTERS; Quantum computing; QUANTUM ELECTRODYNAMICS; Quantum phenomena; Quantum theory; QUBITS; Qubits (quantum computing); Seams; SUPERCONDUCTING CAVITY RESONATORS; Superconductivity; Transmission lines
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.4935541

Superconducting enclosures will be key components of scalable quantum computing devices based on circuit quantum electrodynamics. 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.