Geometric scaling of two-level-system loss in superconducting resonators

Abstract

We perform an experimental and numerical study of dielectric loss in superconducting microwave resonators at low temperature. Dielectric loss, due to two-level systems, is a limiting factor in several applications, e.g. superconducting qubits, Josephson parametric amplifiers, microwave kineticinductance detectors, and superconducting single-photon detectors. Our devices are made of disordered NbN, which, due to magnetic-field penetration, necessitates 3D finite-element simulation of the Maxwell-London equations at microwave frequencies to accurately model the current density and electric field distribution. From the field distribution, we compute the geometric filling factors of the lossy regions in our resonator structures and fit the experimental data to determine the intrinsic loss tangents of its interfaces and dielectrics. We emphasise that the loss caused by a spin-on-glass resist such as hydrogen silsesquioxane (HSQ), used for ultrahigh lithographic resolution relevant to the fabrication of nanowires, and find that, when used, HSQ is the dominant source of loss, with a loss tangent of δ i HSQ = 8 × 10 −3 .

Bidirectional interconversion of microwave and light with thin-film lithium niobate

“…2 c). This air-clad architecture not only enables long-time stable operation of TFLN transduction devices at cryogenic temperatures; it will also benefit future integration of superconducting qubits because the amorphous oxide buffer is known to host the two-level-systems that impact the qubit coherence 45 , 46 .…”

“…The improved efficiency and stability lead to the demonstration of the bidirectional conversion process with TFLN. This buffer-free architecture is also advantageous for future integration with superconducting circuits, where amorphous oxides are undesired for their role in hosting two-level systems 45 , 46 . The impact of device packaging on the residual RF loss is further examined.…”

Bidirectional interconversion of microwave and light with thin-film lithium niobate

“…2(c)). This new air-clad architecture not only enables long-time stable operation of TFLN transduction devices at cryogenic temperatures; it will also benefit future integration of superconducting qubits because the amorphous oxide buffer is known to host the two-level-systems that impact the qubit coherence [45,46].…”

“…The improved efficiency and stability lead to the first demonstration of bidirectional conversion process with TFLN. This buffer-free architecture is also advantageous for future integration with superconducting cir- cuits, where amorphous oxides are undesired for their role in hosting two-level systems [45,46]. The impact of device packaging on the residual RF loss is further examined.…”

Qubit-compatible substrates with superconducting through-silicon vias

“…Overetching past the metal layer is small, less than roughly 50 nm, and no additional trenching is applied. The exact dimensions of the CPW cross section are significant when making direct quantitative comparisons since in low-loss resonators, the losses are generally dominated by material imperfections in thin interface layers between different materials, and the participation factors of different interfaces are somewhat geometry dependent [32]- [35]. In terms of density and role of TSVs, we use four types of layouts on the measured devices: (a) no TSVs and no ground plane on the back used as reference, (b) sparse TSVs stitching the ground planes on the front and back, (c) dense TSVs stiching the ground planes, and (d) sparse TSVs stiching the grounds and TSVs terminating the resonators to the ground on the back.…”