Superposition of Inductive and Capacitive Coupling in Superconducting LC Resonators

TL;DR

This paper experimentally investigates superconducting LC resonators with tunable inductive and capacitive coupling, demonstrating design flexibility and minimal loss variation at millikelvin temperatures.

Contribution

It introduces a versatile resonator design allowing controlled inductive and capacitive coupling with minimal loss variation, advancing superconducting circuit engineering.

Findings

Both inductive and capacitive couplings are achievable with minor design modifications.

The measured loss tangent varies by less than a few percent across designs.

The measurement technique shows high systematic precision.

Abstract

We present an experimental investigation of lumped-element superconducting LC resonators designed to provide different types of coupling to a transmission line. We have designed four resonator geometries including dipole and quadrupole configured inductors connected in parallel with low loss SiNx dielectric parallel-plate capacitors. The design of the resonator allows a small change in the symmetry of the inductor or grounding of the capacitor to allow LC resonators with: 1) inductive coupling, 2) capacitive coupling, 3) both types of coupling, or 4) greatly reduced coupling. We measured all four designs at a temperature of 30mK at different values of power. We compare the extracted data from the four resonator types and find that both capacitive and inductive coupling can be included and that when left off, only a minor change in the circuit design is necessary. We also find a variation in the measured loss tangent of less than a few percent, which is a test of the systematic precision of the measurement technique.